Year 12 Young's Modulus of Wool Experiment

 I tied the wool around something heavy. The heavy object has been heavier than 500 grams because we'll be hanging 500 grams of water on the other end. I did consider tying it around the table leg on the far side. That would work. The length of wool has to be as long as you can make it.

 It helps if the end of the table is smooth. There must be as little friction as possible where the wool rubs over the table edge. Tie a knot in the wool at about 25cm from where it goes over the edge of the table. This will be our marker for measurements.

A bottle needs to be tied to the loose end of the wool and I'd advise putting a washing up bowl underneath to catch any drips.

 Once this is done, write down the position of the knot on the ruler. Get a measuring jug and fill it with 100ml of water. This is 100 grams.

Pour it carefully into the bottle. Write down the position of the knot on the ruler scale and calculate the extension of the wool (how much it has stretched). Repeat until you have done 200 grams, 300 grams, 400 grams, 500 grams. You need a table that records mass, weight and extension.
Finally carefully pour the water from the bottle back into the jug trying to disturb the wool as little as possible. Take a reading of the unloaded position again. You should find that it hasn't gone quite back to its original position. There is a slight permanent deformation in the wool.
You need to measure two other things:
1. The diameter of the wool.

Calculate the cross-sectional area A of the wool in square metres.

 2. The total length of the wool from the bottle along. I included all of the wool that was tied around my dumbbell because all of that wool stretched as well.
This is L, the length of the wool. Write it in metres.

Here are some bits of the formula sheet

Plot a graph of force on the y-axis against extension on the x-axis. It should curve at the beginning but draw a best fit line through the straightest section further on.

Calculate the gradient and explain why the gradient is the spring constant k.

Change the units so that the spring constant is in Newtons per metre

I then combined four of the above equations. 

Use your gradient along with L and A to calculate a value for the Young Modulus of wool in Newtons per square meter. It will be a very big number.

Calculate the biggest %U for the measurement of the water volume. 

Explain why this gives us the biggest %U for force F.

Calculate the biggest %U for extension.

Calculate the %U for the diameter. (What does it mean if it comes out as 100%, which it might here?)

Explain why we have to double it to get the %U for A.

Calculate the %U for length L.

Now explain why we have to add %U for F, extension, A and L to get %U for the Young Modulus.

How many significant figures can we justify for our answer for the Young Modulus given the total %U?

Calculate the +- absolute error in the Young Modulus.

Comment on any problems in the experiment and how you overcame them.

State any control variables and their values. Comment on whether it is realistic to say that they actually remain constant during the experiment.

Give URL and date accessed for any web pages used.