What is friction?

• A force that promotes motion
• A force that opposes motion
• A force that has no effect on motion
• A force that only acts in one direction

Which type of friction must be overcome to start moving an object?

• Kinetic friction
• Static friction
• Dynamic friction
• Rolling friction

Which of the following statements about static friction is true?

• It is always less than kinetic friction
• It acts when objects are moving
• It acts when objects are stationary
• It has no formula

What is the formula for static friction?

• Fs = μk × N
• Fs = μs × N
• Fs = N × g
• Fs = μs + N

Which of the following factors increases friction?

• Smoother surfaces
• Lower normal force
• Higher normal force
• Higher speed

If a box has a mass of 50 kg and is on a surface with a coefficient of kinetic friction (μk) of 0.2, what is the normal force acting on the box?

• 490 N
• 50 N
• 98 N
• 0 N

What is the kinetic friction force acting on the box in the previous question?

• 98 N
• 490 N
• 10 N
• 0 N

Why do trains need clean wheels?

• To reduce weight
• To increase speed
• To ensure proper friction with tracks
• To improve aesthetics

Which of the following is an example of low friction?

• Walking on concrete
• Sliding on ice
• Writing with a pencil
• Using sandpaper

What is the coefficient of static friction for steel on steel (dry)?

• 0.03
• 0.74
• 0.5
• 1.0