Materials

Question 1

What is the density of water?

Answer 1

1g cm^-3

Question 2

What is hooked law?

Answer 2

Force is proportional to extension

Question 3

What are the units of K?

Answer 3

Nm^-1

Question 4

What happens to k if springs are in parallel/series?

Answer 4

Parallel = k halves 
Series = k doubles

Question 5

When is stress positive or negative?

Answer 5

Tensile = positive 
Compressive = negative

Question 6

At what point does hookes law no longer apply?

Answer 6

Limit of proportionality (line no longer straight)

Question 7

What is the gradient on force extension graph?

Answer 7

K

Question 8

What happens at the elastic limit?

Answer 8

Plastic deformation (permanent extension)

Question 9

What happens in plastic deformation?

Answer 9

• Work done to separate atoms
• energy not stored as strain
• lost as heat

Question 10

What in elastic stuff?

Answer 10

• Energy stored as elastic strain energy
• when force is removed, energy is released
  Change is kinetic = change in potential

Question 11

What is area under stress strain graph?

Answer 11

Energy stored per unit volume

Question 12

Learn force against extension graph for an elastic stretch

Answer 12

Have fun

Question 13

What structure do brittle materials have?

Answer 13

Crystalline or polycrystalline

Question 14

Describe brittle materials

Answer 14

• have strong bonds = rigid and stiff

- when stress applied = cracks on surface get bigger until its snaps

Question 15

Describe what happens when stress applied to a metal

Answer 15

Atoms move to prevent cracks getting bigger and so aren’t brittle

Question 16

What do force against extension graphs depend on?

Answer 16

Materials dimensions

Question 17

Stress against strain graphs

Answer 17

Independent of dimensions (same for that material even if different dimensions)

Question 18

What is the yield point?

Answer 18

Point at which material stretches without extra load (lots of plastic deformation with reduced load)

Question 19

Derive energy stored from f-l graph

Answer 19

Area of a triangle and that

Question 20

What is elastic strain energy?

Answer 20

The work done stretching a material (its stored as potential)
- it’s the area under f-l graph

Question 21

Why doesn’t strain have units?

Answer 21

It’s a ratio

Question 22

Crumple zones?

Answer 22

Modern cars have areas called crumple zones so that the kinetic energy goes to changing shape rather than into the passengers (public transport have to balance these with safety of driver)

Question 23

(Stretched over elastic limit) why is the unloading line on force against extension graph parallel ?

Answer 23

The Ks are the same (area between loading and unloading = work done to permanently deform the wire)

Question 24

What are the units of Young’s modulus and stress?

Answer 24

Nm^-2 or Pa