Materials

Question 0

What is the equation for density?

Answer 0

Density = mass/ volume  
P = m/v

Question 1

Define Density

Answer 1

Mass per unit volume

Question 2

In words what does hooks law state?

Answer 2

That the extension of a wire, change in l is proportional to the force applied.

Question 3

As an equation what does hooks law state?

Answer 3

F= k x change in length .

Question 4

What is an objects stiffness constant ?

Answer 4

The force needed to extend it by 1m , it depends on the objects size an shape.

Question 5

Does hooks law work for compression?

Answer 5

Yes

Question 6

How do you calculate extension

Answer 6

New length - old length

Question 7

On a graph how do you know hooks law is being obeyed?

Answer 7

A straight line through the origin.

Question 8

What is the limit of proportionality?

Answer 8

The point beyond which the force is no longer proportional to the extension. The hooks law limit.

Question 9

What is the elastic limit?

Answer 9

The point at which the material will be permanently stretched and not return to the same size.

Question 10

If a material is stretched past its elastic limit it deforms …..

Answer 10

Plasticly

Question 11

Something that has undergone plastic deformation has …? What does this mean?

Answer 11

Gone past the elastic limit and so will not return to its original shape.

Question 12

Elastic deformation means that …

Answer 12

The material will return to its original shape.

Question 13

Why can materials stretch?

Answer 13

The atoms in the material can move small distances relative to their equilibrium positions without changing the structure of the material.

Question 14

Tensile stress is calculated by

Answer 14

Stress = force/ area

Question 15

What is strains units?

Answer 15

It has no units

Question 16

What is the equation for strain?

Answer 16

Tensile strain =

Change in length/ starting length

Question 17

What are the units for stress?

Answer 17

Nm^-2 or pascals, Pa

Question 18

What is breaking stress?

Answer 18

Stress that I large enough to break apart the material

Question 19

What is the maximum strength a material can withstand called?

Answer 19

Ultimate tensile stress (UTS)

Question 20

When an item is stretched, before the elastic limit where is the energy stored?

Answer 20

As elastic potential energy

Question 21

When a material is stretched what is the elastic potential energy called?

Answer 21

Elastic strain energy

Question 22

What is elastic strain energy?

Answer 22

the name for when a material is stretched and energy is stored as the elastic potential energy.

Question 23

What is the area under a stress strain graph?

Answer 23

Energy per unit volume

Question 24

How would you find the energy stored (work done) using a force/ extension graph

Answer 24

Find the area under the line, | 1/2 x force x change in length

Question 25

What is the equation. For energy stored in a stretched/compressed object? What is necessary for this to be true? (Graph)

Answer 25

Energy= 1/2 x force x change in length. | The material must be obeying hooks law.

Question 26

How can the energy stored equation also be written?

Answer 26

E=1/2k x L^2 | * F is replaced by Kl (hooks law)

Question 27

Points on how 1/2xFx delta L is derived. (Energy stored)

Answer 27

``` Energy stored = work done Work done = Fx delta L Graph is F by change in L area under graph is Energy Line is proportional and through 0 Triangle equation for area 0.5BH So energy stored is 1/2 x F x delta L ```

Question 28

What is the point where the material stretches without extra load being added called?

Answer 28

The yield point

Question 29

What is the youngs modulus of a material?

Answer 29

It is a measure of how stiff a material is, it makes it useful for comparing materials and calculating extension.

Question 30

What is the symbol for youngs modulus?

Answer 30

E

Question 31

How is Young's modulus calculated ( 2 equations)!

Answer 31

Stress / strain | FL/ A x change in length

Question 32

Describe an experiment to find the Young's modulus of a wire.

Answer 32

Set up a wire, fixed to a bench at one end and a pulley at the other. Make sure the wire is thin and long, so it extend more. Place a marker in the wire. And a mm rule underneath this. Start with the smallest possible weight to make the make the wire straight with no slack. This is the un-stretched length. Increase the weight in steps,recording the change in length from the marker to the start each time. Use a micrometer to measure the diameter if the wire. Take repeats and take an average to calculate the CS area. Use this data to calculate Young's modulus, E

Question 33

What could you use to calculate the cross sectional area?

Answer 33

Use a micrometer to find the diameter and then use pieR^2

Question 34

Energy per unit volume =

Answer 34

1/2x stress x strain | Area under a stress strain graph.

Question 35

How can you recognise a graph of a brittle material?

Answer 35

It follows hooks law with a straight line through the Pravin and then stops, it does not curve of deform plasticly, it snaps.

Question 36

What is 1mm^2 in metres

Answer 36

1 x 10 ^-6 M^2

Question 37

Describe the structure of a brittle material.

Answer 37

The atoms are often in a crystalline structure. In a brittle material the strong bonds and arrangement means that the atoms can not move much from their equilibrium position.

Question 38

Brittle fracture is when?

Answer 38

When stress is applied to a brittle material and tiny cracks at the materials surface get bigger and bigger until the material breaks.

Question 39

When stress is applied to a brittle material and the cracks grow and grow as the atoms can not move much, it is called?

Answer 39

A brittle fracture