Module 3 - Section 4 - The Youngs Modulus

Question 1

What is Youngs Modulus ?

Answer 1

Youngs Modulus = tensile stress / tensile strain

E = F/A / x/L = Fl / xA

It is a measure of the stiffness of a material

Question 2

How is the Young’s modulus used by engineers ?

Answer 2

It is used by engineers to make sure their materials can withstand sufficient forces

Question 3

How do you do the Youngs Modulus experiment ?

Answer 3

First the set up:
You set up everything on a table
You need 2 clamps: one clamps the end of a wire to keep it in place, the other one clamps the pulley, you also need weights, a long and thin test wire, ruler with mm markings and a marker

Then you need to find the cross-sectional area of the test wire - to do this use a micrometer to measure the diameter in many places on the wire and then get an average result for the diameter - then by assuming that the cross - section is circular we could use pie r *2 to find out the cross sectional area of the wire

Then clamp the test wire to the bench, then add a weight to the end of the pulley ( wire ) to straighten out the wire but DONT include this in your calculations

Then use a marker to mark a place towards the start of the ruler ( away from the pulley ) then measure the distance between the marker on the wire and the fixed end of the wire - this is your unstretched length

Then you increase the weight - this should make the wire stretch and make the marker move along the ruler - record the marker reading each time you add weight - add weight in 1N intervals and record the stretch - the extension is the difference between the original length and the reading

Use digital scales to measure the weight you add each time

Then use your results from the experiment to find out the stress and strain of the wire and you can use this to calculate the young modulus of the wire - you can also plot a stress-strain graph

*also when you take the weight off, measure the extension for each weight to make sure that you haven’t gone past the wires elastic limit

Question 4

Why should you get a wire that is very long and thin for the Young’s modulus experiment ?

Answer 4

The test wire should be thin and as long as possible - as the longer/thinner the wire is - the more it extends for the same force - this will reduce uncertainty in your measurements

Question 5

What can you do to reduce random errors in the Young’s modulus experiment ?

Answer 5

To reduce random errors you should use thin marker on the wire, and always look from directly above the marker and ruler when measuring the extension of the wire

Question 6

What are the safety measures of the Young’s modulus experiment ?

Answer 6

When your doing the experiment, you should be standing up just in case the weights fall and you have to get out of the way quickly

And wear safety goggles just in case the wire snaps and hit you in the eyes

Question 7

Whats does the gradient of an stress-strain graph give you ?

Answer 7

The gradient of a stress strain graph gives you the Youngs Modulus, E

Question 8

What does the area under a stress/strain graph give you ?

Answer 8

It gives you the elastic potential energy per unit volume - the energy stored per 1m*3 of wire

Question 9

How can you figure out the energy per unit volume from a stress/strain graph ?

Answer 9

Energy per unit volume = 1/2 stress x strain

Question 10

What’s the units for Young’s modulus ?

Answer 10

Nm*-2 or Pa