Friction Quiz

Laws of Dry Friction Coefficients of Static vs. Kinetic

Friction Impending Motion, Angle of Friction

1. Which statement best defines dry friction?

a) The force parallel to the surface of two objects in contact with each other.b) The normal force of two objects in contact with each other.c) The perpendicular force of two objects in contact with each other.d) The force that resists an object rolling across a surface.

2. What horizontal force starts the object moving, if it weighs 50.0 kg and static=0.60?

a) 50.0 Nb) 83.3 Nc) 294 Nd) 491 N

Fapplied

W = weight

Fnormal

Ffriction

3. What is the normal force in the following figure if W=200 N and Fapplied=100 N?

a) 100.0 Nb) 106.0 Nc) 165.8 Nd) 200 N

Fapplied

W

Fnormal

Ffriction

+

n

t

4. What is the maximum frictional force in the figure below if W=200 N, Fapplied=100 N and static=0.60?

a) 99.5 Nb) 106.8 Nc) 165.8 Nd) 200 N

Fapplied

W

Fnormal

Ffriction

+

n

t

5. What is coefficient of kinetic friction in the figure below if Fhorizontal=200 N, Fvertical=650 N, W=800 N and the object is moving?

a) 0.200b) 0.308c) 0.600d) 0.250

Fapplied

W = weight

Fvertical

Fhorizontal

6. Compute the coefficient of static friction from the following figure assuming slippage is about to occur.

a) 0.902b) 0.477c) 0.445d) 0.431

25.5 deg

W = 50.0 N

Correct answers

1) a (tangential or parallel force)

2) c (=50.0 x 9.81 x 0.60)3) c (=200 – 100 sin20°)4) a (=165.8 x 0.60)5) b (=Fh/Fv = 200/650)

6) b (=tan 25.5°)

Rank yourself

5-6: Consider tribology (friction science) as a career.

3-4: Check that your calculator is using the metric system.

0-2: You are on a slippery slope, increase your normal forces and study habits.