What you Need
Three bowls or washing up basins large enough to put your hand in.
Warm water (NOTE - be careful not to make the water too hot!)
Cold water with a few ice cubes in it
Luke warm water
What to do
1 - Fill one bowl with warm water, one with iced water and one with medium water.
2 - Put one hand into the warm water and one in the iced water for one minute.
3 - Take your hands out of the water and put them both into the medium water. How does the water feel?
What may happen
When you put your hands into the medium temperature water, the hand that's been in the cold water feels warmer while the one that was in the warm water feels cold, even though they are both feeling water that is the same temperature.
Why does it happen?
It's because your senses are relative. They don't measure an absolute temperature or an absolute brightness of light; they make their measurements relative to the things around it. In the case of this experiment, the temperature sensors on your hands measure the temperature of the water relative to the temperature of your hand. If the water is warmer than your hand, it feels warm, and if it is colder than your hand, it feels cold.