General Science Notes Chapter 7 Class 7 Maharashtra Board

Notes For All Chapters – General Science Class 7

Motion, Force and Work

1. Introduction

• Everything around us moves, like cars, birds, water, and even air.
• This movement is called motion, and it is caused by force.
• Work is done when a force moves an object.

2. Motion

What is Motion?

• Motion is when an object changes its position over time.
• Example: A moving car, a flying bird, or a running boy.

Types of Motion

Linear Motion – Movement in a straight line.

• Example: A car moving on a straight road.

Circular Motion – Movement in a circular path.

• Example: A fan’s blades spinning.

Periodic Motion – Motion that repeats after a fixed time.

• Example: A pendulum swinging, a clock’s hands.

3. Distance and Displacement

• Distance is always greater than or equal to displacement.

4. Speed and Velocity

What is Speed?

• Speed tells how fast an object is moving.

Formula:

• Speed=Distance traveled / Time taken​

Unit: Metres per second (m/s) or Kilometres per hour (km/h).

Types of Speed:

Uniform Speed – Moving at a constant speed.

• Example: A train moving at 60 km/h.

Non-uniform Speed – Speed keeps changing.

• Example: A car slowing down or speeding up in traffic.

What is Velocity?

• Velocity is speed with direction.
• Example: A car moving 50 km/h north.
• If direction changes, velocity also changes.

5. Acceleration

What is Acceleration?

• Acceleration is the change in velocity per second.

Formula: Acceleration=Change in velocity / Time taken

• Unit: Metres per second² (m/s²).

Types of Acceleration:

Positive Acceleration – Speed increases.

• Example: A bike speeding up.

Negative Acceleration (Deceleration) – Speed decreases.

• Example: A car slowing down at a red light.

6. Force

What is Force?

• Force is a push or pull that changes the motion of an object.
• Example: Kicking a football (push), pulling a door handle (pull).

Effects of Force:

1. Can start or stop motion (Kicking a ball starts motion, applying brakes stops it).
2. Can change speed (Pressing the accelerator makes a car go faster).
3. Can change direction (Hitting a cricket ball with a bat).
4. Can change shape (Pressing a sponge).

Types of Force:

Contact Force – Needs physical contact.

• Example: Pushing a box, friction.

Non-contact Force – Acts from a distance.

• Example: Magnetic force, gravity.

7. Newton’s Laws of Motion

Newton’s First Law (Law of Inertia)

• An object at rest stays at rest, and an object in motion stays in motion unless a force is applied.
• Example: A book stays on a table unless someone moves it.

Newton’s Second Law (Force and Acceleration)

• Force = Mass × Acceleration (F = ma).
• A heavier object needs more force to move.

Newton’s Third Law (Action-Reaction)

• “For every action, there is an equal and opposite reaction.”
• Example: When we jump, we push the ground downward, and the ground pushes us upward.

8. Work

What is Work?

• Work is done when a force moves an object in the same direction as the force.

Formula: Work=Force × Displacement

• Unit: Joule (J).

When is Work Done?

1. Work is done → Pushing a box and moving it.
2. Work is not done → Pushing a wall (if it doesn’t move).

9. Energy

What is Energy?

• Energy is the capacity to do work.
• Unit: Joule (J).

Types of Energy:

Kinetic Energy – Energy of a moving object.

• Example: A moving car, flowing water.

Potential Energy – Stored energy.

• Example: Water stored in a dam, stretched rubber band.

10. Simple Machines and Work

Simple machines help us do work easily by reducing effort.

Examples of simple machines:

• Lever – A seesaw, crowbar.
• Pulley – Lifting buckets from a well.
• Inclined Plane – A ramp for moving heavy objects.

11. Difference Between Distance and Displacement

12. Importance of Motion, Force, and Work

• Motion helps in transportation and daily activities.
• Force is needed to move or stop objects.
• Work is done whenever force moves something.
• Energy is needed to perform any activity.