Class 9 Physics Chapter 3 Notes – Dynamics (2026 New Syllabus)

Chapter 3 Dynamics is one of the most important chapters in Class 9 Physics. It explains how and why objects move when a force acts on them. In this chapter, students learn the basic principles that control motion in the physical world. These concepts help us understand many everyday activities such as pushing a door, riding a bicycle, or applying brakes to stop a car.

In this chapter, you will study important topics including the concept of force, the fundamental forces of nature, Newton’s Laws of Motion, the difference between mass and weight, and the role of friction. These topics form the foundation for understanding motion and are very important for exams as well as future physics studies.

The notes provided here follow the Class 9 Physics 2026 syllabus and are written in a clear and simple way so students can easily understand the concepts and prepare effectively for their exams.

Class 9 Physics Chapter 3 MCQs – Dynamics

1. Which of the following is a correct example of a force?

(a) Heat
(b) Sound
(c) Push or Pull ✅
(d) Light

2. A force that resists motion when two surfaces come in contact is called:

(a) Thrust
(b) Tension
(c) Friction ✅
(d) Normal Force

3. Which force is responsible for keeping planets in orbit around the Sun?

(a) Electrostatic force
(b) Gravitational force ✅
(c) Magnetic force
(d) Thrust

4. Newton’s First Law of Motion is also known as:

(a) Law of force
(b) Law of gravity
(c) Law of inertia ✅
(d) Law of energy

5. Newton’s Second Law of Motion is mathematically written as:

(a) F = m/v
(b) F = v/a
(c) F = ma ✅
(d) F = a/m

6. The unit 1 N (Newton) is equal to:

(a) 1 kg·m/s² ✅
(b) 1 kg/s²
(c) 1 m/kg
(d) 1 J/s

7. The correct formula to calculate weight is:

(a) w = m/v
(b) w = mg ✅
(c) w = m + g
(d) w = m × a²

8. Impulse of a force is defined as:

(a) Force × displacement
(b) Force × time interval ✅
(c) Mass × velocity
(d) Velocity / time

Class 9 Physics Chapter 3 Short Questions – Dynamics

1. What kind of changes in motion may be produced by a force?

Answer:
A force can produce several changes in the motion of an object, including:

• Start a stationary object – A force can make an object at rest begin to move.

• Stop a moving object – A force can bring a moving object to rest.

• Change the speed of an object – A force can increase or decrease the speed of an object.

• Change the direction of motion – A force can alter the path or direction in which an object is moving.

• Change the shape of an object – A force can deform an object, like stretching, compressing, or bending it.

2. Give 5 examples of contact forces.

Answer:
Contact forces are forces that act when two objects are physically touching each other. Examples include:

1. Frictional Force – The force that opposes motion between two surfaces in contact.

2. Tension in a Rope – The pulling force transmitted through a rope, string, or cable.

3. Normal Reaction Force – The perpendicular force exerted by a surface to support the weight of an object.

4. Air Resistance – The resistive force experienced by objects moving through air.

5. Applied Force by Hand or Machine – Any push or pull applied directly to an object.

3. What is meant by force?

Answer:
A force is a push or pull that can start, stop, or change the motion of a body. It can also change the shape of an object.

Explanation:
Force is a fundamental concept in physics. It is responsible for any change in the motion or deformation of objects. Forces can act in different directions and can be applied by contact (like pushing a box) or at a distance (like gravity).

4. What is drag force?

Answer:
Drag is a resistive force that acts opposite to the direction of motion of an object moving through a fluid, such as air or water.

Explanation:
Drag force slows down moving objects in fluids. For example, air resistance slows down a moving car or a falling parachute, and water resistance slows down a swimmer. It depends on the speed of the object, shape, and properties of the fluid.

5. State Newton’s First Law of Motion.

Answer:
Newton’s First Law of Motion states that a body continues in its state of rest or uniform motion in a straight line unless acted upon by some external force.

Explanation:
This law is also called the Law of Inertia. It means that objects resist any change in their motion. For example, a ball will not start rolling by itself and will not stop immediately unless forces like friction or a push act on it.