Mark Cramoysan, Head of Physics, Leeds Grammar School: This is one for Sixth Form physics students. Set the machine up so that students row for 30 seconds at a time and the display is set to power in watts. Have the first student row at a power of about 50W. At the end of the time, the average power can be read and, if the display is swapped to distance, you can read the distance covered. Work out the speed by dividing distance by time (30 seconds). Repeat with the next student rowing at about 100W. Continue until the students are exhausted, making sure that the biggest, burliest student comes last. A graph of power required versus speed is an upwards curve. If you plot Power versus speed cubed, you get a straight line, as the laws of physics would suggest. Of course, it is all a con, since the machine 'knows' about the laws of physics, but the results are rather satisfying.