Physics: Friction and Air Resistance Worksheet

Question 1

A student pushes a book across a desk. The book slows down and stops after the student lets go. Explain why the book stops.

Accepted Answer

The book stops because friction between the book and the desk acts in the direction opposite the book's motion. This friction force removes kinetic energy from the book and changes some of it into thermal energy.

Question 2

Which surface would usually create more friction for a sliding shoe: smooth ice or rough concrete? Explain your answer.

Accepted Answer

Rough concrete would usually create more friction because its surface has more bumps and irregularities that catch on the shoe. Smooth ice usually creates less friction, so objects slide more easily on it.

Question 3

A box is pushed to the right with a force of 25 newtons. Friction pushes to the left with a force of 10 newtons. What is the net force on the box, and in which direction does it act?

Accepted Answer

The net force is 15 newtons to the right. This is found by subtracting the 10 newtons of friction from the 25 newtons of applied force.

Question 4

A parachute helps a skydiver fall more slowly. Explain how air resistance changes when the parachute opens.

Accepted Answer

When the parachute opens, it spreads out and has a much larger surface area. This increases air resistance upward, which slows the skydiver's downward motion.

Question 5

Name two ways friction can be helpful in everyday life.

Accepted Answer

Friction is helpful because it allows shoes to grip the ground when we walk and allows brakes to slow down a bicycle or car. Without friction, it would be difficult to start, stop, or change direction.

Question 6

Name two ways friction can be a problem in machines.

Accepted Answer

Friction can be a problem because it can cause machine parts to wear down and it can change useful energy into unwanted thermal energy. This can make machines less efficient.

Question 7

A hockey puck slides farther on ice than a soccer ball rolls on grass. Use friction to explain why.

Accepted Answer

The hockey puck slides farther because ice has much less friction than grass. Grass creates more friction and rolling resistance, so the soccer ball slows down faster.

Question 8

Two identical toy cars roll down the same ramp. Car A has smooth wheels, and Car B has sticky rubber wheels. Which car will likely travel farther on a smooth floor after leaving the ramp? Explain why.

Accepted Answer

Car A will likely travel farther because its smooth wheels experience less friction with the floor. Car B's sticky rubber wheels create more friction, so it will slow down sooner.

Question 9

A falling leaf reaches terminal velocity. What does terminal velocity mean?

Accepted Answer

Terminal velocity means the leaf is falling at a constant speed because the upward air resistance force equals the downward force of gravity. The forces are balanced, so the leaf no longer speeds up.

Question 10

A cyclist bends low over the handlebars during a race. Explain how this position affects air resistance.

Accepted Answer

Bending low reduces the cyclist's front area facing the air. This decreases air resistance, so the cyclist can move faster with the same effort.

Question 11

A car travels at 20 meters per second. The engine provides a forward force of 1200 newtons, and air resistance plus road friction provide a backward force of 1200 newtons. Describe the car's motion.

Accepted Answer

The car moves at a constant speed because the forward and backward forces are equal. The net force is 0 newtons, so the car does not speed up or slow down.

Question 12

A student rubs their hands together quickly on a cold day. Why do their hands feel warmer?

Accepted Answer

Their hands feel warmer because friction changes some of the motion energy into thermal energy. This thermal energy increases the temperature of the skin on the hands.

Question 13

Look at a smooth ball and a crumpled paper ball of the same mass dropped from the same height. Which one is likely to fall faster through the air, and why?

Accepted Answer

The smooth ball is likely to fall faster because it usually has less air resistance than the crumpled paper ball. The crumpled paper has an irregular shape that catches more air and slows down more.

Question 14

A 40-newton crate is resting on the floor. A student pushes it with 8 newtons, but the crate does not move. What can you infer about the friction force?

Accepted Answer

The friction force must be 8 newtons in the opposite direction of the push. The crate does not move because static friction balances the student's push.

Question 15

Explain the difference between friction and air resistance.

Accepted Answer

Friction is a force that opposes motion when two surfaces touch. Air resistance is a type of fluid friction that opposes motion through air.

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Physics: Friction and Air Resistance

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