Touch illusions

Senses

Try this series of illusions all based on touch.

Instructions:

Hot and cold

  1. Take 3 glasses and fill with water
  2. Put one in the fridge, fill the other with warm water from the hot tap (just warm NOT hot water) and fill the third with normal cold tap water.
  3. Put the three glasses in a row in the order: warm, normal and cold.
  4. Pop a finger into the warm water and, with your other hand, pop a finger in the fridge-cold water. Leave for a minute then put both fingers into the middle glass.

Science:

You will feel that the finger that was in the warm water feels cold and the finger originally in the fridge-cold water now feels warm, even though they are both now in the same temperature water. What's happened here is that when your finger was, say, in the warm water it adapted to that temperature. Your body is really only interested in things that change in the environment, as it is the changes that you need to be able to react to. So, after your finger has adapted to the warm water when it goes into the middle glass it's 'expecting' it to be warm. When it's not your brain reasons, "this isn't warm so it must be cold". Similarly, the finger in the fridge water adapts to coldness, and when it moves into the centre glass, that's not cold so it must be hot. So one finger is saying hot the other is saying cold and both are actually at the same temperature.

Instructions:

Archimedes illusion

  1. Cross your index and middle fingers
  2. Roll a marble between your two fingertips (bit fiddly)

Science:

It will feel as though there are two marbles

You will need:

  • Sandpaper of various grades
  • A base board
  • Glue
  • A small ball or spherical object
  • Glasses of water
  • Ear plugs

Instructions:

Rough or smooth

  1. Cut 3 pieces of sandpaper of difference grades into squares.
  2. Stick them onto a base board in the order finest, medium, roughest.
  3. Rub one hand on the fine sandpaper and at the same time rub the other on the rough sandpaper.
  4. After a minute take both hands and rub the medium sandpaper.

Science:

It feels different to each hand. Why? Because the hand rubbing the fine sandpaper first adapts to feeling fine roughness, whereas the hand on the course sandpaper adapts to lots of roughness. So like the temperature illusion when your two hands have had their touch sensors adapted to different roughness, the medium paper will feel different to each.

Instructions:

Floating hands

  1. Let your hands hand down at your sides and grab your trousers/skirt
  2. Pull hard outwards as if you are raising your hands to your shoulders.
  3. Hold the position for a minute, then stop and let your hands hang freely.

Science:

You will feel a mysterious force lifting your arms - you may even find your hands rise all by themselves