Unit 4 - Materials

Question 1

Define density

Answer 1

The mass per unit volume of a material

Question 2

What two factors affect density?

Answer 2

The concentration of atoms and the intrinsic mass of these atoms

Question 3

How do you work out the density of a material that is made up of two or more other materials?

Answer 3

1. Total Mass/Total Volume
2. Use the density and percentage volumes of the individual materials to calculate the overall density of the final material

Question 4

Define extension

Answer 4

The amount of stretch a spring experiences when a tensile stretching force is applied to it

Question 5

T/F: Extension is directly proportional to the tensile stretching force applied

Answer 5

True, up to a limit

Question 6

What is Hooke’s Law?

Answer 6

Hooke’s law expresses the idea that the extension is directly proportional to the tensile stretching force applied to it. This is where the equation: F = k x e comes from.

Question 7

What will happen to the extension of a spring if the spring constant decreases?

Answer 7

The extension will increase

Question 8

What happens to the displacement when two springs are added in parallel?

Answer 8

The displacement will be half that of one spring with the same force applied

Question 9

What happens to the displacement when two springs are added in series?

Answer 9

The displacement will be double that of a single spring with the same force applied

Question 10

What does the gradient of a force-extension graph show?

Answer 10

The spring constant

Question 11

What is the area under a force-extension graph equal to?

Answer 11

The work done when stretching the spring: Work Done = 1/2Force x Extension

Question 12

What is stress?

Answer 12

Stress is equal to the force per unit area within a material

Question 13

What is strain?

Answer 13

The extension per unit length of a material

Question 14

What does the gradient of a stress-strain graph equal?

Answer 14

The Young’s Modulus of the material

Question 15

How do we use stress and strain?

Answer 15

We can use stress and strain to compensate for the effect that thickness and length have on the property of a material

Question 16

What is the area under a stress-strain graph equal to?

Answer 16

The energy per unit volume of a material: 1/2 x Stress x Strain

Question 17

What are the 5 important points on a stress-strain graph?

Answer 17

1. P - limit of proportionality
2. E - elastic limit
3. Y - yield points
4. UTS - ultimate tensile stress
5. BP - breaking point

Question 18

What does a metals stress-strain graph look like?

Answer 18

Linear up to the limit of proportionality when the gradient decreases and it curves

Question 19

How does rubber react to a tensile stretch force being applied to it?

Answer 19

Stretches easily at first and then stiffens and becomes harder to stretch

Question 20

How does polythene react to a tensile stretch force being applied to it?

Answer 20

Difficult to stretch at first before yielding and becoming easier to stretch and then stiffening again

Question 21

What does it mean if a material behaves elastically?

Answer 21

It will return to its original shape after being deformed

Question 22

What does it mean if a material behaves plastically?

Answer 22

It will not return to its original shape after being deformed

Question 23

Can materials behave elastically and plastically?

Answer 23

Yes, materials often behave elastically up to the elastic limit, if we load a material beyond that it will not return to its original shape

Question 24

T/F: Changing the length of the wire or the width of the wire does not affect the extension

Answer 24

False, changing either of these factors will cause the extension to change

Question 25

What is the opposite of a tensile force?

Answer 25

A compressive force

Question 26

T/F: The Young’s Modulus of a material does not have a unit, it is dimensionless

Answer 26

True

Question 27

What is the ultimate tensile stress?

Answer 27

The maximum stress a material can withstand before deforming rapidly to the breaking point