Materials

Question 1

Define density

Answer 1

Mass per unit volume

Question 2

What is the equation for density

Answer 2

ρ = m/v

Question 3

Why is density an intrinsic property

Answer 3

As it won’t ever change for a given material.

Question 4

Convert gcm^-3 to kgm^-3

Answer 4

1 gcm^-3 = 1000 kgm^-3

Question 5

What is deformation

Answer 5

Deformation is when forces cause an object to change shape.

Question 6

What are the 3 different ways deformation can occur

Answer 6

1. Extension
2. Compression
3. Bending

Question 7

What is extension

Answer 7

The object increases in length
Defined as a positive change in length
Caused by tensile forces (tension)
The forces act outwards on the object

Question 8

What is compression

Answer 8

The object decreases in length
Defined as a negative change in length
Caused by compressive forces
Forces act inwards on the object

Question 9

What is bending

Answer 9

Object does not change overall size
Object is distorted
Must be 2 forces applied on the same size

Question 10

What is Hooke’s law?

Answer 10

The change in length of an object is directly proportional to the force applied up to the limit of proportionality.
F ∝ ΔL or F = kΔL

Question 11

What is k in the equation F = kΔL

Answer 11

k is a constant called the spring constant or stiffness constant
It hase the units Nm^-1
It is specific to a certain srping or wire (not a material)

Question 12

What is the equivalent spring constant for springs in series

Answer 12

1/k = 1/k₁ + 1/k₂

Question 13

What is the equivalent spring constant for springs in parallel

Answer 13

k = k₁ + k₂

Question 14

What is elastic deformation

Answer 14

When the material returns to its original shape and size when the forces are removed
The material is behaving elastically
Elastic deformation can only happen up to the elastic limit of the object

Question 15

What is plastic deformation

Answer 15

The material doesn’t return to original shape and size when the forces are removed
It is permanently deformed and is behaving plastically
This happens beyond the elastic limit

Question 16

What is elastic strain energy

Answer 16

Work done to deform a material before the elastic limit is reached
This energy is stored in the material

Question 17

How do you calculate elastic strain energy

Answer 17

1. Area under the graph in a force-extention graph
2. E = 1/2 FΔL
3. E = 1/2 k(ΔL)²
   (as long as limit of proportionality hasn’t been reached)

Question 18

What energy changes happen during loading

Answer 18

Work is done by the force on the material
This energy is stored in the material
This is equal to the area under the loading curve

Question 19

What energy changes happen during unloading

Answer 19

Work is done by the material (to regain its shape)
This energy is recovered (and dissipated to surroundings)
This is equal to the area under the unloading curve

Question 20

What is the internal energy of a material

Answer 20

Energy transferred during loading - energy lost during unloading
Internal energy is stored in the material (makes it heat up)
Internal energy is equal to the area enclosed by the loading and unloading curves