No Static Vs Kinetic

No static vs kinetic!!!!!!!!! Name (First AND Last): ______Date: ______Friction Lab (614) Modified from “The Force of Friction Acting on a Wooden Block” in Methods of Motion. Background: The force of friction is one of the “hidden” forces that affect the motion of objects on Earth. Forces like these are hidden in the sense that they are so common that we sometimes take them for granted and overlook them. The force of friction and other “hidden” forces must be recognized if we are to describe and predict motion accurately.

Objectives:  To measure the friction force acting on a piece of wood.  To explore a few of the variables which affect the size of the force of friction.

Procedure for Part A: For this section of the lab, each lab group will be assigned to a particular lab station. At each station you will find a wood block, a “surface”, a spring scale, and a few masses. Each lab group will test a different surface. When everyone is done collecting data, the class will share their results. 1. Adjust the spring scale so that when held vertically it reads zero. 2. Note what type of spring scale is at this station. If it is a 5N spring scale, each small line represents .2N. If it is a 20N spring scale, each small line represents .5N. 3. Record the type of spring scale and the name of the “surface” in the data table on the next page. 4. Attach the hook of the spring scale to the hook on the wood block as shown in the diagram. Place the wood block on the “surface.”

Spring Scale Block 5. Gently pull on the scale so that the block moves in a straight line and at a constant speed. Read the scale while the block is moving. 6. Record your reading in the data table that is below. This is the number of Newtons of force required to keep the block moving at a constant speed. “Surface” Spring Scale Trial #1 Trial #2 Trial #3 (5N or 20N)

7. Repeat the experiment until you have a total of three pieces of data. 8. Share your data with the class and record your classmates’ data in the table below.

Data for Part A (10 points total) Don’t forget units on ALL measurements!

“Surface” Spring Scale Trial #1 Trial #2 Trial #3 Average (5N or 20N)

Calculations for Part A (2 points) Use your calculator to calculate the average force for each “surface.” Remember that this is the average force required to keep the block moving at a constant velocity. Fill in the averages above. Don’t forget units! Questions for Part A: Answer in complete sentences! (2 points each) 1. Which “surface” required the most applied force? How would you describe the surface to someone who has never touched it? How does it feel?

2. Which “surface” required the least applied force? How would you describe the surface to someone who has never touched it? How does it feel?

3. Draw a free-body diagram of the box when it is being pulled at a slow, constant speed.

4. The box is moving at constant speed. It is in equilibrium. What does this mean about the size of your arrows? How does the size of the applied force compare with the size of the friction force? Procedure for Part B: In Part B of this lab, you will explore a few of the variables that may (or may not!) affect the size of the force of friction. You will use the same surface that you used in Part A. 1. Find your original data for your surface. Copy this data into row 1 of the data table on the next page. 2. Add 200g of mass to the block. Repeat your previous procedure (dragging and measuring) three times. Record your data into row 2 of the data table on the next page. 3. Add mass until a total of 500g of mass is on top of the block. Repeat your previous procedure (dragging and measuring) three times. Record your data into row 3 of the data table on the next page. 4. If you have a rough surface, remove the extra mass. If you have smooth surface, you can keep the extra mass. (If you use extra mass, it is very important to record that in the data table.) Now take a closer look at how much force it takes to get the block moving. Repeat your previous procedure (dragging and measuring) three times. This time you are looking for the data at the moment JUST BEFORE the block starts to move. If you are having trouble getting good readings, try adjusting the amount of mass on your block. Record your data into row 4 of the data table on the next page. 5. Rotate the block so that it is resting on its narrow side. Let’s see if surface area makes a difference. Repeat your previous procedure (dragging and measuring) three times. Record your data into row 5 of the data table on the next page. 6. Put the block back down on its largest side. Try pulling the block at a different constant speed. Repeat your previous procedure (dragging and measuring) three times. Record your data into row 6 of the data table on the next page. Data for Part B (12 points) Don’t forget units on all measurements!

“Surface” Spring Variable Additional Trial Trial Trial Average Scale Mass? If #1 #2 #3 (5N or yes, how 20N) much? Original No 1 Data +200g Yes, +200g 2 +500g Yes, +500g 3 Starting 4 Surface 5 Area Speed 6

Calculations for Part B (2 points) Use your calculator to calculate the average force for each variable. Remember that this is the average force required to keep the block moving at a constant velocity. Fill in the averages above. Don’t forget units!

Questions for Part B: Answer in complete sentences! (2 points each) 1. How did adding mass to your block change the amount of force necessary? What is the relationship between necessary applied force and mass of block? 2. What did you observe when you observed the block while it was starting? Were the measured forces different from or the same as the measured forces during motion? When is the applied force larger (at the start or during motion)?

3. How did changing the surface area affect the friction? Do you think surface area is an important factor when considering friction forces?

4. Did you find that speed affects the frictional force acting on the block? If you did see an effect, how were they related?

5. We are almost talking about the applied force necessary and the frictional force acting as if they are the same thing. Are they? Why are we speaking about them as if they are the same? Is this always true? Extensions for Extra Credit 1. What are some of the things that are done in the real world to reduce the effects of friction? Explain each.

2. Is friction ever helpful rather than hurtful? Provide examples and explain.

3. Place a few pens or pencil between your block and your surface. Now pull the block with spring scale. How much force must you exert? Is it more or less than without the “rollers”? Are you surprised? Explain.