Materials

Question 1

What is density?

Answer 1

A measure of how compact a substance is.

Question 2

What is the equation for density?

Answer 2

ρ = m / v

ρ = density, Pa or Nm-2
m = mass, kg
v = volume, m3

Question 3

1gcm-3 = ?kgm-3

Answer 3

1000

Question 4

Do elastic objects object Hooke’s law all the time?

Answer 4

No, if they extend too much Hooke’s law stops being true.

Question 5

What is the limit of proportionality?

Answer 5

Last point where Hooke’s law applies.

Question 6

What happens beyond the elastic limit?

Answer 6

The material won’t return to its original length once force equals zero.

Question 7

What is the deformation after the elastic limit?

Answer 7

Plastic.

Question 8

What is the deformation before the elastic limit?

Answer 8

Elastic.

Question 9

What is the equation for elastic potential energy?

Answer 9

U = 1/2 k ΔL^2

U = EPE, J
k = spring constant, Nm-1
ΔL = extension, m

Question 10

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

Answer 10

Elastic potential energy stored.

Question 11

Define pressure.

Answer 11

The force applied per unit area.

Question 12

What is the equation for pressure?

Answer 12

F = A P

F = Force, N
A = Area, m2
P = Pressure, Nm-2 or Pa

Question 13

Define stress.

Answer 13

The force per unit area.

Question 14

What is the equation for stress?

Answer 14

Stress = F/A

Stress, Nm-2 or Pa
F = Force, N
A = Area, m2

Question 15

Define strain.

Answer 15

The extension per unit length.

Question 16

What is the equation for strain?

Answer 16

Strain = ΔL / L

ΔL = extension, m
L = original length, m

Question 17

What are the units for strain?

Answer 17

No units.

Question 18

What is the equation for Young’s Modulus?

Answer 18

E = stress/strain

E = Young’s Modulus, Nm-2 or Pa

Question 19

If E is small what does this mean?

Answer 19

The material stretches easily.

Question 20

If E is big what does this mean?

Answer 20

The material is difficult to stretch.

Question 21

When does Young’s Modulus change?

Answer 21

When a material is heated.
When a material stretches beyond its elastic limit.

Question 22

What is the equation for Young’s Modulus where stress and strain are broken up into their respective equations?

Answer 22

E = F L / A ΔL

Question 23

What is the equation linking the spring constant and Young’s Modulus?

Answer 23

k = E A / L

Question 24

Is k constant for a material?

Answer 24

No, it depends on thickness and length of the material.

Question 25

On a stress-strain graph what is the gradient?

Answer 25

E

Question 26

What is the area under a stress-strain graph?

Answer 26

Energy per unit volume.

Question 27

Define breaking stress

Answer 27

Stress that breaks the material.

Question 28

Define ultimate tensile stress.b

Answer 28

The maximum stress a material can take and recover from.

Question 29

Define yield point. Where is it on a graph?

Answer 29

Where material continues to extend with significant plastic deformation even if the load is nearly constant.
The point before it dips, before the breaking point.

Question 30

Do brittle materials deform plastically?

Answer 30

No, they just break.