Materials

Question 1

Density of water

Answer 1

1g per cm^3 (1gcm^-3)

Question 2

Define Hookes law

Answer 2

The extension is directly proportional to the force applied up to the lim it of proportionality

Question 3

On a force extension graph, what is the gradient and what is the point called after it becomes linear

Answer 3

Gradient = spring constant
Point = Elastic limit (Hookes law only works before this point)

Question 4

For a springs in parallel, explain principles

Answer 4

Force is split between the two springs
Extension is the same for both springs
Force = F1 + F2 (K1L1+K2L2)
Keff = K1 = K2
Energy is conserved when stretching

Question 5

For springs in series, explain principles

Answer 5

Forces in spring is the same
Total extension = L1 + L2
Keff = (1/K1 + 1/K2)^-1

Question 6

Explain elastic deformation

Answer 6

Material can return to its original shape after force
Atoms are pulled apart but can move small distances whilst still in equilibrium
They then return to original positions
Only happens when below elastic limit

Question 7

Explain plastic deformation

Answer 7

Material is permanently stretched
Atoms move apart and can’t move back
Only happens after elastic limit

Question 8

Explain brittle

Answer 8

A material that fractures with little elastic deformation and no (little) plastic deformation

Question 9

Explain stiff

Answer 9

The extent to which an object resists deformation in response to an applied force (ratio of force to extension)

Question 10

Explain strong

Answer 10

Can take a lot of force before breaking

Question 11

Explain tough

Answer 11

Resists failure, after deformation (amount of energy before breaking)

Question 12

Explain malleable

Answer 12

Can be moulded by force

Question 13

Explain hardness

Answer 13

Can resist surface abrasions (scratches)

Question 14

Explain endurance

Answer 14

Can withstand repeated stress cycles

Question 15

Explain ductile

Answer 15

Able to plastically deform without breaking along its length

Question 16

What is meant by breaking stress

Answer 16

Stress big enough to break a material

Question 17

What is meant by ultimate tensile stress

Answer 17

Maximum stres a material can withstand

Question 18

On a force extension graph, what does the area under the graph represent

Answer 18

Elastic strain energy

Question 19

Explain a practical for Youngs Modulus

Answer 19

Setup: Wire, marker, pulley, weight, ruler
Method; Measure diameter of wire, 3x find average and find cross sectional area.
Measure length of wire from fixed end to marker
Add weights 100g per time and measure extension
Plot a graph of stress against strain
Line of best fit, gradient = E

Question 20

On a stress strain graph, name the 2 main points

Answer 20

Limit of proportionality (Until it stops being linear)
Yield point - material starts to stretch (stress at which plastic deformation takes place)

Question 21

Why doesn’t an unloading line on a stress strain graph doesn’t go through the origin

Answer 21

Material has plastically deformed (parallel to loading line)