1. Regents Physics Mr. Rockensies
Friction
Regents Physics
Mr. Rockensies

2. These three factors make up the coefficient of friction
Friction – a force that opposes motion
Occurs whenever there is contact between two surfaces
Depends on 4 main factors:
The force the surfaces are applying to each other (Normal Force)
Materials the surfaces are made of
State of motion (static v. kinetic)
Presence of a lubricant (wet v. dry)
These three factors make up the coefficient of friction

3. Why does friction occur?
When objects are in contact with each other, down at the molecular level, even sooth surfaces have microscopic ridges.
Rough surface – more gaps ~ uneven
Smooth surface – more even, but still some gaps

4. A semi truck weighing 2400 N barrels down a highway at 40 m/s.
(a) What is the force of friction acting between the tires and the asphalt?
(b) How would it change if it were raining?
(c) If it were raining and the driver applied the brakes, how far would the truck travel before coming to rest?
(d) How long would it take to stop?

5. A wooden box is at rest on a wood floor. The box is 25 kg.
What is the weight of the box?
What is the Normal Force acting on the box?
What is the force of friction acting on the box?
What is the minimum force required to start the box moving?
(e) If the box is accelerated at a rate of 5 m/s2, what is the Net force acting on it?
(f) What is the Force of friction acting on the box?
(g) What is the force applied to actually move the box?

6. Exploring Friction
Using the spring scale and wooden block, determine the force of friction in each of the following scenarios:
Block flat on desk vs. block on its side
Pulling at a slow speed vs. pulling at a fast speed
Pulling across various surfaces
Pulling with a weight on top of the block
**Make sure to pull at a constant speed**

7. Record your values on a separate sheet of paper
For each scenario, determine whether or not the change affects friction
Block flat on desk vs. block on its side
Flat - ____ N
Side - ____ N
Pulling the block either way (does/does not) affect friction