What Do Wedges Do?

A wedge is a simple machine that is actually part of a subset of inclined planes. What makes the wedge special is how it is used. Inclined planes make it easier to raise things, but when an inclined plane is used as a wedge, what does it do?

 

Materials

Large box full of uncooked rice

Rectangular block

Triangular block

Pictures of examples of wedges (Bow of a boat, ax splitting wood, knife cutting through cheese or butter, etc.)

 

What To Do

Place the box of rice on the table and smooth the surface of the rice so it is evenly distributed. Place the rectangular block in the rice at one end of the box. Make sure the block is submerged/embedded in the rice. Push the block to the other end of the box, paying close attention to the amount of effort used. Also notice what happens to the rice as the block is pushed through it. Remove the rectangular block from the rice and again smooth the rice so it is evenly distributed. Place the triangular block in the rice at one end of the box with the base of the triangle toward the wall and the point of the triangle facing the opposite end of the box. Make sure the block is submerged/embedded in the rice. Push the block to the other end of the box, paying close attention to the amount of effort used. Also observe what happens to the rice as the block is pushed through it. Did you notice any differences? 

 

Questions

1. Was it easier to move the rectangular block or the triangular block through the rice? (Triangular)

2. What happened to the rice as the triangular block was pushed through it? Where did it go? (It was pushed to the sides)

3. What do wedges do? (Spread things apart)

 

Summary

Wedges are inclined planes that split things apart. When woodcutters split wood they pound a wedge into the log to force it apart. Knives are also wedges, and so are the bows of boats and ships, cutting through water to make it easier for the ship to move forward. This activity was designed to help students understand that wedges are used to push things apart, and to reduce the force needed to do so.

 

Source

"Bathtubs, Slides, and Roller Coaster Rails: Simple Machines That Are Really Inclined Planes." Christopher Lampton. Millbrook Press, Brookfield: 1991. ISBN: 1-878841-23-8.

© S. Olesik, WOW Project, Ohio State University, 2003.