Friction

What type of friction is not moving?

• static
• sliding
• fluid
• rolling

Which of the following is an example of friction that is helpful?

• Brakes used on a bike
• Tires from a car on the road
• Tread on the bottom of your shoes
• All are examples that are helpful

How would the absence of friction affect a marble traveling on a long, straight path?

• The marble’s speed would decrease.
• The marble’s speed would increase.
• The marble would stop immediately. 
• The marble would remain at constant speed.

F_N=100N, F_f=20N

• μ=5.0

• μ=0.2

• μ=1.2

• μ=0.1

What direction does friction act relative to motion?

• in the same direction
• in the opposite direction 
• need more information
• depends on the force

What is the coefficient of static friction if it takes 44 N of force to move a box that weighs 86 N? 

• 0.78
• 0.51
• 0.78 N
• 0.58 N

A box takes 40 N to start moving when the coefficient of static friction is .54. What is the weight of the box? 

• 81 N
• 18 N
• 98 N
• 74 N

When looking at friction problems, if the net force in the x-direction on an object is zero, what can we say about its acceleration?

• it is positive

• it is negative

• it is zero

• not enough information is given

Normal force is

• Always opposite the weight

• Always parallel and down the incline

• Always perpendicular to the surface

• It depends on the direction of motion

 What is the force of friction between a block of ice that weighs 950 N and the ground if μ = .12? Ff = Fn*μ

• 65 N

• 226 N

• 175 N

• 114 N