Q1.
the force of friction disappears in the world? How will the motion of objects be impacted?
Answer
Nothing that is moving would ever slow down on its own — and almost nothing could be started, steered or stopped by us.
- Moving objects would never stop. A ball rolled once, a cycle after you stop pedalling, a stack of coins released by a rubber band — each would keep moving with constant velocity for ever, exactly as Newton's first law predicts when the net force is zero.
- Walking and running would be impossible. You move forward because you push the ground backwards and friction pushes your foot forwards. With no friction your foot would just slide back and you would fall.
- Vehicles could neither accelerate nor brake. Tyres would spin without gripping; brakes work purely by friction.
- Nothing would stay where you put it. Knots, nails, screws, a glass on a slightly tilted table, a rope round a post — all rely on friction.
Why it happens: friction is the only horizontal contact force in most everyday situations. Remove it and the horizontal net force on a moving body becomes zero, so its velocity can never change by itself; and we lose the very force we use to push against the ground.
Tip: friction is often called a nuisance because it wastes energy, but this question shows it is also what makes controlled motion possible.