Ms. Barlow’s 8th Grade Physical Science Class

A force is a push or a pull. Friction is a rubbing force that acts against motion between two touching surfaces and always slows an object down.

Question: How does the force that is needed to overcome friction change for different surfaces?

Materials: wooden block, whiteboard, one or two books, various surface materials, spring scale

Test the Hypothesis/Collect DataDescribe the texture of each surface before

running the tests for friction. Then, hypothesize which surface will have the most friction and require more force to overcome.

 

1. Make a short ramp out of a white board and one or more books on a table.

2. Hook the spring scale under the block. Place the block at the bottom of the ramp.

3. Pull the block up the ramp and record the amount of force needed to pull the block up in Newtons (N).

4. Change the surface of the table by covering it with plastic wrap. Repeat step 3. Change the surface two more times using cardboard, and carpeting. Repeat step 3 again.

Parts of the experiment: Independent Variable: (what are you

changing)  Dependent Variable: (what are you

measuring)  Constants: (what remains the same)

Surface Description of Texture

Force (N)needed to move object up

the ramp

white board

plastic wrap

cardboardcarpet

Mass of the block________________________

1. Which surface had the most friction? The least? How can you tell?

2. What do you predict about the amount of force needed to move the object and overcome friction if the mass is increased?

3. If the object is not moving, the forces are balanced. What happens to the forces when you pull the block up the ramp?

4. What affect does the amount of friction have on the motion of the block going down the ramp? (put the block on top of the ramp and let it go)

5. Suppose you and your little brother are swimming at a neighborhood pool. Your little brother asks, “Why there are signs everywhere that say NO RUNNING?” How would you respond and at the same time, teach him about friction?

 Conclusion: 6. Describe the effect of friction on balanced

and unbalanced forces.

Real World Application:5. When designing a race car, what do the

engineers need to think about in terms of friction?