The Young Modulus & Stress-Strain and Force-Extension Graphs

Question 1

What is the Young Modulus Equation?

Answer 1

Stress / Strain

Question 2

Up to the limit of proportionality the stress and strain of a material are […………..] to each other.

Answer 2

Proportional

Question 3

Where is the Young Modulus measured?

Answer 3

Below the limit of proportionality

Question 4

What are the units of Young’s Modulus?

Answer 4

Nm-2 (Pa) The same as stress

Question 5

What is Young’s Modulus a measure of?

Answer 5

Is a measure of the stiffness of a material

Question 6

Describe the experiment conducted to find the Young Modulus of a wire.

Answer 6

1 - Wire should be long and thin as it reduces percentage uncertainty of results 2 - Find cross-sectional area of wire using a micrometer to find diameter in multiple places. Use πr*2 to find the area of the circle 3 - Clamp wire to the bench 4 - Add smallest weight to straighten wire 5 - Measure this length between marker and fixed end of wire because this is the unstretched length 6 - Increase weight to stretch wire 7 - Increase weight in equal steps and record marker each time 8 - Use results to calculate stress strain and plot a stress strain curve.

Question 7

What is the gradient of a Stress / Strain graph?

Answer 7

Young Modulus

Question 8

What is the area underneath a Stress / Strain graph?

Answer 8

Elastic strain energy per unit volume

Question 9

Describe what happens when a material reaches the limit of proportionality.

Answer 9

• Graph is no longer a straight line and starts to bend. - At this point material stops obeying Hooke’s Law but would STILL RETURN TO ORIGINAL shape if the stress was removed

Question 10

Describe what happens when a material reaches the elastic limit.

Answer 10

• Material starts to behave plastically - From this point onwards the material would no longer return to its original shape once stress is removed

Question 11

Describe what happens when a material reaches the Yield Point.

Answer 11

• Here material starts to suddenly stretch without any extra load - Is the stress at which a large amount of plastic deformation

Question 12

Stronger materials can withstand [……] stress before they break

Answer 12

More

Question 13

What stress values do stronger materials have?

Answer 13

Higher breaking stresses

Question 14

Materials with high Young Modulus’ are…

Answer 14

Stuff materials (difficult to stretch or compress)

Question 15

What is Point P on this Stress-Strain graph?

Answer 15

Is the Limit of Propportionality

Question 17

What is Point E on the Stress-Strain Graph?

Answer 17

The elastic limit

Question 18

What is Point Y on the Stress-Strain Graph?

Answer 18

Yield Point

Question 19

Graph showing stiff and strong materials in comparison to weak and less stiff materials.

Answer 19

Question 20

Diagram of the apparatus used to find the Young Modulus of a wire.

Answer 20

Question 21

What is the difference between a force-extension graph and a stress-strain graph?

Answer 21

• Force-extension graphs are specific to material and depend on its dimensions
• Stress-Strain graphs describe the general behaviour of a material

Question 22

Describe what is happening in this graph.

Answer 22

• Wire has been stretched beyong its limit of proportionality (P) so graph starts to curve
• When the load is removed extension decreases
• Unloading line is parallel to the loading line because the stiffness of the wire is the same
• The wire is stretched beyond its elastic limit (E) and deformed plastically, it has been permenantly stretched.
• The area between the two lines is the work done to permenantly deform the wire.