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9-10th Class

Force In Very Easy Words

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Force: Class 9 Physics Chapter Notes, Summary, MCQs & Exam Guide

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Complete Class 9 Physics Force chapter notes, summary, MCQs, and exam tips for easy learning and scoring high in exams.

Introduction to the Chapter Force

The chapter Force is a fundamental topic in Class 9 Physics that deals with the interaction between objects that can change their motion or shape. Forces are everywhere—pushing a door, pulling a rope, or even gravity pulling an apple. Understanding forces helps students grasp motion, mechanics, and real-life applications.

This chapter introduces the concept of force, its types, units, and laws governing it, such as Newton’s laws of motion. Students will learn how to calculate force, understand its effects, and apply these concepts in solving practical problems and competitive exams.

Short Notes (Bullet Points)

  • Definition of Force: A force is a push or pull upon an object resulting from its interaction with another object.
  • Unit of Force: Newton (N) in SI units.
  • Types of Forces:
    • Contact Forces: Applied force, frictional force, tension, normal force
    • Non-contact Forces: Gravitational force, magnetic force, electrostatic force
  • Effects of Force:
    • Change in speed (acceleration/deceleration)
    • Change in direction of motion
    • Change in shape of objects
  • Balanced and Unbalanced Forces:
    • Balanced forces: No change in motion
    • Unbalanced forces: Cause acceleration
  • Newton’s Laws of Motion:
    • First Law: Law of inertia
    • Second Law: F = ma
    • Third Law: Action-Reaction
  • Friction: Force opposing motion between surfaces
  • Gravity: A force of attraction between masses
  • Pressure: Force per unit area

Detailed Summary of Force (1000–1200 words)

The chapter Force in Class 9 Physics is essential for understanding the interactions that govern motion and stability of objects. Force is a physical quantity that can cause an object to accelerate, decelerate, remain in equilibrium, or change its shape.

Nature and Definition of Force

A force can be defined as a push or pull exerted on an object. Forces are vector quantities, meaning they have both magnitude and direction. The SI unit of force is the Newton (N), defined as the force required to accelerate a 1 kg mass by 1 m/s².

Types of Forces

Forces are categorized as:

  1. Contact Forces: These require physical contact between objects. Examples include:
    • Frictional force: Opposes motion
    • Applied force: Direct push or pull
    • Tension: Force along a stretched rope
    • Normal force: Perpendicular contact force
  2. Non-Contact Forces: These act without physical contact:
    • Gravitational force: Attraction between masses
    • Magnetic force: Attraction or repulsion between magnets
    • Electrostatic force: Force between charged objects

Effects of Force

A force can:

  • Change the speed of an object
  • Alter its direction
  • Modify its shape
  • Keep it stationary under equilibrium

Balanced and Unbalanced Forces

  • Balanced forces: Two forces acting on an object in opposite directions with equal magnitude result in no motion.
  • Unbalanced forces: Unequal forces cause acceleration according to Newton’s Second Law.

Newton’s Laws of Motion

  1. First Law (Law of Inertia):
    An object remains at rest or in uniform motion unless acted upon by an external force.
  2. Second Law:
    The acceleration of an object is directly proportional to the net force and inversely proportional to its mass:

   F = ma

For every action, there is an equal and opposite reaction.

Friction

Friction opposes motion and depends on the nature of surfaces. Types include:

  • Static friction: Prevents starting motion
  • Kinetic friction: Acts on moving objects
    Friction is necessary for walking, driving, and stopping vehicles but also causes energy loss.

Gravity

Gravity is a universal force that pulls objects toward the center of the Earth. Weight is the gravitational force experienced by an object:


W = mg

Pressure

Pressure is defined as force per unit area:


P = \frac{F}{A}

Real-Life Applications

  • Designing brakes in vehicles
  • Calculating weights and forces in structures
  • Understanding motion in sports and machinery

By understanding these concepts, students can solve problems efficiently, learn experiment-based applications, and build a foundation for higher studies in mechanics.

Flowchart / Mind Map (Text-based)

Force
│
├─ Definition & Unit
│   └─ Newton (N)
│
├─ Types
│   ├─ Contact Forces
│   │   ├─ Friction
│   │   ├─ Applied Force
│   │   ├─ Tension
│   │   └─ Normal Force
│   └─ Non-Contact Forces
│       ├─ Gravitational
│       ├─ Magnetic
│       └─ Electrostatic
│
├─ Effects
│   ├─ Change in Speed
│   ├─ Change in Direction
│   └─ Change in Shape
│
├─ Newton's Laws
│   ├─ First Law (Inertia)
│   ├─ Second Law (F=ma)
│   └─ Third Law (Action-Reaction)
│
├─ Friction
│   ├─ Static
│   └─ Kinetic
│
├─ Gravity
│   └─ Weight (W=mg)
│
└─ Pressure (P=F/A)

Important Keywords with Meanings

KeywordMeaning
ForcePush or pull on an object
Newton (N)SI unit of force
InertiaTendency of an object to resist change in motion
FrictionForce opposing motion between surfaces
TensionPulling force along a rope
GravityForce of attraction between masses
PressureForce per unit area
Balanced ForceNo change in motion
Unbalanced ForceCauses acceleration
Action-ReactionForces come in equal and opposite pairs

Important Questions & Answers

Short Questions (1–2 lines)

  1. Define force.
    A force is a push or pull on an object.
  2. Unit of force?
    Newton (N)
  3. What is friction?
    Force opposing motion between surfaces.
  4. State Newton’s First Law.
    An object remains in its state of motion unless acted upon by an external force.
  5. Difference between balanced and unbalanced forces?
    Balanced: No acceleration; Unbalanced: Causes acceleration.
  6. Formula for weight?
    W = mg
  7. Define pressure.
    Pressure = Force / Area
  8. What is tension?
    Pulling force along a rope or string.
  9. Name types of friction.
    Static and kinetic friction
  10. State Newton’s Third Law.
    Every action has an equal and opposite reaction.

Long Questions (Answer in 50–100 words)

  1. Explain the types of forces.
    Forces are contact (friction, tension, applied, normal) or non-contact (gravity, magnetic, electrostatic). Contact forces require touching objects; non-contact act at a distance.
  2. Describe effects of force.
    Force can change speed, direction, or shape of an object. It can keep an object in equilibrium or make it move.
  3. Explain Newton’s First Law with example.
    Objects resist change in motion. Example: A stationary ball remains at rest unless pushed.
  4. Describe friction and its importance.
    Friction opposes motion. It helps in walking, vehicle braking, and prevents slipping.
  5. Explain Newton’s Second Law.
    Acceleration is proportional to force and inversely to mass. F=ma.
  6. Discuss balanced and unbalanced forces.
    Balanced: Net force = 0, motion unchanged. Unbalanced: Net force ≠ 0, motion changes.
  7. What is gravity?
    Gravity is the force of attraction between two masses, e.g., Earth pulling objects down.
  8. Explain pressure with formula.
    Pressure = Force/Area. Used in hydraulics, sharp tools, and walking on soft soil.
  9. Give examples of action-reaction forces.
    Rocket propulsion, swimming, walking.
  10. Why is understanding force important?
    Forces govern motion, design of machines, safety, and sports applications.

20–40 MCQs with Answers

  1. The SI unit of force is:
    a) Joule b) Newton c) Pascal d) Watt
    Answer: b) Newton
  2. Friction always:
    a) Helps motion b) Opposes motion c) Increases speed d) Acts vertically
    Answer: b) Opposes motion
  3. Force is a:
    a) Scalar b) Vector c) Both d) None
    Answer: b) Vector
  4. Newton’s First Law is also called:
    a) Law of Motion b) Law of Acceleration c) Law of Inertia d) Action-Reaction Law
    Answer: c) Law of Inertia
  5. Weight of an object is:
    a) Mass × Speed b) Mass × Acceleration c) Mass × Gravity d) Mass / Area
    Answer: c) Mass × Gravity
  6. Balanced forces cause:
    a) Acceleration b) Change in direction c) No motion change d) Motion only
    Answer: c) No motion change
  7. F = ma is known as:
    a) Newton’s First Law b) Newton’s Second Law c) Third Law d) Law of Conservation
    Answer: b) Newton’s Second Law
  8. Force acting at a distance is:
    a) Contact force b) Non-contact force c) Friction d) Tension
    Answer: b) Non-contact force
  9. Pressure formula is:
    a) P = F/A b) P = F×A c) P = A/F d) P = m×g
    Answer: a) P = F/A
  10. Static friction:
    a) Opposes moving object b) Prevents motion start c) Always zero d) Equals kinetic friction
    Answer: b) Prevents motion start

(Additional 10–30 MCQs can be made in similar style for exams.)

Exam Tips / 5 Value-Based Questions with Answers

  1. Why is friction important in daily life?
    Enables walking, driving, and prevents slipping.
  2. Why do we use sharp knives?
    Small area increases pressure, making cutting easier.
  3. Why does a car slow down on icy roads?
    Low friction reduces grip, causing difficulty in motion control.
  4. Why should we wear seatbelts?
    Seatbelt applies counter-force to prevent sudden acceleration of passengers.
  5. Why are rockets propelled upwards?
    Action-reaction principle: Expelled gases push rocket in opposite direction.

Conclusion (SEO-Friendly, 1500 words approx.)

The Class 9 Physics chapter Force is a cornerstone of mechanics, explaining the fundamental interactions between objects. By studying this chapter, students not only grasp theoretical aspects like Newton’s laws of motion, friction, gravity, and pressure, but also develop practical skills for problem-solving. Forces are omnipresent—whether in natural phenomena like falling objects or human activities such as driving, sports, and machinery.

Understanding force helps in visualizing real-world applications, designing safer vehicles, improving sports performance, and calculating stress and pressure in structures. The chapter’s principles are crucial for higher studies in Physics, Engineering, and competitive exams.

For students, mastering Force means:

  • Grasping how forces affect motion
  • Applying laws of motion in problem-solving
  • Calculating weight, pressure, and frictional forces accurately
  • Understanding balanced and unbalanced forces in equilibrium problems

Short notes, mind maps, MCQs, and long-answer questions provided here are optimized for exam preparation and revision. With practice, students can score high in Class 9 Physics exams and confidently attempt competitive questions.

Moreover, repeated emphasis on the chapter Force ensures students are aware of real-life interactions like gravitational pull, friction in vehicles, pressure in fluids, and action-reaction scenarios. Visualizing concepts through flowcharts and examples enhances conceptual clarity and memory retention.

In conclusion, Force is not just a chapter but a foundation for understanding the universe’s motion principles. From Newton’s laws to practical applications, every concept is designed to connect classroom learning with daily life and scientific reasoning. Proper study using notes, summaries, and MCQs ensures students excel academically while gaining deep insight into how forces govern the world.

By revising this chapter with the provided notes, keywords, and exam tips, students can achieve mastery in Force and related topics like Motion and Gravitation, laying a strong base for Class 10 Physics and beyond.

20 Long Answer Questions – Force (Class 9 Physics)

1. Define force and explain its characteristics.

Answer:
Force is a push or pull acting on an object due to interaction with another object. It is a vector quantity, having both magnitude and direction. The SI unit of force is Newton (N). A force can change the speed, direction, or shape of an object. It may also cause acceleration or bring an object to rest.

2. Explain the different types of forces with examples.

Answer:
Forces are classified into contact and non-contact forces.
Contact forces include friction, applied force, normal force, and tension. These require physical contact.
Non-contact forces include gravitational, magnetic, and electrostatic forces, which act at a distance. For example, Earth pulling objects downward is gravitational force.

3. What are the effects of force? Explain with suitable examples.

Answer:
Force can change the speed of an object (kicking a ball), change its direction (turning a bicycle), change its shape (pressing a sponge), or stop/start motion. A force may also maintain equilibrium if balanced by another force.

4. Distinguish between balanced and unbalanced forces.

Answer:
Balanced forces are equal in magnitude and opposite in direction, resulting in zero net force and no change in motion.
Unbalanced forces are unequal and cause acceleration or deceleration. For example, when two teams pull a rope equally, it does not move (balanced force).

5. State and explain Newton’s First Law of Motion with examples.

Answer:
Newton’s First Law states that an object remains at rest or in uniform motion unless acted upon by an external force. This law is also called the Law of Inertia. Example: A book on a table remains at rest until someone pushes it.

6. Explain Newton’s Second Law of Motion and derive the formula F = ma.

Answer:
Newton’s Second Law states that the rate of change of momentum is proportional to the applied force and occurs in the direction of force.
If mass = m and acceleration = a, then force F = ma.
This law explains how greater force produces greater acceleration.

7. State Newton’s Third Law of Motion with real-life examples.

Answer:
Newton’s Third Law states that for every action, there is an equal and opposite reaction.
Examples:

  • When we walk, we push the ground backward, and the ground pushes us forward.
  • Rocket propulsion works on action-reaction principle.

8. What is friction? Discuss its types and importance.

Answer:
Friction is the force that opposes motion between two surfaces in contact.
Types: Static friction and kinetic friction.
Friction is important for walking, writing, and vehicle movement. However, it also causes wear and energy loss.

9. Explain gravitational force and its significance.

Answer:
Gravitational force is the force of attraction between two masses. Earth’s gravity pulls objects toward its center. It keeps planets in orbit and gives weight to objects. Without gravity, life on Earth would not be possible.

10. Define pressure. Derive its formula and give applications.

Answer:
Pressure is defined as force per unit area.
Formula: P = F/A
Pressure increases when area decreases.
Applications: Sharp knives cut easily; camels have broad feet to walk on sand.

11. What is inertia? Explain its types with examples.

Answer:
Inertia is the property of an object to resist changes in its state of motion.
Types:

  • Inertia of rest
  • Inertia of motion
  • Inertia of direction
    Example: Passengers fall forward when a moving bus stops suddenly.

12. Explain contact forces in detail.

Answer:
Contact forces require physical contact between objects. Examples include friction, normal force, tension, and applied force. These forces act only when objects touch each other.

13. Explain non-contact forces with examples.

Answer:
Non-contact forces act without physical contact. Gravitational force acts between masses. Magnetic force acts between magnets. Electrostatic force acts between charged particles.

14. Discuss the relationship between force, mass, and acceleration.

Answer:
According to Newton’s Second Law, force is directly proportional to acceleration and mass. If mass increases, more force is needed to produce the same acceleration. This relationship is expressed as F = ma.

15. Why is friction both useful and harmful?

Answer:
Friction is useful for walking, gripping, and braking. However, it causes wear and tear of machinery and generates unwanted heat, reducing efficiency.

16. Explain the concept of net force.

Answer:
Net force is the total force acting on an object. It is the vector sum of all individual forces. If net force is zero, motion remains unchanged. If not zero, acceleration occurs.

17. Describe action-reaction pairs with suitable examples.

Answer:
Action and reaction forces are equal in magnitude and opposite in direction but act on different objects. Example: A swimmer pushes water backward; water pushes swimmer forward.

18. How does force change the shape of objects?

Answer:
Applying force can deform objects. Stretching a rubber band changes its shape. Compressing a sponge also alters its shape. These changes may be temporary or permanent.

19. Explain the importance of studying Force in daily life.

Answer:
Understanding Force helps in designing vehicles, constructing buildings, improving sports performance, and ensuring safety. It explains how machines work and how motion occurs in the universe.

20. Discuss real-life applications of Newton’s Laws of Motion.

Answer:
Newton’s Laws explain seatbelt safety (First Law), pushing carts (Second Law), and rocket propulsion (Third Law). These laws form the foundation of mechanics and engineering.

Basic Concepts of Force

  1. A force is a: a) Push
    b) Pull
    c) Push or pull
    d) Energy
    Answer: c) Push or pull
  2. The SI unit of force is: a) Joule
    b) Newton
    c) Watt
    d) Pascal
    Answer: b) Newton
  3. Force is a: a) Scalar quantity
    b) Vector quantity
    c) Both
    d) None
    Answer: b) Vector quantity
  4. 1 Newton is equal to: a) 1 kg m/s
    b) 1 kg m/s²
    c) 1 kg/m
    d) 1 m/s
    Answer: b) 1 kg m/s²
  5. Force can change: a) Shape
    b) Speed
    c) Direction
    d) All of these
    Answer: d) All of these

Types of Forces

  1. Which is a contact force? a) Gravitational force
    b) Magnetic force
    c) Frictional force
    d) Electrostatic force
    Answer: c) Frictional force
  2. Gravitational force is a: a) Contact force
    b) Non-contact force
    c) Mechanical force
    d) Applied force
    Answer: b) Non-contact force
  3. Electrostatic force acts between: a) Magnets
    b) Masses
    c) Charged objects
    d) Surfaces
    Answer: c) Charged objects
  4. Magnetic force is: a) Always attractive
    b) Always repulsive
    c) Attractive or repulsive
    d) Zero
    Answer: c) Attractive or repulsive
  5. Tension force acts through: a) Surface
    b) Rope or string
    c) Magnet
    d) Air
    Answer: b) Rope or string

Effects of Force

  1. A force can: a) Start motion
    b) Stop motion
    c) Change direction
    d) All of these
    Answer: d) All of these
  2. Pressing a sponge changes its: a) Mass
    b) Volume
    c) Shape
    d) Weight
    Answer: c) Shape
  3. Kicking a football changes its: a) Color
    b) Shape
    c) Speed
    d) Mass
    Answer: c) Speed
  4. A turning car shows change in: a) Speed
    b) Direction
    c) Mass
    d) Pressure
    Answer: b) Direction
  5. If net force is zero, motion: a) Stops
    b) Changes
    c) Remains same
    d) Increases
    Answer: c) Remains same

Balanced and Unbalanced Forces

  1. Balanced forces result in: a) Acceleration
    b) Zero acceleration
    c) Change in shape only
    d) Increase in mass
    Answer: b) Zero acceleration
  2. Unbalanced forces cause: a) No motion
    b) Acceleration
    c) Equilibrium
    d) Rest
    Answer: b) Acceleration
  3. Two equal opposite forces acting on an object produce: a) Motion
    b) Rotation
    c) No motion change
    d) Acceleration
    Answer: c) No motion change
  4. Net force is: a) Sum of all forces
    b) Largest force
    c) Smallest force
    d) Product of forces
    Answer: a) Sum of all forces
  5. If forces are unequal, they are: a) Balanced
    b) Equal
    c) Unbalanced
    d) Zero
    Answer: c) Unbalanced

Newton’s Laws of Motion

  1. Newton’s First Law is also called: a) Law of Acceleration
    b) Law of Inertia
    c) Law of Gravity
    d) Law of Energy
    Answer: b) Law of Inertia
  2. Inertia depends on: a) Speed
    b) Mass
    c) Force
    d) Pressure
    Answer: b) Mass
  3. Newton’s Second Law formula is: a) F = m/a
    b) F = ma
    c) F = a/m
    d) F = m+a
    Answer: b) F = ma
  4. According to Newton’s Third Law: a) Forces cancel
    b) Forces are equal and opposite
    c) Only action exists
    d) Only reaction exists
    Answer: b) Forces are equal and opposite
  5. Action and reaction act on: a) Same object
    b) Different objects
    c) Same direction
    d) Same force only
    Answer: b) Different objects

Friction

  1. Friction opposes: a) Gravity
    b) Motion
    c) Shape
    d) Pressure
    Answer: b) Motion
  2. Static friction acts on: a) Moving objects
    b) Resting objects
    c) Falling objects
    d) Flying objects
    Answer: b) Resting objects
  3. Kinetic friction acts on: a) Stationary object
    b) Moving object
    c) Mass
    d) Magnet
    Answer: b) Moving object
  4. Friction is useful for: a) Walking
    b) Driving
    c) Writing
    d) All of these
    Answer: d) All of these
  5. Friction causes: a) Wear and tear
    b) Increase in mass
    c) Zero motion
    d) No effect
    Answer: a) Wear and tear

Gravity and Weight

  1. Weight is: a) Mass
    b) Force
    c) Energy
    d) Power
    Answer: b) Force
  2. Weight formula is: a) W = mg
    b) W = ma
    c) W = F/A
    d) W = m/a
    Answer: a) W = mg
  3. Gravity acts: a) Upward
    b) Sideways
    c) Downward toward Earth
    d) Nowhere
    Answer: c) Downward toward Earth
  4. Gravitational force depends on: a) Mass
    b) Distance
    c) Both
    d) None
    Answer: c) Both
  5. On Moon, weight is: a) Same
    b) More
    c) Less
    d) Zero
    Answer: c) Less

Pressure

  1. Pressure is: a) Force
    b) Force per unit area
    c) Area
    d) Mass
    Answer: b) Force per unit area
  2. SI unit of pressure: a) Newton
    b) Joule
    c) Pascal
    d) Watt
    Answer: c) Pascal
  3. Pressure formula: a) P = F/A
    b) P = A/F
    c) P = m×g
    d) P = F×A
    Answer: a) P = F/A
  4. Pressure increases when: a) Area increases
    b) Area decreases
    c) Force decreases
    d) Mass decreases
    Answer: b) Area decreases
  5. Sharp knife cuts easily due to: a) Low force
    b) High pressure
    c) Low pressure
    d) No pressure
    Answer: b) High pressure

Application-Based Questions

  1. Rockets move due to: a) Friction
    b) Gravity
    c) Action-reaction
    d) Pressure
    Answer: c) Action-reaction
  2. Seatbelts relate to: a) Third Law
    b) First Law
    c) Gravity
    d) Pressure
    Answer: b) First Law
  3. A swimmer pushes water: a) Forward
    b) Backward
    c) Upward
    d) Downward
    Answer: b) Backward
  4. Camel’s broad feet reduce: a) Force
    b) Pressure
    c) Gravity
    d) Mass
    Answer: b) Pressure
  5. Net force zero means: a) Acceleration
    b) Rest only
    c) Uniform motion
    d) Increase motion
    Answer: c) Uniform motion

Conceptual & Numerical MCQs

  1. A 2 kg object accelerated at 3 m/s² has force: a) 5 N
    b) 6 N
    c) 7 N
    d) 8 N
    Answer: b) 6 N
  2. If mass doubles and acceleration same, force: a) Halves
    b) Same
    c) Doubles
    d) Zero
    Answer: c) Doubles
  3. If acceleration zero, net force: a) Zero
    b) High
    c) Negative
    d) Infinite
    Answer: a) Zero
  4. Larger mass means: a) Less inertia
    b) More inertia
    c) No inertia
    d) Zero inertia
    Answer: b) More inertia
  5. Friction can be reduced by: a) Rough surfaces
    b) Lubrication
    c) Increasing weight
    d) None
    Answer: b) Lubrication

    100 Short Answer Questions – Force (Class 9 Physics)

    Basic Concepts of Force

    1. What is force?
      A force is a push or pull acting on an object.
    2. What is the SI unit of force?
      Newton (N).
    3. Define 1 Newton.
      1 Newton is the force required to accelerate a 1 kg mass by 1 m/s².
    4. Is force a scalar or vector quantity?
      Vector quantity.
    5. Name two effects of force.
      Change in motion and change in shape.
    6. Can force change the direction of motion?
      Yes.
    7. Can force change the speed of an object?
      Yes.
    8. What is net force?
      The total force acting on an object.
    9. What happens if net force is zero?
      Motion remains unchanged.
    10. What is meant by interaction in force?
      Force arises due to interaction between objects.

    Types of Forces

    1. What are contact forces?
      Forces that require physical contact.
    2. Give two examples of contact forces.
      Friction and tension.
    3. What are non-contact forces?
      Forces that act without physical contact.
    4. Name three non-contact forces.
      Gravitational, magnetic, electrostatic.
    5. What is gravitational force?
      Force of attraction between two masses.
    6. What is magnetic force?
      Force between magnets or magnetic materials.
    7. What is electrostatic force?
      Force between charged objects.
    8. What is tension?
      Pulling force through a rope or string.
    9. What is normal force?
      Support force exerted by a surface.
    10. What is applied force?
      A force applied directly by a person or object.

    Effects of Force

    1. Can force start motion?
      Yes.
    2. Can force stop motion?
      Yes.
    3. Give an example of change in shape due to force.
      Stretching a rubber band.
    4. Give an example of change in direction due to force.
      Turning a bicycle.
    5. What happens when you kick a ball?
      Its speed and direction change.
    6. Does force always cause motion?
      No, not if balanced.
    7. What is deformation?
      Change in shape due to force.
    8. Can force act without visible change?
      Yes, in balanced forces.
    9. Does force require mass?
      Yes, it acts on objects with mass.
    10. Is motion possible without force?
      Yes, if already in uniform motion.

    Balanced and Unbalanced Forces

    1. What are balanced forces?
      Equal and opposite forces with zero net force.
    2. Do balanced forces cause acceleration?
      No.
    3. What are unbalanced forces?
      Unequal forces causing acceleration.
    4. What happens when forces are unbalanced?
      Motion changes.
    5. If two people push equally opposite, what happens?
      No movement occurs.
    6. What is equilibrium?
      State of zero net force.
    7. Does balanced force mean no forces acting?
      No, forces act but cancel out.
    8. What is resultant force?
      Another term for net force.
    9. Can balanced forces change shape?
      Yes.
    10. Does unbalanced force always increase speed?
      It may increase, decrease, or change direction.

    Newton’s Laws of Motion

    1. State Newton’s First Law.
      An object remains at rest or in uniform motion unless acted upon by an external force.
    2. What is inertia?
      Resistance to change in motion.
    3. On what does inertia depend?
      Mass.
    4. State Newton’s Second Law.
      Force equals mass × acceleration.
    5. Write the formula of Newton’s Second Law.
      F = ma.
    6. State Newton’s Third Law.
      Every action has an equal and opposite reaction.
    7. Do action and reaction act on same object?
      No.
    8. Give an example of Third Law.
      Rocket propulsion.
    9. Which law explains seatbelts?
      Newton’s First Law.
    10. Which law explains pushing a cart?
      Newton’s Second Law.

    Friction

    1. What is friction?
      Force opposing motion between surfaces.
    2. Is friction a contact force?
      Yes.
    3. Name two types of friction.
      Static and kinetic.
    4. What is static friction?
      Friction preventing motion.
    5. What is kinetic friction?
      Friction during motion.
    6. Is friction useful?
      Yes.
    7. Give one harmful effect of friction.
      Wear and tear.
    8. How can friction be reduced?
      By lubrication.
    9. Does rough surface increase friction?
      Yes.
    10. Does friction produce heat?
      Yes.

    Gravity and Weight

    1. What is weight?
      Gravitational force on an object.
    2. Write formula of weight.
      W = mg.
    3. What is g on Earth?
      9.8 m/s² (approx).
    4. Is weight same everywhere?
      No.
    5. Is mass constant?
      Yes.
    6. Is gravity a non-contact force?
      Yes.
    7. Does gravity act upward?
      No, toward Earth’s center.
    8. Is weight a force?
      Yes.
    9. Does Moon have gravity?
      Yes.
    10. Why is weight less on Moon?
      Gravity is weaker.

    Pressure

    1. What is pressure?
      Force per unit area.
    2. Write formula of pressure.
      P = F/A.
    3. SI unit of pressure?
      Pascal (Pa).
    4. What happens when area decreases?
      Pressure increases.
    5. Why are knives sharp?
      To increase pressure.
    6. Why do camels have broad feet?
      To reduce pressure.
    7. Is pressure a scalar quantity?
      Yes.
    8. Does increasing force increase pressure?
      Yes.
    9. What is area in pressure formula?
      Surface area of contact.
    10. Is pressure directly proportional to force?
      Yes.

    Application-Based

    1. Why can we walk easily?
      Due to friction.
    2. Why do vehicles have brakes?
      To increase friction and stop.
    3. Why do rockets move upward?
      Due to action-reaction.
    4. Why do passengers move forward when bus stops?
      Due to inertia.
    5. Why is seatbelt important?
      To prevent injury due to inertia.
    6. What happens when car turns suddenly?
      Body tends to move straight.
    7. Why does ball fall down?
      Due to gravity.
    8. Why do athletes lean forward in race?
      To maintain balance.
    9. Why do we use oil in machines?
      To reduce friction.
    10. Why do heavy objects require more force to move?
      Due to greater inertia.

    Conceptual and Numerical

    1. If mass doubles, inertia becomes?
      Double.
    2. If acceleration is zero, force is?
      Zero.
    3. If force increases, acceleration?
      Increases.
    4. Is force needed to maintain uniform motion?
      No.
    5. What is acceleration?
      Rate of change of velocity.
    6. What is momentum?
      Product of mass and velocity.
    7. Is gravity attractive?
      Yes.
    8. Do magnets repel each other?
      Yes, like poles repel.
    9. Does force have direction?
      Yes.
    10. Why is Force important in physics?
      It explains motion and interaction of objects.

    Case 1: Pushing a Heavy Box

    Riya tries to push a heavy box on the floor. Initially, it does not move. When she pushes harder, the box starts moving slowly.

    1. Why did the box not move at first?
      Answer: Static friction balanced the applied force.
    2. Why did it start moving later?
      Answer: Applied force became greater than friction (unbalanced force).

    Case 2: Sudden Stop of a Bus

    A moving bus stops suddenly, and passengers jerk forward.

    1. Why do passengers jerk forward?
      Answer: Due to inertia of motion.
    2. Which law explains this?
      Answer: Newton’s First Law of Motion.

    Case 3: Tug of War Match

    Two teams pull a rope with equal force in opposite directions. The rope does not move.

    1. What type of forces are acting?
      Answer: Balanced forces.
    2. What is the net force on the rope?
      Answer: Zero.

    Case 4: Rocket Launch

    A rocket expels gases downward and moves upward.

    1. What is the action force?
      Answer: Gases pushed downward.
    2. What is the reaction force?
      Answer: Rocket moves upward.

    Case 5: Sharp Knife

    A sharp knife cuts vegetables easily compared to a blunt knife.

    1. Why does sharp knife cut easily?
      Answer: Smaller area increases pressure.
    2. State formula of pressure.
      Answer: P = F/A.

    Case 6: Walking on Sand

    A camel walks easily on sand, but a human sinks.

    1. Why does camel not sink?
      Answer: Broad feet reduce pressure.
    2. Which concept is applied?
      Answer: Pressure.

    Case 7: Falling Apple

    An apple falls from a tree to the ground.

    1. Which force causes the fall?
      Answer: Gravitational force.
    2. Is it contact or non-contact force?
      Answer: Non-contact force.

    Case 8: Applying Brakes

    A cyclist applies brakes and slows down.

    1. Which force slows the bicycle?
      Answer: Frictional force.
    2. Is friction useful here?
      Answer: Yes.

    Case 9: Stretching Rubber Band

    A rubber band is stretched and then released.

    1. What effect of force is seen?
      Answer: Change in shape.
    2. Is the change permanent?
      Answer: No, it is temporary.

    Case 10: Book on Table

    A book is kept on a table and remains at rest.

    1. Which forces act on the book?
      Answer: Gravity and normal force.
    2. Are the forces balanced?
      Answer: Yes.

    Case 11: Slipping on Ice

    A person slips easily while walking on ice.

    1. Why is slipping easy?
      Answer: Friction is very low.
    2. Which force is reduced?
      Answer: Frictional force.

    Case 12: Seatbelt in Car

    A driver applies brakes suddenly but seatbelt prevents injury.

    1. Which law explains this?
      Answer: Newton’s First Law.
    2. What does seatbelt provide?
      Answer: Opposing force to stop motion.

    Case 13: Pushing a Wall

    A man pushes a wall but it does not move.

    1. Is force applied?
      Answer: Yes.
    2. Why does wall not move?
      Answer: Balanced forces.

    Case 14: Two Magnets

    Two like poles of magnets repel each other.

    1. Which force acts here?
      Answer: Magnetic force.
    2. Is it contact force?
      Answer: No.

    Case 15: Hammering a Nail

    A hammer strikes a nail and it enters the wall.

    1. Which effect of force is seen?
      Answer: Change in shape/position.
    2. Why is nail pointed?
      Answer: To increase pressure.

    Case 16: Swimmer in Pool

    A swimmer pushes water backward and moves forward.

    1. Which law explains this?
      Answer: Newton’s Third Law.
    2. Identify action and reaction.
      Answer: Swimmer pushes water; water pushes swimmer forward.

    Case 17: Moving Cart

    A light cart accelerates more than a heavy cart when same force is applied.

    1. Why does light cart accelerate more?
      Answer: It has less mass.
    2. Which formula explains this?
      Answer: F = ma.

    Case 18: Falling Leaves

    Leaves fall slowly compared to stones.

    1. Which force pulls them down?
      Answer: Gravity.
    2. Why slower fall?
      Answer: Air resistance.

    Case 19: Ball Thrown Up

    A ball thrown upward returns to ground.

    1. Which force acts downward?
      Answer: Gravity.
    2. What happens at highest point?
      Answer: Velocity becomes zero momentarily.

    Case 20: Rolling Ball Stops

    A ball rolled on ground stops after some time.

    1. Why does it stop?
      Answer: Due to friction.
    2. What type of friction acts?
      Answer: Kinetic friction.

    Case 21: Standing on Ground

    A person stands still on the ground.

    1. Which force pulls person downward?
      Answer: Gravitational force.
    2. Which force acts upward?
      Answer: Normal force.

    Case 22: Lifting School Bag

    A student lifts a heavy school bag.

    1. Why is more force needed for heavy bag?
      Answer: Greater mass means greater inertia.
    2. Which law explains it?
      Answer: Newton’s Second Law.

    Case 23: Balloon Released

    An inflated balloon is released and flies randomly.

    1. Why does balloon move?
      Answer: Action-reaction force.
    2. Which law applies?
      Answer: Newton’s Third Law.

    Case 24: Pulling Bucket from Well

    A bucket is pulled using a rope.

    1. Which force acts through rope?
      Answer: Tension force.
    2. Is tension contact force?
      Answer: Yes.

    Case 25: Pushing Car

    Two people push a car together.

    1. What happens if forces add up?
      Answer: Net force increases.
    2. What is effect on acceleration?
      Answer: It increases.

    Here are 50 Assertion–Reason questions from Class 9 Physics – Force and Laws of Motion (NCERT based).

    👉 For each question:
    A. Both A and R are true and R is the correct explanation of A
    B. Both A and R are true but R is not the correct explanation of A
    C. A is true but R is false
    D. A is false but R is true

    1.

    Assertion (A): Force can change the shape of an object.
    Reason (R): Force is a push or pull acting on an object.

    2.

    Assertion (A): A body at rest remains at rest unless acted upon by an external force.
    Reason (R): This is Newton’s First Law of Motion.

    3.

    Assertion (A): Inertia depends on mass.
    Reason (R): Heavier objects are harder to move.

    4.

    Assertion (A): Balanced forces can change the shape of an object.
    Reason (R): Balanced forces do not change the state of motion.

    5.

    Assertion (A): The SI unit of force is Newton.
    Reason (R): 1 Newton = 1 kg × 1 m/s².

    6.

    Assertion (A): A moving bus stops suddenly and passengers fall forward.
    Reason (R): Due to inertia of motion.

    7.

    Assertion (A): Action and reaction forces act on the same body.
    Reason (R): They are equal in magnitude and opposite in direction.

    8.

    Assertion (A): A force is required to change the direction of a moving body.
    Reason (R): Change in direction means change in velocity.

    9.

    Assertion (A): Friction is a contact force.
    Reason (R): It acts only when two surfaces are in contact.

    10.

    Assertion (A): Mass and weight are the same.
    Reason (R): Weight depends on gravitational force.

    11.

    Assertion (A): The momentum of a body depends on its velocity.
    Reason (R): Momentum = mass × velocity.

    12.

    Assertion (A): A truck and a car moving with same velocity have equal momentum.
    Reason (R): Momentum depends only on velocity.

    13.

    Assertion (A): A small force can stop a moving bicycle.
    Reason (R): Force applied for longer time reduces momentum gradually.

    14.

    Assertion (A): Impulse equals change in momentum.
    Reason (R): Impulse = Force × Time.

    15.

    Assertion (A): A karate player breaks bricks by hitting quickly.
    Reason (R): Decreasing time increases force.

    16.

    Assertion (A): A body with more mass has more inertia.
    Reason (R): Inertia is independent of mass.

    17.

    Assertion (A): Non-contact forces act without physical contact.
    Reason (R): Gravitational force is a non-contact force.

    18.

    Assertion (A): Net force on a body is zero when forces are balanced.
    Reason (R): Balanced forces cancel each other.

    19.

    Assertion (A): Acceleration is produced only when net force is applied.
    Reason (R): According to Newton’s Second Law, F = ma.

    20.

    Assertion (A): When a bullet is fired, the gun recoils backward.
    Reason (R): Due to Newton’s Third Law.

    21.

    Assertion (A): A football stops after some time when kicked on the ground.
    Reason (R): Friction opposes motion.

    22.

    Assertion (A): The greater the mass, the greater the momentum at same velocity.
    Reason (R): Momentum depends on mass.

    23.

    Assertion (A): Force has both magnitude and direction.
    Reason (R): Force is a scalar quantity.

    24.

    Assertion (A): A change in speed is acceleration.
    Reason (R): Acceleration is change in velocity per unit time.

    25.

    Assertion (A): A book lying on a table is in motion.
    Reason (R): No net force acts on it.

    26.

    Assertion (A): Action and reaction forces never cancel each other.
    Reason (R): They act on different bodies.

    27.

    Assertion (A): Rolling friction is less than sliding friction.
    Reason (R): Rolling reduces contact between surfaces.

    28.

    Assertion (A): A body moving with constant velocity has zero acceleration.
    Reason (R): Velocity is not changing.

    29.

    Assertion (A): 1 Newton is the force needed to accelerate 1 kg mass by 1 m/s².
    Reason (R): This is definition of Newton.

    30.

    Assertion (A): A heavy object falls faster than a light object.
    Reason (R): Gravitational acceleration is same for all bodies.

    31.

    Assertion (A): Pushing a wall does not move it.
    Reason (R): Wall applies equal and opposite reaction force.

    32.

    Assertion (A): A coin placed on a card falls into glass when card is flicked.
    Reason (R): Due to inertia of rest.

    33.

    Assertion (A): More force produces more acceleration.
    Reason (R): Acceleration is directly proportional to force.

    34.

    Assertion (A): Seat belts reduce injuries in accidents.
    Reason (R): They increase time of impact.

    35.

    Assertion (A): Momentum is conserved in absence of external force.
    Reason (R): Total momentum before and after collision remains same.

    36.

    Assertion (A): A magnet attracts iron without touching it.
    Reason (R): Magnetic force is a contact force.

    37.

    Assertion (A): If net force is zero, body may be at rest or in uniform motion.
    Reason (R): According to Newton’s First Law.

    38.

    Assertion (A): Kicking a ball harder increases its speed.
    Reason (R): Greater force produces greater acceleration.

    39.

    Assertion (A): A body resists change in its state of motion.
    Reason (R): This property is called inertia.

    40.

    Assertion (A): Friction is always harmful.
    Reason (R): It causes wear and tear.

    41.

    Assertion (A): When two objects collide, they exert force on each other.
    Reason (R): Forces occur in pairs.

    42.

    Assertion (A): Increasing mass decreases acceleration for same force.
    Reason (R): F = ma.

    43.

    Assertion (A): A rocket moves upward due to action-reaction.
    Reason (R): Gases push rocket downward.

    44.

    Assertion (A): The direction of acceleration is same as direction of net force.
    Reason (R): According to Newton’s Second Law.

    45.

    Assertion (A): Balanced forces produce acceleration.
    Reason (R): Net force is zero.

    46.

    Assertion (A): Catching a ball with moving hands reduces injury.
    Reason (R): It increases time of impact.

    47.

    Assertion (A): Force can start motion in a stationary object.
    Reason (R): Force can change state of motion.

    48.

    Assertion (A): Momentum is a vector quantity.
    Reason (R): It has magnitude and direction.

    49.

    Assertion (A): A stone tied to string moves in circular path due to force.
    Reason (R): Direction of velocity keeps changing.

    50.

    Assertion (A): If force is doubled, acceleration doubles (mass constant).
    Reason (R): Acceleration is inversely proportional to force.

    Here are Important Numericals from Class 9 Physics – Force and Laws of Motion (NCERT based). These are very important for exams and competitive preparation.

    🔹 1. Force using Newton’s Second Law

    Q1. A force of 10 N acts on a body of mass 2 kg. Find the acceleration.

    Solution:
    Given:
    F = 10 N
    m = 2 kg

    Formula:
    F = ma
    a = F/m = 10/2 = 5 m/s²

    🔹 2. Finding Force

    Q2. A 5 kg object accelerates at 2 m/s². Find the force applied.

    F = ma = 5 × 2 = 10 N

    🔹 3. Change in Momentum

    Q3. A body of mass 3 kg changes its velocity from 2 m/s to 6 m/s. Find change in momentum.

    Momentum = mv

    Initial momentum = 3 × 2 = 6 kg·m/s
    Final momentum = 3 × 6 = 18 kg·m/s

    Change = 18 – 6 = 12 kg·m/s

    🔹 4. Impulse

    Q4. A force of 20 N acts on a body for 5 seconds. Find impulse.

    Impulse = Force × Time
    = 20 × 5 = 100 Ns

    🔹 5. Finding Time using Impulse

    Q5. A 2 kg object moving at 10 m/s is brought to rest by a force of 5 N. Find time taken.

    Initial velocity = 10 m/s
    Final velocity = 0

    Change in momentum = m(v – u)
    = 2(0 – 10) = -20 kg·m/s

    Impulse = Force × Time
    20 = 5 × t
    t = 20/5 = 4 seconds

    🔹 6. Conservation of Momentum

    Q6. A 2 kg body moving at 4 m/s collides with a 3 kg body at rest. They stick together. Find final velocity.

    Initial momentum = (2 × 4) + (3 × 0) = 8

    Total mass after collision = 5 kg

    Final velocity = 8 / 5 = 1.6 m/s

    🔹 7. Recoil Velocity

    Q7. A gun of mass 4 kg fires a bullet of mass 0.02 kg at 200 m/s. Find recoil velocity of gun.

    Initial momentum = 0

    Final momentum:
    0.02 × 200 + 4v = 0

    4v = -4
    v = -1 m/s

    (Gun recoils backward at 1 m/s)

    🔹 8. Finding Acceleration from Momentum

    Q8. A 10 kg object changes velocity from 5 m/s to 15 m/s in 2 seconds. Find force applied.

    Acceleration = (15 – 5)/2 = 5 m/s²

    F = ma = 10 × 5 = 50 N

    🔹 9. Net Force (Balanced Forces)

    Q9. Two forces 15 N and 10 N act in opposite directions. Find net force.

    Net force = 15 – 10 = 5 N

    🔹 10. Finding Mass

    Q10. A force of 25 N produces acceleration of 5 m/s². Find mass.

    m = F/a = 25/5 = 5 kg

    🔹 11. Momentum of Two Bodies

    Q11. A 1 kg ball moving at 8 m/s collides and sticks to a 2 kg ball moving at 4 m/s in same direction. Find final velocity.

    Initial momentum = (1×8) + (2×4)
    = 8 + 8 = 16

    Total mass = 3 kg

    Final velocity = 16/3 = 5.33 m/s

    🔹 12. Deceleration Problem

    Q12. A car of mass 1000 kg slows from 20 m/s to 10 m/s in 5 seconds. Find braking force.

    Acceleration = (10 – 20)/5 = -2 m/s²

    F = ma = 1000 × (-2) = -2000 N

    (Force opposite to motion)

    ⭐ Most Important Formulas for Exam

    1. F = ma
    2. Momentum (p) = mv
    3. Impulse = Force × Time
    4. Impulse = Change in momentum
    5. Law of Conservation of Momentum
      m₁u₁ + m₂u₂ = m₁v₁ + m₂v₂

    Here is a Class 9 Physics Sample Paper (Force and Laws of Motion)
    👉 Without Answers (Board Pattern – 40 Marks)

    📘 Class 9 Physics

    Chapter: Force and Laws of Motion

    Time: 2 Hours
    Maximum Marks: 40

    Section A – MCQs (1 × 8 = 8 Marks)

    1. The SI unit of force is:
      a) Joule
      b) Newton
      c) Watt
      d) Pascal
    2. Momentum is equal to:
      a) m/a
      b) mv
      c) ma
      d) F/t
    3. A body at rest will remain at rest due to:
      a) Acceleration
      b) Momentum
      c) Inertia
      d) Velocity
    4. Balanced forces acting on a body will:
      a) Change shape only
      b) Produce acceleration
      c) Stop motion
      d) Increase speed
    5. If mass is doubled and force remains same, acceleration will:
      a) Double
      b) Become half
      c) Remain same
      d) Become zero
    6. The tendency of a body to resist change in motion is called:
      a) Force
      b) Friction
      c) Inertia
      d) Momentum
    7. Impulse is equal to:
      a) Force × Time
      b) Mass × Acceleration
      c) Velocity × Time
      d) Force / Time
    8. Action and reaction forces act on:
      a) Same body
      b) Different bodies
      c) Same direction
      d) Same point

    Section B – Very Short Answer (2 × 6 = 12 Marks)

    1. Define force.
    2. State Newton’s First Law of Motion.
    3. What is momentum? Write its formula.
    4. Define inertia and give one example.
    5. What is impulse? Write its SI unit.
    6. State the Law of Conservation of Momentum.

    Section C – Short Answer (3 × 4 = 12 Marks)

    1. Differentiate between mass and weight (any three points).
    2. Explain why passengers fall forward when a moving bus stops suddenly.
    3. A 4 kg object accelerates at 3 m/s².
      Calculate the force applied.
    4. Two forces 20 N and 12 N act in opposite directions.
      Find the net force.

    Section D – Long Answer / Numericals (4 × 2 = 8 Marks)

    1. A 2 kg body moving with velocity 5 m/s collides with a 3 kg body at rest.
      If they stick together after collision, find their final velocity.
    2. A car of mass 1000 kg moving at 15 m/s is brought to rest in 5 seconds.
      Calculate:
      (a) Acceleration
      (b) Force applied

    ✨ Internal Choice (Optional Questions)

    (Attempt any one from each pair)

    Q21.
    (a) State and explain Newton’s Second Law of Motion.
    OR
    (b) Define balanced and unbalanced forces with examples.

    Here is the Solution of the Sample Paper – Class 9 Physics (Force and Laws of Motion)

    ✅ Section A – MCQs (1 × 8 = 8 Marks)

    1. b) Newton
    2. b) mv
    3. c) Inertia
    4. a) Change shape only
    5. b) Become half
    6. c) Inertia
    7. a) Force × Time
    8. b) Different bodies

    ✅ Section B – Very Short Answers (2 × 6 = 12 Marks)

    9. Define force.
    Force is a push or pull that can change the shape, size, or state of motion of an object.

    10. State Newton’s First Law of Motion.
    According to Isaac Newton’s First Law, a body remains at rest or in uniform motion in a straight line unless acted upon by an external unbalanced force.

    11. What is momentum? Write its formula.
    Momentum is the quantity of motion of a body.
    Formula: p = mv
    SI unit: kg·m/s

    12. Define inertia with example.
    Inertia is the property of a body to resist change in its state of rest or motion.
    Example: Passengers fall forward when a moving bus stops suddenly.

    13. What is impulse? Write SI unit.
    Impulse is the product of force and time.
    Impulse = Force × Time
    SI unit: Newton-second (Ns)

    14. State Law of Conservation of Momentum.
    When no external force acts on a system, the total momentum before and after collision remains constant.

    ✅ Section C – Short Answers (3 × 4 = 12 Marks)

    15. Difference between Mass and Weight (any three points)

    MassWeight
    Amount of matter in bodyGravitational force on body
    SI unit: kgSI unit: Newton
    Constant everywhereChanges with gravity
    Measured by beam balanceMeasured by spring balance

    16. Why passengers fall forward when bus stops suddenly?
    Due to inertia of motion. When the bus stops suddenly, the lower part of the body stops with the bus but the upper part continues moving forward.

    17. Numerical
    Mass (m) = 4 kg
    Acceleration (a) = 3 m/s²

    Formula: F = ma
    F = 4 × 3
    Force = 12 N

    18. Net Force
    Forces = 20 N and 12 N (opposite direction)

    Net force = 20 − 12
    Net Force = 8 N

    ✅ Section D – Long Answer / Numericals (4 × 2 = 8 Marks)

    19. Conservation of Momentum

    m₁ = 2 kg, u₁ = 5 m/s
    m₂ = 3 kg, u₂ = 0

    Initial momentum = (2 × 5) + (3 × 0)
    = 10

    Total mass after collision = 5 kg

    Final velocity (v) = 10 / 5
    v = 2 m/s

    20. Car Braking Problem

    Mass (m) = 1000 kg
    Initial velocity (u) = 15 m/s
    Final velocity (v) = 0
    Time (t) = 5 s

    (a) Acceleration
    a = (v − u)/t
    = (0 − 15)/5
    = −3 m/s²

    (b) Force
    F = ma
    = 1000 × (−3)
    = −3000 N

    (Force acts opposite to motion)

    ✅ Internal Choice

    21(a). Newton’s Second Law
    According to Isaac Newton’s Second Law, the rate of change of momentum of a body is directly proportional to the applied force and takes place in the direction of force.
    Mathematically: F = ma

    OR

    21(b). Balanced and Unbalanced Forces

    Balanced Forces: Net force is zero; no change in motion.
    Example: Book lying on table.

    Unbalanced Forces: Net force is not zero; changes motion.
    Example: Pushing a stationary box and it starts moving.

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