6 Materials

Question 1

Name the two spring forces?

Answer 1

Tensile forces - producing an extension
Compression forces - producing a compression

Question 2

What regions are Hooke’s Law true?

Answer 2

Until the limit of proportionality - elastic limit of the material

Question 3

State Hooke’s Law

Answer 3

The extension of the spring is directly proportional to the force applied - as long as the elastic limit of the spring is not exceeded.

Question 4

What does the force constant measure?

Answer 4

F∝𝑥
Measure of stiffness of the spring
gradient of a force against extension graph

Question 5

What is elastic and plastic deformation?

Answer 5

Elastic deformation means that the spring will return to its original length when the force is removed. Plastic deformation means that it doesn’t go back to its original length.

Question 6

Formula for elastic potential energy

Answer 6

E= area under graph
E=1/2F𝑥
work done = average force x final extension

Question 7

Doubling extension does what to energy stored?

Answer 7

E=1/2k𝑥^2
Quadruples the energy stored.

Question 8

What happens to the length of a 1cm spring if put in series with another

Answer 8

Both have a 1cm extension

Question 9

What happens to the length of a 1cm spring if put in parallel with another

Answer 9

Shared the extension, both have 0.5cm extension

Question 10

Area of a force extension graph?

Answer 10

Work done (elastic potential energy)

Question 11

Difference between loading and unloading? Area of graph

Answer 11

Thermal energy
Loading is adding a force, unloading is removing a force.

Question 12

What does a hysteresis loop do/look like?

Answer 12

Elastic/ rubber graph of force against extension. Doesn’t have an elastic limit. Return to original shape after force removed - elastic deformation.

Question 13

Theory behind warming up rubber

Answer 13

Rubber consists of squashed and tangled long-chain molecules. Untangled easily with small forces, but need large forces to extend fully. Rubber is poor at storing energy - ideal material for impact forces.

Question 14

What does the force-extension graph look like for a metal?

Answer 14

loading=unloading until the elastic limit.

Question 15

What does the force-extension graph look like for a polythene?

Answer 15

Doesn’t follow Hooke’s Law - not straight proportional. Suffer plastic deformation with little force.

Question 16

Define tensile stress

Answer 16

Force applied per unit cross-sectional area of the wire.

Question 17

Define tensile strain

Answer 17

Fractional change in the original length of the wire

Question 18

Equation for tensile stress and strain

Answer 18

stress - σ=F/A
strain - ε= 𝑥/L

Question 19

Stress-Strain graph: Define P, E, Y1 and Y2, UTS, B

Answer 19

P - limit of proportionality
E - elastic limit (plastic deformation after this)
Y1 and Y2 - yield points, material extends rapidly with little stress.
UTS - ultimate tensile strength, maximum stress before it breaks.
B - breaking point, stress value at point of fracture.

Question 20

Define Young modulus

Answer 20

stress ∝ strain
gradient of the linear region of the stress-strain graph
measure of the ability of a material to withstand changes in length when under tension or compression.

Question 21

What is work hardening a material

Answer 21

Getting the material to the Y2 point on the graph for predictable use in structures.

Question 22

Define necking of a material

Answer 22

When the decreasing area increases the stress of the material after the point of Ultimate Tensile Strength

Question 23

What is Ultimate Tensile Stress equal to?

Answer 23

The stress value at that point - the force in σ=F/A.