# Material Friction

### Research Questions:

• What materials cause friction?

Friction is the resisting force between two objects sliding against each other. When we rub our hands together on a cold day it is friction that produces the heat. What happens when you try to walk on ice? You can walk slower to maintain balance or slip. This occurs because there is little friction between the sole of your shoe and the ice. Friction is a necessary force in our world. Without it we would not be able to walk or hold objects in our hands. In this experiment we will examine the nature of friction and how various materials affect movement.

### Materials:

• 2" x 4" x 4" block of wood
• 1" x 8" x 36" wood board
• Ruler or yard stick
• Stop watch
• Various types of material to test: wood, aluminum foil, cotton cloth, rubber, oil, etc.

### Experimental Procedure:

1. Create a ramp. Sand the wood block and board so that the surfaces are smooth and will not cause splinters. Using a ruler or a yard stick measure 8" from each end of the board. Prop one end of the board up on a stack of books.
2. Place the block of wood at the top of the ramp. Release the block of wood, do not push it. The wood should slide down the board. If it does not slide increase the incline of the ramp by stacking more books.
3. Using a stop watch record the time it takes for the block of wood to slide from the top mark to the bottom mark. As soon as the front end of the block crosses the top mark start your timer. Once the back end of the block crosses the end mark stop your timer. Repeat 2 more times.

1. Record your times on a chart and calculate the average time between the 3 trials.
2. Cover the surface of the board with aluminum foil. Use tape to secure the foil. Repeat steps 3 & 4.
3. Cover the surface of the board with a piece of cotton cloth. Repeat steps 3 & 4.
4. Coat the surface of the board with a this layer of oil (cooking oil, mineral oil). Repeat steps 3 & 4.
5. Choose 3 more materials to test on the surface of the board. Use your background research for ideas on what kinds of materials to test. Repeat steps 3 & 4.
6. From your chart compare the average times for each surface. Which had the fastest time? Which had the slowest time?
7. Calculate speed for each trial using the average time: length (inches) from start to end mark / average time.

Speed = Distance / Time

1. How did friction affect the speed of the block sliding down the incline?
2. Discuss how the properties of the materials tested contribute to frictional force.

 Trial 1 Trial 2 Trial 3 Wood 5.02s 4.98s 5.22s Aluminum 4.22s 4.1s 4.33s Mineral Oil 3.11s 3.32s 3.02s Cotton Cloth 7.22s 7.53s 7.34s

Terms:  Friction; Types of friction; Force; Gravity; Resistance

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