For this experiment you need a rectangular box about 30 cm long that won't leak if you put 0.5 cm depth of water in the bottom. I had a look round and found these. they include a rectangular washing up bowl (a round one won't work), a rectangular tray, a storage box, a biscuit tin (even the lid would work) and a cake tub.
However, I chose to use a baking tray. First job is to measure the length of the long side on the INSIDE of the tray. It was 33.9 cm long.
I chose to write it in cm because the ruler is marked in cm. (Proper scientists might prefer 339 mm) But notice that I wrote it in cm to 1 decimal place. This is because although there are numbered cm marks on my ruler, there are 10 marks between each cm. These marks are the SCALE DIVISIONS on the ruler. The smallest scale division is worth 0.1 cm here. We call it the RESOLUTION of the ruler - the smallest reading it could possibly take.
Next job is to fill the tray with water to a depth of about 0.5 cm. I used a jug rather than a tap because I found it easier to control the pouring.
Then tilt the tray at one end to a height of about one finger width off the ground. If you only put in 0.5 depth of water, it shouldn't spill!
Then take your finger out so that the tray drops suddenly. Notice that I did the experiment in the kitchen - I was worried about spilling!
The water sloshes back to cover the empty bit at the raised end. See below. When it hits the end at A it makes a wave. Start timing when the water hits end A.
The wave will look like a ripple heading along. Stop timing when it hits end B. It took just over 1 second for mine.
Do A to B three times so that you can calculate a mean. Then do A to B to A. It is twice as far so we should expect it to take twice as long if it is PROPORTIONAL.
You need to keep going until you have timed the waves doing FIVE lengths of the tray if you can. It was hard to see the ripple for the fifth length because so much energy was dissipated but it was tehre if I looked carefully. Here is the start of my results table.
When you take repeat readings, you get a RANGE of results.
RANGE means (biggest repeat reading - smallest repeat reading). I have circled the three repeat readings. The biggest is 1.31 seconds and the smallest is 1.28 seconds. So here range = 1.31 - 1.28 = 0.03 seconds.
If you get asked for UNCERTAINTY for your repeat readings,
UNCERTAINTY means HALF THE RANGE. Here that means 1/2 x 0.03 = 0.015 seconds.
