Name: Block: Date:
Friction
A crate filled with delicious junk food rests on a horizontal floor. The crate’s mass is 50kg. A hungry stick figure stands by, ready to haul the crate away to its lair.
1. The crate is sitting on the floor. Only gravity and the normal force of the floor act on the crate.a. Draw and label the forces acting on the crate.
b. The net force on the crate is: (zero) (greater than zero)
c. Evidence for this is ______
2. The stick figure exerts a slight pull FT on the crate, not enough to move it. A force of friction now acts.
a. Add the two forces to the diagram: the FT and Ff .
b. The friction force is:
(less than) (equal to) (greater than) FT.
c. The net force on the crate is: (zero) (greater than zero)
3. The stick figure increases the pull FT until the crate begins to move with constant velocity across the floor.
a. Add FT and Ff to the diagram.
b. The friction force is (less than) (equal to) (greater than) FT.
c. Constant velocity means acceleration is
(zero) (greater than zero)
d. The net force on the crate is
(less than) (equal to) (greater than) zero
4. The stick figure pulls harder and now the pull FT is greater than the friction FF.
a. Add FT and Ff to the diagram.
b. The net force on the crate is now
(less than) (equal to) (greater than) zero
c. The net force acts to the right, so acceleration acts toward the
(left) (right)
5. If the pulling force FT is 150 N and the crate doesn’t move, what is the magnitude of FF? _____
6. If the pulling force FT is 200 N and the crate doesn’t move, what is the magnitude of FF? _____
The friction in this case is called (static) (kinetic) friction.
7. If the force of sliding friction is 250 N, what force is necessary to keep the crate sliding at constant velocity? _____ The friction in this case is called (static) (kinetic) friction.
8. Recall that the mass of the crate is 50 kg. If this sliding friction is 250 N, what is the acceleration of the crate when the pulling force is 250 N? _____ 300 N? _____ 500 N? _____