Friction Practice

Friction Calculations

By Mr. Gray

First, let's see what you know

Answer the following questions based on your observations of the Phet simulation and our classroom discussion so far.

Multiple Choice

If an object is moving at constant velocity, the applied force and the force of friction must be

• balanced

• unbalanced

Multiple Choice

If the force of friction acting on a moving object is greater than the applied force, the object will

• speed up

• slow down

• continue at constant velocity

Multiple Choice

If you are pushing on a heavy object but it isn't moving, you are unable to overcome

• static friction

• kinetic friction

Multiple Choice

Which object would likely have the highest coefficient of friction?

• ice

• floor tile

• concrete

• The would all be equal.

Now let's work on calculations.

Remember, you will get all the necessary equations on a quiz/test. For all calculations, use g = 10 m/s² for the acceleration of gravity. For open-ended questions, you ONLY need to enter the NUMBER part of your answer.

Multiple Choice

Amanda B. Reckenwyth is exerting a rightward force of 124.0 N in order to drag a 19.6-kg box of books across the floor at a constant speed of 0.26 m/s. Determine the force of gravity (F_grav). (W=m⋅g)

• 1.96 N

• 19.6 N

• 124 N

• 196 N

Multiple Choice

Amanda B. Reckenwyth is exerting a rightward force of 124.0 N in order to drag a 19.6-kg box of books across the floor at a constant speed of 0.26 m/s. Determine the normal force (F_norm).

• 1.96 N

• 19.6 N

• 124 N

• 196 N

Multiple Choice

Amanda B. Reckenwyth is exerting a rightward force of 124.0 N in order to drag a 19.6-kg box of books across the floor at a constant speed of 0.26 m/s. Determine the applied force (F_app).

• 1.96 N

• 19.6 N

• 124 N

• 196 N

Multiple Choice

Amanda B. Reckenwyth is exerting a rightward force of 124.0 N in order to drag a 19.6-kg box of books across the floor at a constant speed of 0.26 m/s. Determine the net force (F_net).

• 0 N

• 124 N

• 196 N

Multiple Choice

Amanda B. Reckenwyth is exerting a rightward force of 124.0 N in order to drag a 19.6-kg box of books across the floor at a constant speed of 0.26 m/s. Determine the force of friction (F_frict).

• 0 N

• 124 N

• 196 N

Multiple Choice

Amanda B. Reckenwyth is exerting a rightward force of 124.0 N in order to drag a 19.6-kg box of books across the floor at a constant speed of 0.26 m/s. Determine the coefficient of friction. (F_frict = μ⋅F_norm)

• 0

• 0.63

• 1

• 1.58

Open Ended

Consider the free-body diagram for an object accelerating across a surface. The object has a mass of 3.91-kg. There is a forward thrust force of 47.8 N. The coefficient of friction between the object and the surface is 0.567. Determine the weight (F_grav). (W=mg)

Open Ended

Consider the free-body diagram for an object accelerating across a surface. The object has a mass of 3.91-kg. There is a forward thrust force of 47.8 N. The coefficient of friction between the object and the surface is 0.567. Determine the normal force (F_norm).

Open Ended

Consider the free-body diagram for an object accelerating across a surface. The object has a mass of 3.91-kg. There is a forward thrust force of 47.8 N. The coefficient of friction between the object and the surface is 0.567. Determine the force of friction (F_frict). (F_f = μ⋅F_n)

Open Ended

Consider the free-body diagram for an object accelerating across a surface. The object has a mass of 3.91-kg. There is a forward thrust force of 47.8 N. The coefficient of friction between the object and the surface is 0.567. Determine the net force (F_net).

Open Ended

Consider the free-body diagram for an object accelerating across a surface. The object has a mass of 3.91-kg. There is a forward thrust force of 47.8 N. The coefficient of friction between the object and the surface is 0.567. Determine the acceleration. (F=ma)

Multiple Choice

True/False: The force of static friction can be greater than an applied force?

• True

• False

Multiple Choice

For the same object (and surface), the force of static friction will _ be greater than the force of kinetic friction

• never

• sometimes

• always

Multiple Choice

True/False: The coefficient of static friction for a surface is always greater than the coefficient of kinetic friction.

• True

• False

Open Ended

While decorating her apartment, Julie pushes a 64.7 kg dresser across the floor by applying a 557 N horizontal force. The coefficient of friction between the dresser and the floor is 0.54. Determine the acceleration of the dresser.

Equations: g = 10 m/s² W = m⋅g F_f = μ⋅F_n F_net = m⋅a

Apply what you learned

Determine the coefficients of friction

Set the friction slider to halfway between none and lots. Use any object to determine the coefficient of static friction and the coefficient of kinetic friction.

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