Materials

Question 1

State Hooke’s Law

Answer 1

Force is directly proportional to extension, up to the limit of proportionality

Question 2

What is the stiffness constant, k, dependent on?

Answer 2

How stretched an object is

Question 3

What is the limit of proportionality?

Answer 3

The point beyond which force is no longer proportional to extension

Question 4

What is the elastic limit?

Answer 4

The force beyond which a material will be permanently stretched

Question 5

What is the yield point?

Answer 5

The stress beyond which a material becomes plastic

Question 6

Define elastic deformation

Answer 6

The object will return to its original shape when the deforming force is removed

Question 7

Define plastic deformation

Answer 7

• The object will not return to its original shape when the deforming force has been removed
• Extension will be permanent

Question 8

Define tensile force

Answer 8

A force which stretches an object

Question 9

Define compressive force

Answer 9

A force which squashes an object

Question 10

Define tensile stress

Answer 10

Force applied, divided by the cross-sectional area, in N/m² or Pascals

Question 11

Define tensile strain

Answer 11

Extension, divided by the original length of the materail, no units

Question 12

Define breaking stress

Answer 12

The maximum tensile force that can be applied to an object before it breaks

Question 13

What is elastic strain energy?

Answer 13

The potential energy stored in a stretched material from work being done to stretch the material

Question 14

What happens to the stored elastic strain energy in a spring when the tensile force is released

Answer 14

The stored elastic strain energy is transferred to kinetic energy and gravitational potential energy
- The spring then compresses and kinetic energy is transferred back to elastic strain energy

Question 15

What is the conservation of energy equation for an oscillating spring?

Answer 15

Change in kinetic energy = change in potential energy

Question 16

Describe how energy conservation is used in transport design

Answer 16

• Cars are designed with crumple zones that deform plastically in a crash
• This means some of the car’s kinetic energy is transferred into changing the shape instead of the inside, increasing safety

Question 17

What is the Young Modulus?

Answer 17

The measure of how stiff an object is, up to the limit of proportionality

Question 18

What does the gradient of a Stress-Strain graph represent?

Answer 18

The Young Modulus, E

Question 19

What does the area under the graph of a Stress-Strain graph represent?

Answer 19

Strain energy per unit volume

Question 20

What is a brittle material?

Answer 20

A material which doesn’t deform plastically, but snaps when the stress on it reaches a certain point

Question 21

Define brittle fracture

Answer 21

When a stress applied to a brittle material causes small cracks on the material’s surface to get larger until the material breaks completely

Question 22

What is on the axes for a graph showing loading and unloading of an elastic material?

Answer 22

• x axis = Extension
• y axis = Force