It is possible to see an alarm clock ring as well as to hear it. When you are standing close to the alarm clock, it seems quite loud. As you move away from the clock, the alarm sounds quieter, so our distance from the source of a sound will affect how loud it seems.

First broadcast:
15 October 2007

After viewing the clip, ask the children to sit at one end of the classroom. Put a loudly ticking clock at the opposite end. Measure the distance between children and the clock, using a tape measure. Then place the clock a metre closer and then another metre closer, until the clock is as close as it can get. Ask the children to note how loud the clock sounds in each position. Blindfold a child and ask him or her to guess the distance of the clock, just from hearing its ticking. Are some children more accurate guessers than others? Ask children to cup their ears with a hand - does it make the ticking easier to hear? Can anyone suggest another way to make the ticking clock sound quieter (for example, by muffling it)?