Levitation

You will need:

* A number of people (more than one for best effect)
* A narrow doorway

What to do:

Stand in the narrow doorway with your arms at your sides. Lift your arms up slightly so that you're touching the doorframe on either side with the backs of your hand


Now exert some effort! Press the back of each hand into the doorframe as hard as you can for 40 seconds.


Keep pushing…


Step away from the doorway and relax. What happens? Your arms will magically begin to levitate with no effort from you.


Get your group of friends to do the same thing and you can all stand around with your arms hanging in the air!

NB. The effect only lasts for a short time, so don't worry, you won't need to walk around like a penguin forever.

What's happening?

When you want a muscle to contract, your body sends an electrical signal along a nerve cell from the brain to the muscle. The signal starts a series of events that result in the contraction of that muscle.

The main event is the release of calcium ions into the muscle cells from the muscle's calcium store, or 'sarcoplasmic reticulum'. This increase in calcium makes the muscle contract.

When the nervous signal stops, the calcium ions go back into the sarcoplasmic reticulum and the muscle can relax.

To lift your arm from your side you use two muscles in your shoulder, the deltoid and supraspinatus muscles. By pressing your arm against the doorway you are sending a command to these muscles to move, but they can't because the doorframe's in the way.

As you carry on pushing against the doorway, you are still telling your muscles to move. A stream of electrical signals arrives at the nerve endings in these muscles. Masses of calcium ions are released into the muscle cells and they can't be completely cleared back into the sarcoplasmic reticulum.

When you move away from the wall, there is so much calcium in your muscles and they can finally contract in response! So even though the command from your nerves has stopped, your arm will lift itself away from your side!