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You stop pedalling and the cycle slowly comes to rest. What made it stop?

This is Chapter 6 of your Class 9 book, Exploration. It is called How Forces Affect Motion. The last chapter described motion. This one asks what changes it.

What you will learn

• No force, no change — Newton's first law.
• Inertia and mass — why heavy things resist change.
• Force and acceleration — F = ma, force = mass × acceleration.
• Friction with numbers — a force in the same calculation.
• Action and reaction — Newton's third law.
• Equal forces, unequal motion — why pairs never cancel.
• Softening a stop — why a longer stop needs less force.
• Which law answers — pick the law for the question.
• Force from a graph — the slope gives acceleration.
• Two boxes, one system — a string joins them.

Need a quick recap?

You met these ideas in earlier classes.

• A force — a push or a pull, with a direction.
• Friction — a force that acts against motion.
• Acceleration — how fast the velocity changes.

Start with the cycle. Why does it stop?