# elastic force

## 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, it resists the change in shape. It exerts a counter force in the opposite direction. This force is called elastic force. Elastic force causes the material to spring back to its original shape as soon as the stretching or compressing force is released. You can watch a demonstration of elastic force at this URL: (3:57). MEDIA Click image to the left or use the URL below. URL:

## using elastic force

Elastic force can be very useful. You probably use it yourself every day. A few common uses of elastic force are pictured in Figure 13.25. Did you ever use a resistance band like the one in the figure? When you pull on the band, it stretches but doesnt break. The resistance you feel when you pull on it is elastic force. 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 workout. Springs like the ones in Figure 13.26 also have elastic force when they are stretched or compressed. And like stretchy materials, they return to their original shape when the stretching or compressing force is released. Because of these properties, springs are used in scales to measure weight. They also cushion the ride in a car and provide springy support beneath a mattress. Can you think of other uses of springs?

## instructional diagrams

No diagram descriptions associated with this lesson

## questions

Which of the following items has the property of elasticity?

``````-->  a. rubber band

b. paper clip

c. toothpick

d. iron nail
``````

force exerted on a material that is pulled apart

``````a. elastic force

-->  b. stretching force

c. compressing force

d. elasticity

e. spring
``````

structure that returns to its original shape after being stretched or compressed

``````a. elastic force

b. stretching force

c. compressing force

d. elasticity

-->  e. spring
``````

When does an elastic material exert elastic force?

``````a. before it is stretched

b. as it is stretched

c. when it is released

-->  d. two of the above
``````

force exerted on a material that is pushed together

``````a. elastic force

b. stretching force

-->  c. compressing force

d. elasticity

e. spring
``````

What happens when you pull on a bungee cord?

``````a. It stretches.

b. It resists the change in shape.

c. It exerts force in the opposite direction.

-->  d. all of the above
``````

When you jump on a trampoline, the surface of the trampoline

``````a. changes shape.

b. exerts elastic force.

c. pushes you up into the air.

-->  d. all of the above
``````

counter force exerted by an elastic material that is stretched or compressed

``````-->  a. elastic force

b. stretching force

c. compressing force

d. elasticity

e. spring
``````

Elastic force causes an elastic material to

``````a. push back when pulled.

c. take the shape of its container.

-->  d. two of the above
``````

ability of a material to return to its original shape after being stretched or compressed

``````a. elastic force

b. stretching force

c. compressing force

-->  d. elasticity

e. spring
``````

Something that is elastic springs back after being stretched.

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

b. false
``````

An elastic material resists a change in shape.

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

b. false
``````

Elastic force is not very useful.

``````a. true

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

When you use a resistance band, resistance comes from elastic force.

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

b. false
``````

Glass is an example of an elastic material.

``````a. true

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

Items that are elastic include

``````a. metal wires.

b. concrete blocks.

-->  c. plastic spring toys.

d. all of the above
``````

When you compress a spring, it resists the change in shape.

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

b. false
``````

A rubber band keeps a newspaper tightly rolled because it

``````a. can be tied tightly.

-->  b. exerts elastic force.

c. is unbreakable.

d. none of the above
``````

Paper is an example of an elastic material.

``````a. true

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

When you compress a spring, it

``````-->  a. resists the change in shape.

b. exerts a force in the same direction.

c. permanently changes to a new shape.

d. two of the above
``````

As you stretch a bungee cord, its elastic force gets stronger.

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

b. false
``````

When you release a stretched bungee cord, it returns to its original shape because of gravity.

``````a. true

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

Springs are used in

``````a. beds.

b. cars.

c. scales.

-->  d. all of the above
``````

Something that is elastic returns to its original shape after being compressed.

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

b. false
``````

What happens when the stretching force on an elastic material is released?

``````a. The material breaks.

b. The material remains stretched out.

c. The material starts to exert elastic force.

-->  d. The material snaps back to its original shape.
``````

## diagram questions

No diagram questions associated with this lesson