Materials

Question 1

What is Hooke’s Law?

Answer 1

The force needed to stretch a spring is directly proportional to the extension of the spring until it reaches the limit of proportionality.

Question 2

What happens to the extension when there are springs in parallel?

Answer 2

Extension is halved as the load is shared

Question 3

What happens when there are two springs in series?

Answer 3

The length is doubled. The force is the same in each

Question 4

What is an elastic extension?

Answer 4

Returns to original shape when load removed.

Question 5

What is a plastic extension?

Answer 5

One that permanently deforms the material

Question 6

What is the elastic limit?

Answer 6

The point where an material will no longer return to its original length.

Question 7

Describe elastic potential energy.

Answer 7

Energy is stored in the stretched spring.

Question 8

Equation for energy stored in a spring

Answer 8

½ ke² or ½ Fe

Question 9

Equation for strain

Answer 9

Strain=extension/original length

Question 10

What is Young modulus?

Answer 10

The ratio of stress to strain for a given material,resulting from tensile forces,provided Hooke’s law is obeyed

Question 11

What happens when two springs are in series?

Answer 11

Springs experience same force, extension doubles

Question 12

Define tensile stress

Answer 12

The force exerted per unit cross-sectional area of a material

Question 13

Define tensile strain

Answer 13

The extension per unit length

Question 14

Explain why crumple zones keep passengers safe with the aid of plastic deformation.

Answer 14

When a car crashes some of the KE is absorbed in changing the shape of the material a crumple zone is made up of.
So less energy is transferred to the people inside making it safer.

Question 15

Outline an experiment to determine youngs modulus of a material. (RP4 - ON OUR A-LEVEL)

Answer 15

Take a Long (as possible) Thin (as possible) wire - Reduces uncertainty.

Find the cross sectional area using a micrometer - Take 3 readings at different points on the wire to find an AVG

Clamp the wire at one end of the bench, place the other end over a smooth pully and add mass to that end. (DO NOT INCLUDE IN YOUR FINAL CALCULATIONS)

Add a marker to the wire with a pen or sticky note.
Place a ruler underneath the part of the wire with the marker on it. Note down the position of the marker compared to the ruler. This is your initial “L”

Add mass at 100g intervals, Each time noting down the position of the marker in relation to the ruler.
This allows us to find ∆L (End Length - Start Length)

Then we can use πr2 to calculate the cross sec area.
Do force over area to find stress.

∆L / L for strain and dividing the two.

Question 16

After carrying out required practical 4, To determine stress and strain of a material. What analysis should be done? What is shown by the grad of the graph? What is shown by the area below?

Answer 16

Plot a graph of stress (y)
against strain (x)

The gradient is stress / strain = youngs mod.
The area under this graph shows strain energy per unit volume.

Question 17

What is meant by the yield point?

Answer 17

Here, the material suddenly starts to stretch without any extra load.

the yield point is the stress at which a large amount of plastic deformation takes place with a constant OR reduced load.

Question 18

What’s the difference between a stress strain graph and a force extension graph.

Answer 18

A stress strain graph DOES NOT depend on the object a material is made from (a copper pan and wire would be the same) a force extension is obvs different as it is not ratios.

Question 19

What is the area between the loading and unloading lines for a plastically deformed objects f/e graph?

Answer 19

Work done to deform the object.

Question 20

Why are brittle materials brittle?

Answer 20

They have a RIGID STRUCTURE

Question 21

Define the stiffness of a material.

Answer 21

The force needed to extend it by 1 meter

Question 22

What 2 things does hookes law apply to (For the sake of AQA A-Level physics)

Answer 22

Springs and metals
ONLY

Question 23

What are the key characteristics of an elastic stretch?

Answer 23

The material stretched will return to its original shape.
All work done (by stretching the spring) is converted into elastic strain (potential) energy
When the stretching force is removed this Elastic strain energy is converted into other types (i.e. Ke in an elastic band)

Question 24

What’s a plastic stretch?

Answer 24

When the material doesn’t return to its original length (1)
When all the work done is not converted to elastic potential energy, Some is done to pull the atoms apart from their original positions. (2)

Question 25

How do you calculate the work done on a material that is being stretched? What is it = to? What is the condition?

Answer 25

E = 1/2F∆L

Exactly equal to the work done on the material.

HAS TO BE OBEYING HOOKES LAW.