The pressure law states that for a constant volume of gas in a sealed container the temperature of the gas is directly proportional to its pressure. This can be easily understood by visualising the particles of gas in the container moving with a greater energy when the temperature is increased. This means that they have more collisions with each other and the sides of the container and hence the pressure is increased.
If V is a constant, the P/T will be a constant — Pressure Law
where V= Volume, P= Pressure and T= Temperature.
If we consider a squash ball to be the sealed container of gas, then the pressure of the gas will vary according to the pressure law. We cannot measure the pressure inside a squash ball, so we make the assumption that the bounce of the ball will be directly proportional to the pressure in the ball. By measuring the “hang–time” (the time between the first and the second bounce) we can make a judgement about what is happening to the pressure inside the squash ball.
The microphone on the DrDAQ data logger will be used to measure the hang–time of the squash ball.
- DrDAQ data logger connected to a PC
- A Beaker, tripod, gauze, thermometer and heat mat
- A metre rule
Carrying out the experiment
- Measure out 200 ml of iced water and check that the temperature of it is 0 °C.
- Using tongs, push the squash ball under the water for about 2 minutes.
- Place DrDAQ on the floor and configure it to measure the “sound level” with a sampling rate of 10 ms
- Start recording the sound level. Using the metre rule as a guide, drop the ball (at 0 °C) from a height of 1 m (see figure 1) and save the file.
- Repeat this three times.
- Now using the Bunsen burner tripod and gauze, increase the temperature of the squash ball to 10 °C and repeat the experiment.
- The experiment should now be repeated for temperatures of 20 °C, 30 °C, 40 °C, 50 °C, 60 °C, 70 °C, 80 °C and 90 °C, being careful with the hot water.
Figure 1: shows the set up of the equipment
Analysing the results from DrDAQ
Using the graph feature in the software we can calculate the hang time of the squash ball. Zoom in on the graph (shown in figure 2) to show clearly the peaks of the first and second bounces. Now use the cursor place it over the first peak, the time of the first peak will now be shown on the screen (see figure 2), repeat this for the second peak. By subtracting these two values you have calculated the hang–time. This means that you can then plot a graph of temperature vs the average hang–time.
Figure 2: shows the data from the bouncing ball
- How did the hang-time vary with the temperature of the ball?
- Was this experiment a fair test?
- What would you think would happen at higher or lower temperatures?
- Can you think of a way of modelling the results?
- Do you think that the squash ball had a constant volume throughout the experiment? If not, did the squash ball obey the pressure law?
- There are several different types of squash ball (different manufacturers, and also different “speeds” — this is denoted by the colour of the spot on the ball). Do you think that this would make a difference to your results? If so, how?
- Do you think that you would get the same results with a tennis ball or a football?