Materials

Question 1

What is hooke’s law and the equation

Answer 1

That extension (x) is directly proportional to force

F=kx K=force constant (Nm⁻¹) X=extension

Question 2

What are tensile forces

Answer 2

They are extensional forces

Question 3

What are compressive forces

Answer 3

Compressional

Question 4

What is elastically behaving

Answer 4

Up to a certain extension if the same force is removed the spring will return to its original length.

Question 5

What is Elastic limit

Answer 5

If this critical extension is exceeded the spring will be permanently stretched

Question 6

What is plastic behaviour

Answer 6

When hooke’s law is no longer behaved by the spring

Question 7

What is elastic stain energy

Answer 7

Is the potential energy stored when a spring or wire is stretched

Question 8

How to find Elastic stain

Answer 8

Area under the curve in a force against extension graph

E=0.5Fx
E=0.5kx²

Question 9

How to investigate force extension

Answer 9

Set up a clap stand and suspend a spring with a ruler next to it.
Add weights to the spring and calculate extension.
Plot force against extension, where the line is straight hooks law is being obeyed.

Question 10

Equation for tensile stress

Answer 10

σ=F/a (Nm⁻²)

Question 11

Equation for tensile strain

Answer 11

ε=x/l (no units)

Question 12

Equation for Young’s modulus

Answer 12

Young modulus = tensile stress/ tensile strain
= σ÷ε

Is a measure of elasticity

Question 13

How to find Young’s modulus

Answer 13

• Find the cross section of the wire using a micrometer.
• Clamp a wire to a bench so you can hang wires off one end.
• Start with a small weight to keep the wire taught.
• Measure the distance between the fixed end and the marked wire, this is your unstretched length.
• As you increase weight the further it will stretch.
• Then plot a stress against strain graph and the gradient will be Young’s modulus

Question 14

Labels in stress strain curves

Answer 14

P=limit of proportionality = stress is proportional to strain
E= elastic limit
Y1= yield point where the wires weaken temporarily
Y2= a small increase in stress causes a large increase in strain as wire undergoes plastic flow
UTS= ultimate tensile stress = the wire looses its strength, extends and becomes narrower.

Question 15

Stress strain curves for brittle material

Answer 15

The graph is a straight line, however when stress reaches a certain point it snaps

Question 16

Stress strain for ductile

Answer 16

Typical stress stain curve.

They keep there strength when they deform.

Question 17

Stress stain curves for polymeric materials

Answer 17

Leaf like shape.
The area between loading and unloading is the amount of energy converted to heat.
Loading is different to unloading because some energy is converted into heat.
Rubber returns to it original length, it behaves elastically.