# elastic force

## using elastic force

Elastic force can be very useful and not just for bungee jumping. In fact, you probably use elastic force every day. A few common uses of elastic force are shown in the Figure 1.1. Do you use elastic force in any of these ways? Q: How does the resistance band work? How does it use elastic force? A: When you pull on the band, it stretches but doesnt break. The resistance you feel when you pull on it is elastic force. The farther you stretch the band, the greater the resistance is. The resistance of the band to stretching is what gives your muscles a workout. After you stop pulling on the band, it returns to its original shape, ready for the next stretch. Springs like the spring toy pictured in the Figure 1.2 also have elastic force when they are stretched or compressed. Q: Can you think of other uses of springs? A: Bedsprings provide springy support beneath a mattress. The spring in a door closer pulls the door shut. The spring in a retractable ballpoint pen retracts the point of the pen. The spring in a pogo stick bounces the rider up off the ground.

## elasticity and elastic force

Something that is elastic can return to its original shape after being stretched or compressed. This property is called elasticity. As you stretch or compress an elastic material like a bungee cord, it resists the change in shape. It exerts a counter force in the opposite direction. This force is called elastic force. The farther the material is stretched or compressed, the greater the elastic force becomes. As soon as the stretching or compressing force is released, elastic force causes the material to spring back to its original shape. Click image to the left or use the URL below. URL: Q: What force stretches the bungee cord after the jumper jumps? When does the bungee cord snap back to its original shape? A: After the bungee jumper jumps, he accelerates toward the ground due to gravity. His weight stretches the bungee cord. As the bungee cord stretches, it exerts elastic force upward against the jumper, which slows his descent and brings him to a momentary stop. Then the bungee cord springs back to its original shape, and the jumper bounces upward.

## instructional diagrams

No diagram descriptions associated with this lesson

## questions

the less an elastic material is stretched or compressed, the greater the force it exerts.

``````a. true

-->  b. false
``````

elastic force causes an elastic material to spring back to its original shape after being stretched or compressed.

``````-->  a. true

b. false
``````

play objects with elasticity include

``````-->  a) spring toys.

b) silly putty.

c) modeling clay.

d) all of the above
``````

an elastic material offers no resistance to forces that change its shape.

``````a. true

-->  b. false
``````

## diagram questions

No diagram questions associated with this lesson