To do this experiment you need a plastic container, some tins of food, elastic bands and a ruler. Here are some possible containers. You'll see as we go on that I actually used an empty margarine tub.
You need to make a catapult around the legs of a chair using the elastic bands.
One elastic band wasn't long enough so I had to loop three together. Poke one through another elastic band and pull it tight back through itself as shown below.
Here's my band of three.
I put my lightest tin of food into the tub and pulled it back as far as it would go. The red tin at the back was used to mark how far I pulled it back because to make it a fair test we need it to be the same each time. The elastic band provides a force and it is important for Newton's Laws that the force is a control variable (the same each time)
I let go and the tub slid forward. Notice that I had to wedge the single tin with a glove to stop it moving around and dissipating energy when it was sliding. I measured how far it slid from my marker tin to the back of the margarine tub.
I then doubled the mass by using two tins.
I used different combinations of tins to get different masses. At each stage I did 3 repeat readings and got the same pattern of results for each repeat, even though the results were not always perfectly identical due to random error. By doing this I can say that my experiment is
REPEATABLE.
You can read the masses from the sides of the tins. My smaller sweetcorn tins were 150 grams and the heavier tins were 400 grams.
I did the whole experiment again on a laminate floor and found that I got better results. The friction force is smaller. We say an experiment is
REPRODUCIBLE if we get the same pattern of results by a different method or by a different person doing the original experiment. I'm going to argue that getting the same pattern on a different surface means the experiment is reproducible because even though the slide distances were different to the carpet, the graph looked the same shape. If you do the experiment and get the same pattern as I got then it will definitely be reproducible.
