Interactive Primary Bulletin 38
Science is just magic!

Good, good, good ... good vibrations

This trick relies on the property that metals have good thermal conductivity i.e. the heat energy from our skin can be easily transferred to the metal of coins.

Figure 16 - Suitable coins for the thermal conductivity experiment

Lay out four different coins on a table (Figure 16). Ask a volunteer to face the class, select one coin (stressing they should not touch any of the others) and hold it with the palm of a hand against their forehead. Make sure you let the class see you cannot see their choice.

Tell the volunteer to “think very hard about the coin” as the vibrations from it “should be transferring into their brain”. You should be seen to the class to be concentrating very hard to try and pick up clues about the coin. It is important, for this to work, that the coin spends as much time as possible against the volunteer’s skin. Therefore emphasise that they “should try harder as you are having difficulty reading their mind”. Of course you cannot.

Ask them to lay the coin back down in its place on the table and inform the class, that with your ‘special powers’ you will be able to feel the volunteer’s vibrations from the coin.

As you pick up and feel each coin in turn, one will be perceptibly warmer i.e. the one that had skin contact with the volunteer. See if the children can work out how you do it.

A bird in the hand