6.10 Elasticity, Spring Constant, & Hookes Law

Question 1

When you apply forces to an object it can be stretched, compressed or twisted. What is this?

Answer 1

Deformation

Question 2

To deform an object, how many forces do you need?

Answer 2

At least two

Question 3

What can you call an object if it returns to its original shape after the forces are removed?

Answer 3

You can say the object is elastic and it has been elastically deformed

Question 4

What can you call an object if it doesn’t return to its original shape when you remove the forces?

Answer 4

The object has been plastic and has been plastically deformed

Question 5

What can you explain both elastic and plastic deformation with?

Answer 5

The particle model of matter

Question 6

What happens in elastic deformation?

Answer 6

Solids are held in fixed shapes due to the forces between their particles. During elastic deformation the separation between particles changes so the forces between them also change. However, once the applied force has been removed, the particles return to their original positions within the substance

Question 7

What happens in plastic deformation?

Answer 7

In plastic deformation, the separation and forces between particles change. However, the applied forces are too large, so when they’re removed the particles don’t return to their original positions. The object is permanently deformed

Question 8

What is meant by extension?

Answer 8

The increase in length of a spring when its stretched

Question 9

How do we work out extension?

Answer 9

Measure how the spring’s length changes as we add downwards force

Question 10

When a material is supported at the top, why would the natural length be shorter than the whole length of the material?

Answer 10

The material’s own mass would be exerting a force downwards in the form of weight

Question 11

Why does the spring not fall down when we add any mass?

Answer 11

The solid support will also be exerting an equal but opposite force upwards and this is why the spring doesn’t fall down when we add any mass. It’s being perfectly balanced by the support

Question 12

What happens to the extension when we add more mass?

Answer 12

It increases proportionally

Question 13

What is the amount of extension for a given force made dependent on?

Answer 13

The object’s spring constant, which is noted by the letter k

Question 14

What does the spring constant of an object tell us?

Answer 14

How many newtons it would take to stretch the object by 1m

Question 15

If a material is supported at the top and a mass is attached to the bottom, it stretches. In some cases, e.g. a spring, this relationship is linear. What does this mean?

Answer 15

The extension (or compression) of the stretched material is directly proportional to the load or force applied

Question 16

The relationship between the extension of a material and the force is called Hooke’s law. What is the equation for this?

Answer 16

force exerted by a spring (N) = extension (m) x spring constant (N/m)

Question 17

What does it mean when a spring and mass are in equilibrium (i.e. the spring isn’t stretching any further)?

Answer 17

The force applied on the spring (the weight of the mass) is equal to the force exerted by the spring upwards on the mass

Question 18

What is an example of an object that behaves non-linearly?

Answer 18

Rubber bands

Question 19

If a material is supported at the top and a mass is attached to the bottom, it stretches. In some cases, e.g. rubber bands, this relationship is non-linear. What does this mean?

Answer 19

The force is not proportional to extension

Question 20

What is important to remember about elasticity and Hooke’s law?

Answer 20

That being ‘elastic’ doesn’t mean an object obeys Hooke’s law. Rubber bands are elastic objects. They return to their original shape when released, but they DON’T obey Hooke’s law

Question 21

In a force/extension graph, the larger the spring constant the __________ the gradient

Answer 21

steeper

Question 22

On a force/extension graph, how do you know if the object’s extension obeys Hooke’s law?

Answer 22

The line will be straight and the force and extension will be directly proportional

Question 23

On a force/extension graph, how do you know the object’s extension doesn’t obey Hooke’s law?

Answer 23

The line will be curved and the spring will stretch more for each unit increase in force

Question 24

On a force/extension graph, what is the gradient of a straight line equal to?

Answer 24

The spring constant of the object

Question 25

What is the point on a force/extension graph called where the line starts to curve?

Answer 25

Elastic limit or the limit of proportionality

Question 26

On a force/extension graph, what happens after the elastic limit or limit of proportionality?

Answer 26

Hooke’s law no longer applies and the object wont necessarily go back to its original shape, meaning that it will have been permanently deformed

Question 27

Applying forces to an object can cause it to: (3)

Answer 27

• Bend
• Compress
• Stretch