1. 2. What happens if the force is increased?
Do Now:
1. A copper block of mass 10 kg is being dragged horizontally across a steel table at a constant speed. What force is pulling the block?
2. What happens if the force is increased?

2. Practice
A 10 kg box is pulled by a rope with 80 N force. The coefficient of kinetic friction is 0.2. Does the box move and which way? Draw FBD! What is the boxes acceleration? FF
Fp = 80N
m = 10 kg

3. Envelope Activity
Use the information in your envelope to solve the question together as a group. Make sure to take any notes you might think are important.

4. Lauren is driving a car on an icy road with a constant velocity of 20 m/s. Her and the car have a combined mass of 1,500 kg. (Use rubber on ice for μ)
What is the coefficient of friction?
Draw a FBD for when the breaks are applied.
What is the Force of friction when she hits the breaks hard to skid to a stop?
How long does it take her to stop?

5. Example
1. Connor is trying pull wood across his wood floor to put into the fireplace. He pulls at a 30o angle with a force of 100 N. If the wood has a mass of 20 kg, will he be able to move it?

6. Individual Exercise
Mike is dragging a sack of potatoes with a weight of 600N across the floor. The coefficient of static friction is .25 for the bag on the floor. If he pulls at 60o with a force of 200N, will the bag move?

7. Example 4 (advanced):
What is the coefficient of friction of a tire on a level road if a car decelerates at a rate of 3 m/s2 once the driver takes her foot off the gas pedal?
a = Fnet / m = Ff / m = µFN / m = µmg/m = µg
3 m/s2 = µ (9.8 m/s2)
µ = 3 m/s2 / 9.8 m/s2
µ = .31

8. Review
A crate is pulled with a NET force on a rough surface. Draw a FBD.
If the Crate were filled, what would happen to the coefficient of friction? (Kinetic or static)
If the crate were filled, what would happen to the Force of friction?