I got an elastic band and hung it from a wooden spoon from the kitchen between two chairs. I tied a water bottle to the bottom of the elastic band. Then I put a washing up bowl underneath the bottle in case I spilled when I was pouring water into the bottle.
I wanted to do an experiment where I added masses to the end of the elastic band to make it stretch but we don't have masses at home. Then I remembered that 100 cubic cm (which is 100ml) has a mass of 100 grams. So I found the measuring jug in the kitchen.
To make sure that the measurement is ACCURATE you have to get down to eye level to view it. Remember that the middle of a liquid sinks - this is called the MENISCUS - so you see a double line for the liquid in the jug. The lower line is the meniscus and it is this line that needs to sit on the 100ml mark.
First I measured the length of the elastic band with no water in it.
Then I added 100ml of water and measured the length again. Then I added 100ml more and measured the length. I could do this all the way to 500ml.
We don't normally use length, we use extension. You calculate extension by subtracting the first length (the length with no water) from every other length.
Next I turned the mass in grams into force in Newtons and produced a graph.
Notice that the line doesn't go through the origin - the line is much steeper at the start but then goes straight. (If you add even more mass to it, the line will go very steep at the end.) The gradient of the graph is calculated by drawing a big right-angled triangle onto the line and calculating (delta y)/(delta x). The gradient is called the SPRING CONSTANT and in this case is measured in Newtons per cm because gradient is always y-axis units divided by x-axis units.
