September 14September 14

AP physicsAP physics

IN: Unbeknownst to the students, every IN: Unbeknownst to the students, every time the school floors are waxed, time the school floors are waxed, Mr. Tobin likes to slide down the Mr. Tobin likes to slide down the hallway in his socks. Mr. Tobin hallway in his socks. Mr. Tobin weighs 850 N and the coefficient of weighs 850 N and the coefficient of kinetic friction between his socks kinetic friction between his socks and the floor is 0.120. What is the and the floor is 0.120. What is the force of friction that opposes Mr. force of friction that opposes Mr. Tobin’s motion down the hall?Tobin’s motion down the hall?

Objective:Objective:

Understand the force of friction.Understand the force of friction.

Success criteria:Success criteria:

Add friction to Newton's law Add friction to Newton's law problems.problems.

Homework checkHomework check

A 700 kg polar bear A 700 kg polar bear slides across the slides across the ice with a force of ice with a force of friction of 25 N. friction of 25 N.

What is the What is the coefficient of coefficient of friction between friction between fur and ice?fur and ice?

A 150 kg skiier slides A 150 kg skiier slides down a 20down a 20oo slope. The slope. The coefficient of kinetic coefficient of kinetic friction between skiis friction between skiis and snow is .1. and snow is .1.

What is the normal What is the normal force? force?

What is the force What is the force down the hill? down the hill?

What is the net force What is the net force down the hill?down the hill?

What is his What is his acceleration down the acceleration down the hill?hill?

A 25 kg boy slides A 25 kg boy slides along a slip-n-slide. along a slip-n-slide. He slows down He slows down with an with an acceleration of .5 acceleration of .5

m/sm/s22. What is . What is µµkk between the slide between the slide and the boy?and the boy?

A group of people pull a 200,000 kg A group of people pull a 200,000 kg plane with a force of 40,000 N to keep plane with a force of 40,000 N to keep it moving at a constant velocity. it moving at a constant velocity.

What is the kinetic force of friction?What is the kinetic force of friction? What is the coefficient of kinetic What is the coefficient of kinetic

friction of the tires on the tarmack?friction of the tires on the tarmack?

A 20 N block is being pushed across a A 20 N block is being pushed across a horizontal table by an 18 N force. If horizontal table by an 18 N force. If the coefficient of kinetic friction the coefficient of kinetic friction between the block and the table is between the block and the table is 0.4, find the acceleration of the block.0.4, find the acceleration of the block.

a) 0.5 m/s2a) 0.5 m/s2

b) 1 m/s2b) 1 m/s2

c) 5 m/s2c) 5 m/s2

d) 7.5 m/s2d) 7.5 m/s2

e) 9 m/s2e) 9 m/s2

Out:Out: