# During this coursework practical, we aim to study the behaviour of water waves at various depths of water.

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Introduction

Jakub Figurski 5A

GCSE PHYSICS COURSEWORK

1. PLANNING

AIM

During this coursework practical, we aim to study the behaviour of water waves at various depths of water.

METHOD

Firstly, a plastic tank is obtained and its length is measured and recorded. 0.5cm depth of water is poured into it; this depth is measured using a wooden metre rule, vertically positioned resting on the bottom of the tank. One end of the tank is lifted up and is then dropped. This causes a ripple (wave) of water travelling across the water surface to be seen. The time taken for the ripple to get from one end of the tank to the other is timed using an electronic stopwatch (i.e. from one ‘bounce’ to the next). This is repeated twice more for the 0.5cm depth of water. Then the whole process is repeated with different depths: 1.0cm, 2.0cm, 2.5cm, 3.0cm and 4.0cm, again all tested thrice each. Averages of the results collected are taken to level out any anomalies, the results are analysed to investigate the behaviour of water waves at various depths of water, and the speed is calculated for each water depth (speed = distance ÷ time).

DIAGRAM

PRELIMINARY WORK

Before the real coursework experiment, some preliminary investigations were conducted.

Middle

1.38

2.76

5.24

10.54

Average = 1.38

Average = 2.77

Average = 5.23

Average = 10.48

This set of results successfully confirms that the water wave does travel at a constant speed, because the distance of the tank clearly stays the same throughout, and the time taken for the wave to travel this certain distance stays constant (as, for example, the time taken for one ripple bounce is equal to half the time taken for two ripple bounces) so therefore the speed (which is distance ÷ time) must also stay steady. So the distance-time graph representing these results would be a straight line passing through the origin (see below), thus indicating steady speed. This preliminary work also proves that the height from which the tank is dropped does not matter, because the speed of the water wave is the same anyway. Here is a sketch graph of the speed obtained for the preliminary work results:

PREDICTION

My prediction is that as the quantity (depth) of water increases, the waves will travel more quickly, until about 2.5cm, when the best-fit lines begin to go into a plateau. The reasons for this are explained below, in ‘Scientific Knowledge’.

I expect the graph of time and water depth to be plotted like so:

Conclusion

But for the experiment to be fair and successful, there are a number of key factors:

- using the same plastic tank for each test, so that the distance the water wave has to travel for one ‘bounce’ is always exactly the same;

- keeping one’s eye position constant during each test (otherwise one would observe the waves bouncing off from a different angle of eyesight, so the reaction time for the wave bouncing would be different for each bounce, making the results slightly wrong);
- measuring each water depth carefully with a rule from the same point each time, i.e. with the bottom end of the rule resting on the bottom of the tank (see ‘Diagram’, pg. 1);
- ensuring that the forefront of the ripple touching the sides of the tank was used for the starting and stopping of the stopwatch every time, and therefore the experiment was kept fair and the results were more accurate.

This student written piece of work is one of many that can be found in our GCSE Waves section.

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