CBSE Class 9 Science Notes Chapter 1 Motion (PW) NOTES

 PHYSICS

CBSE Class 9 Science Notes Chapter 1 Motion

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📘 Chapter: Motion (Class 9 Science)

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✅ 1. Introduction to Motion

• Motion: A body is said to be in motion if it changes its position with time relative to a reference point.

• Types of motion:

  • Translational (linear)

  • Rotational

  • Oscillatory

  • Random

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✅ 2. Types of Motion

• Uniform Motion: Equal distances in equal intervals of time.

• Non-uniform Motion: Unequal distances in equal intervals of time.

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✅ 3. Basic Terms

Term	Definition	SI Unit
Distance	Total path covered	meter (m)
Displacement	Shortest path from initial to final point	meter (m)
Speed	Distance/time	m/s
Velocity	Displacement/time	m/s
Acceleration	Rate of change of velocity	m/s²

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✅ 4. Equations of Motion (only for uniform acceleration)

Let:

• u = initial velocity

• v = final velocity

• a = acceleration

• s = displacement

• t = time

Three equations:

1. $v = u + at$

2. $s = ut + \frac{1}{2}at^2$

3. $v^2 = u^2 + 2as$

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✅ 5. Graphical Representation

• Distance-Time Graph:

  • Uniform motion → straight line

  • Non-uniform motion → curved line

• Velocity-Time Graph:

  • Uniform acceleration → straight sloped line

  • Area under curve = displacement

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✅ 6. Uniform Circular Motion

• Definition: When a body moves in a circular path with constant speed.

• Velocity changes due to changing direction.

• Centripetal Force acts towards the center.

• Example: Moon around Earth.

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📝 Important Notes

• Displacement can be zero even when distance is not (e.g., going around a circle and coming back to the start).

• Acceleration is positive for speeding up and negative (retardation) for slowing down.