Materials

Question 1

What is the formula for density?

Answer 1

p =m/V

Question 2

What are the units for density?

Answer 2

kgm^-3 or gcm^-3

Question 3

What is the definition of density?

Answer 3

Density is the mass per unit volume

Question 4

What determines whether an object will float or sink on a fluid?

Answer 4

Whether the object is more dense than the fluid (it will sink) or less dense than the fluid (it will float),

Question 5

What does Hooke’s law state?

Answer 5

The extension of a stretched wire, ΔL, is proportional to the load or force F.

Question 6

How can Hooke’s law be written as a formula?

Answer 6

F = kΔL

Where:

F is the force applied (N)

k is the spring constant (Nm^-1)

ΔL is the extension (m)

Question 7

Hooke’s law applies to both stretched wires and stretched and compressed ______

Answer 7

Springs

Question 8

The limit of proportionallity is…

Answer 8

The point up to which Hooke’s law is obeyed.

Question 9

The elastic limit of a material is ……..

Answer 9

The point after which the material will become permanently deformed.

Question 10

Elastic deformation means…..

Answer 10

The material will return to its original shape once the forces are removed.

Question 11

Plastic deformation means…..

Answer 11

The material will not return to it’s original length once the forces are removed.

Question 12

If a pair of opposite forces stretch a material, they’re called ______ forces.

Answer 12

If a pair of opposite forces stretch a material, they’re called tensile forces.

Question 13

If a pair of opposite forces compress a material, they’re called ______ forces.

Answer 13

If a pair of opposite forces compress a material, they’re called compressive forces.

Question 14

Tensile stress is defined as…..

Answer 14

the force applied, F, divided by the cross-sectional area, A:

Stress = F/A

Question 15

What are the units of tensile stress?

Answer 15

Nm^-2 or Pascals, Pa

Question 16

Tensile strain is defined as…….

Answer 16

The change in length divided by the original lengeth of the material.

Question 17

What are the units of tensile strain?

Answer 17

They don’t have units as it’s a ratio.

Question 18

What is the breaking stress of a material?

Answer 18

This is the stress that is big enough to break the material.

Question 19

What is the ultmate tensile strength stress of a material?

Answer 19

Ultimate tensile strength is the maximum stress that the mateiral can withstand.

Question 20

What is elastic strain energy?

Answer 20

It is the potential energy stored when a material is stretched (before the elastic limit is met).

Question 21

What does the area under a force-extension graph tell you?

Answer 21

The elastic strain energy

Question 22

What is the formula for calculating elastic strain energy?

Answer 22

E = 1/2 k (ΔL)²

Question 23

What does the gradient of a force - extension graph tell you?

Answer 23

The gradient of a force-extension graph is the spring constant k, which has units Nm^-1

Question 24

How is energy conserved as a stretched wire undergoes plastic deformation?

Answer 24

When a material undergoes plastic deformation, energy is used to move atoms in the material away from each other. This energy is dissipated as heat.

Question 25

Describe the energy changes in a spring as it is stretched and released.

Answer 25

When a spring is stretched, kinetic energy is transferred to elastic strain energy and stored in the spring. When the spring is released, the elastic strain energy is transferred to kinetic energy.

Question 26

Which point on the graph shows the ultimate tensile strength?

Answer 26

E

Question 27

Which point on the graph shows the elastic limit?

Answer 27

B

Question 28

Which point on the graph shows the breaking point?

Answer 28

F

Question 29

Which point on the graph shows the limit of proportionality?

Answer 29

A

Question 30

Name the law that says the extension of a stretched object is proportional to the force applied?

Answer 30

Hooke’s Law

Question 31

What is the difference between elastic deformation and plastic deformation?

Answer 31

If a material undergoes elastic deformation, the material will return to its original shape and size once the load is removed. Whereas, if the material undergoes plastic deformation, the material will not return to its original shape and size once the load is removed.

Question 32

True or false? The stress-strain graphs of two different sized pieces of nickel have the same gradient.

Answer 32

True. The gradient of a stress-strain graph is equal to the Young modulus of the material. Both pieces are made from the same material, so will have the same Young modulus and therefore the same gradient.

Question 33

Why is it better to use a longer wire when using a wire to find the Young modulus?

Answer 33

The longer the wire, the bigger the extension for a given force. A bigger extension is easier to see and measure, and it reduces the uncertainty in the measurements.