Materials

Question 1

What is density?

Answer 1

Density is the mass of an object per unit volume of the object. Density = mass/volume.

Question 2

What is Hooke’s law?

Answer 2

The extension of a spring is proportional to the applied force up to the limit of proportionality of the spring.

Question 3

What is the spring constant?

Answer 3

The spring constant is the measure of the stiffness of a spring up to its limit of proportionality of the spring or elastic limit (the same thing).

Question 4

How does the total spring constant change for springs in series?

Answer 4

The total spring constant in parallel increases as the load isn’t shared between the 2, the springs extended further because they are both supporting the same stronger force.

Question 5

How does the total spring constant change for springs in parallel?

Answer 5

The total spring constant in parallel decreases as the load is shared between the 2 and doesn’t therefore extend as far.

Question 6

What is the limit of proportionality?

Answer 6

The limit of proportionality is the final value at which Hooke’s law applies to the springs.

Question 7

What is the elastic limit?

Answer 7

This is the maximum distance a material or spring can be stretched and still return to its original shape with no alteration.

Question 8

What is plastic deformation?

Answer 8

When the limit of proportionality is passed and the actual shape of the material is permanently changed.

Question 9

What is elastic deformation?

Answer 9

When the limit of proportionality isn’t breached and the material’s shape isn’t permanently changed.

Question 10

What is tensile stress?

Answer 10

Tensile stress is the force per unit cross-section area; for a wire of cross-sectional area A and under tension T, Tensile stress = T/A (Pascal, Pa or Nm^-2.

Question 11

What is the ultimate tensile stress?

Answer 11

The maximum tensile stress of a material can experience before breaking (and a change of cross-sectional area as a result) will occur.

Question 12

What does the Young Modulus measure?

Answer 12

A materials stiffness

Question 13

What happens to a material if you let go after it has been stretched past it’s elastic limit?

Answer 13

It will try to shrink hack or it’s original size but can’t as it has been plastically deformed.

Question 14

What are the key points on a stress-strain graph?

Answer 14

Limit of proportionality
Elastic limit
Yield stress
Ultimate tensile stress

Remember PEYU for the order above for when they appear on the graph.

Question 15

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

Answer 15

The Young Modulus, which is proportional up to the point of limit of proportionality.

Question 16

What does the area under the line represent on a stress-strain graph?

Answer 16

The strain energy per unit volume.

Question 17

How can you recognise a brittle material from its stress-strain graph?

Answer 17

A brittle material will have a steep gradient.

Question 18

How can you recognise a ductile material from its stress-strain graph?

Answer 18

It’ll have the highest plastic deformation, indicated by a long sloping gradient line.

Question 19

What key points are in a force against extension graph?

Answer 19

The limit of proportionality
The elastic limit
Yield stress
Ultimate tensile stress

Same as a stress/strain graph.

Question 20

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

Answer 20

The spring constant k.

Think Hookes law.

Question 21

What does the area under a force-extension graph show?

Answer 21

The work done in stretching the spring.
W=Fs
Work done = Force x distance

Question 22

Define’ tensile strain’

Answer 22

extension/original length = change in L/L