Chapter 3.4 - Materials

Question 1

Elasticity

Answer 1

The property of a body to return to its original shape once the deforming force is removed

Question 2

Deformation

Answer 2

The change in shape or size of an object

Question 3

Elastic Deformation

Answer 3

An object that deforms that will return to its original shape once the deforming force is removed

Question 4

Plastic Deformation

Answer 4

When an object deforms and then when the deforming force is removed the object remains deformed

Question 5

Tensile force

Answer 5

Creates tension in an object and will result in an extension

Question 6

Compressive force

Answer 6

A force that causes an object to compress

Question 7

What a force extension graph will look like for a metal

Answer 7

Will start of straight. Then the limit of proportionality is reached and the gradient will start to change. Then the elastic limit is reached and it will extend more per unit force (gradient decreases) until it reaches the point of fracture

Question 8

Experiment to observe force-extension of a wire

Answer 8

Clamp a wire on one end of a table and attach a weight on the other end. The weight should dangle off the table and the wire should be placed over a pulley. Attach a marker to the wire and fix a ruler in position. Add more mass to the weight and record how much the wire extends

Question 9

Hookes Law

Answer 9

The extension of an object is proportional to the force that causes it, provided that the elastic limit is not exceeded

Question 10

Force constant of a spring

Answer 10

The force required to extend the spring by one unit length

Question 11

Hookes law in equation form

Answer 11

F=kx

Question 12

Area under a force-extension graph

Answer 12

Work done to stretch the object

Question 13

What happens to the work done put into stretching a wire that exceeds its elastic limit

Answer 13

• At first the work done is causing an increase in elastic potential energy
• Once the material has exceeded its elastic limit the rest of the energy that is input will be converted to heat

Question 14

Stress

Answer 14

Force per unit cross sectional area

Question 15

Strain

Answer 15

Extension per unit length

Question 16

Ultimate tensile strength

Answer 16

The maximum stress that an object can endure before breaking

Question 17

Equation for youngs modulus

Answer 17

Tensile stress / Tensile strain

Question 18

Young Modulus

Answer 18

A measure of the stiffness of a material

Question 19

The overall force constant of two springs in series

Answer 19

1/k = 1/(k1) + 1/(k2)

Question 20

The overall force constant of two springs in parallel

Answer 20

k = (k1) + (k2)

Question 21

How to work out the ultimate tensile strength from a stress-strain graph

Answer 21

The highest point on the graph

Question 22

Experiment to determine Young’s Modulus of a wire

Answer 22

Clamp one end of a wire and attach a weight to the other end. Run the wire over a pulley and mark a point on the wire. Measure the distance from the clamp to the marking. Measure the diameter of the wire with a micrometer and calculate its cross sectional area. Increase mass on the weight and at each step record the extension of the wire. Plot the stress against strain and the YM will be the gradient

Question 23

Stress-Strain graph of a ductile material

Answer 23

At first it is straight and obeys Hooke’s Law.
Then the limit of proportionality is reached and the gradient starts to decrease.
The elastic limit is reached and the gradient continues to decrease.
The yield point is reached and the gradient goes negative for a short while before gradually increasing

Question 24

Elastic limit

Answer 24

The maximum stress an object can endure while still behaving elastically. After this point it will not return to its original shape

Question 25

Stress-Strain graph for a brittle material

Answer 25

Straight line then breaks

Question 26

Stress-Strain graph for a polymeric material

Answer 26

Look in the book its hard to explain

Question 27

What the area under (or within) a stress strain graph is

Answer 27

The energy per unit volume