That Sticky Friction

Purpose: To understand how friction affects our world

Background

Friction is a force that opposes motion between the surfaces of two objects that are touching. Friction causes moving objects to slow down and eventually stop. It always acts in the direction opposite to the movement of an object. Friction is created when objects rub against each other. The surfaces of all objects, even objects that appear smooth, have microscopic bumps. When surfaces rub together, these bumps catch and rub each other, slowing the motion of the objects.

Materials

• shoe box
• large rubber band
• tape
• metric ruler
• flat surface
• marbles
• vegetable oil
• waxed paper
• craft stick
• science journal

Procedure

Teacher Prep:
Cut a small hole in one end of each shoebox.

1. Quickly rub your hands together hard for about one minute. Record your observations in your science journal.
2. Loop one end of the rubber band around the craft stick. See diagram 1.
3. Place the craft stick with the rubber band inside the shoe box.
4. Tightly pull the other end of the rubber band through the hole so that the craft stick is next to the side of the box. Tape the craft stick in place. See diagram 2.
5. Fill the box with marbles or small pebbles and replace the lid on the box.
6. Place the box on a flat surface.
7. Predict how far the rubber band will stretch before the box begins to move. Record your prediction in cm in your science journal.
8. Begin to pull the box and use the ruler to measure how long the rubber band stretches just before the box moves. Record.
9. Place a large piece of waxed paper on the flat surface and place the box on the waxed paper.
10. Repeat steps 7-8.
11. Pour enough vegetable oil to cover the surface of the waxed paper.
12. Repeat steps 7-8.

Conclusion

1. What did you feel when you rubbed your hands together? Why?
2. On which surface did the rubber band stretch the longest? Why?
3. Which surface required more force to start the box moving? Why?
4. The vegetable oil was used as a lubricant. How do lubricants help reduce friction?
5. What other lubricants are used every day?
6. How will friction affect the tree house detectives’ pulley system?

Extension

Try this experiment on various other surfaces such as sandpaper, concrete, vinyl, grass, and so on.