friction

CP Physics Lab Friction- It's a Drag, Man! Discussion:
All surfaces exhibit some type of frictional force that resists motion. This frictional force depends only on the two surfaces that are in contact and the weight of the object trying to move. There are two types of friction, static and kinetic. Static friction must be overcome to start an object moving and kinetic ocurrs after an object as begun moving.

Purpose: The purpose of this lab is to determine the coefficient of friction for static and kinetic friction for different surfaces and compare which one is stronger.

Materials: Force sensor and computer, 3 1 kg masses, board, 2 shoes (preferably different types like tennis shoe and flip flop), wood with hook and different surfaces

Procedure:

Computer set up:

1) Plug in sensor

2) Launch Data Studio

3) Click on "Summary" window tab

4) Click on "set up" window tab. Make sure the force sensor set up is "Force pull positive" then close window.

5) Drag the "digits" icon into the force sensor (a window with blanks should appear)

6) Hang a mass on your force sensor and check if it is working when you click start. What should it read according to the mass you are hanging? Does it?

Measuring kinetic frictional force:

1) Determine the weight of the block.

2) Drag the block with one of its surfaces along the board using the force sensor. Make sure the force sensor stays parallel to the surface. Drag the block at a CONSTANT velocity so that the force remains constant.

3) Record the force of gravity on the block, normal force, applied force, and frictional force. (Some of these are the same, but record them still).

4) Repeat for 3 trials total.

5) Repeat but add one mass, then two masses, then three masses. (That is 12 trials!!)

6) Repeat for all surfaces of the block.

7) Repeat with two different shoes.

Measuring static frictional force:

1) Place a side of the block on the wooden board.

2) Lift the board until the block just starts to slide.

3) Measure the angle where the shoe starts to slide.

4) Calculate the coefficient of static friction using the equation "mu" = tan(angle)

5) Record the angle and mu.

6) Repeat for each surface and each shoe.

Data:

Kinetic friction:

Surface =	Trial	Fg (N)	Fa (N)	Fn (N)	Ff (N)	Surface =	Trial	Fg (N)	Fa (N)	Fn (N)	Ff (N)
.	1	.	.	.	.	.	1	.	.	.	.
.	2	.	.	.	.	.	2	.	.	.	.
.	3	.	.	.	.	.	3	.	.	.	.
.	avg	.	.	.	.	.	avg	.	.	.	.
.	1	.	.	.	.	.	1	.	.	.	.
.	2	.	.	.	.	.	2	.	.	.	.
.	3	.	.	.	.	.	3	.	.	.	.
.	avg	.	.	.	.	.	avg	.	.	.	.
.	1	.	.	.	.	.	1	.	.	.	.
.	2	.	.	.	.	.	2	.	.	.	.
.	3	.	.	.	.	.	3	.	.	.	.
.	avg	.	.	.	.	.	avg	.	.	.	.
.	1	.	.	.	.	.	1	.	.	.	.
.	2	.	.	.	.	.	2	.	.	.	.
.	3	.	.	.	.	.	3	.	.	.	.
.	avg	.	.	.	.	.	avg	.	.	.	.

Shoe 1 =	Trial	Fg (N)	Fa (N)	Fn (N)	Ff (N)	Shoe 2 =	Trial	Fg (N)	Fa (N)	Fn (N)	Ff (N)
.	1	.	.	.	.	.	1	.	.	.	.
.	2	.	.	.	.	.	2	.	.	.	.
.	3	.	.	.	.	.	3	.	.	.	.
.	avg	.	.	.	.	.	avg	.	.	.	.
.	1	.	.	.	.	.	1	.	.	.	.
.	2	.	.	.	.	.	2	.	.	.	.
.	3	.	.	.	.	.	3	.	.	.	.
.	avg	.	.	.	.	.	avg	.	.	.	.
.	1	.	.	.	.	.	1	.	.	.	.
.	2	.	.	.	.	.	2	.	.	.	.
.	3	.	.	.	.	.	3	.	.	.	.
.	avg	.	.	.	.	.	avg	.	.	.	.
.	1	.	.	.	.	.	1	.	.	.	.
.	2	.	.	.	.	.	2	.	.	.	.
.	3	.	.	.	.	.	3	.	.	.	.
.	avg	.	.	.	.	.	avg	.	.	.	.

Static Friction: (Show 5 step calcuation next to table)

Surface	angle	mu
.	.	.
.	.	.
.	.	.
.	.	.

Graphing:

1) Make a graph using EXCEL for each block surface of Fn vs Ff. (Fn is on x-axis, and Ff is on y-axis)

Use x-y scatter plot, no line connecting
Add a new series for each surface so there are FOUR lines on the graph
Add a trend line to each graph (what type should it be??)
Make sure to click on equation, y-intercept = 0, and R value for trend line

2) Make a graph using EXCEL for each shoe. Do the same as above but this time there are only TWO lines.

ANALYSIS:

QUESTION 1: What is the slope for each surface and shoe? What does the slope represent?

QUESTION 2: According to your graphs, what is the equation that relates Ff and Fn? Use the appropriate symbol for your slope.

QUESTION 3: What is the coefficient of kinetic friction for each surface and shoe?

QUESTION 4: How does the coeffictient of kinetic fricton compare to the coefficient of static friction?

QUESTION 4: What would you use a high coefficient of friction shoe for? What would you use a low coefficient of friction shoe for?

STANDARD LAB REPORT REQUIRED!