Materials
• Rectangular tank with a divider
• Stopwatch
• Food colouring or other
appropriate dye
• Two containers: one with fresh
water and the other with dyed
salt water (approximately 75g salt
dissolved in 1 l tap water)
• Wave paddle (a wide piece of
plastic about 2 cm high, with a
width similar to that of the tank)
• Optional: a piece of plastic the
same width as the tank but about
one-third of its length