Naked Science Forum

General Science => General Science => Topic started by: neilep on 30/09/2007 18:36:15

Title: My Arm is Under Pressure.....but it will RISE to the occasion !!........why ?
Post by: neilep on 30/09/2007 18:36:15

See this arm  ?

 [ Invalid Attachment ]

Nice isn't it ?


If I apply enough pressure against the wall for a minute or so....why does my arm then want to float upwards ?

What's that all about ?

Thank ewe for your ARMsers !!

Title: My Arm is Under Pressure.....but it will RISE to the occasion !!........why ?
Post by: paul.fr on 30/09/2007 19:59:59

did i not post this in the what's your section, possibly not. i did mean to...neil if i answer will you post the "experiment" over there?

assuming you will say yes, here goes

When an electrical signal from a nerve cell arrives at a muscle, it 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 triggers the contraction of the muscle. When the nervous signal has passed, the sarcoplasmic reticulum reclaims the calcium ions and allows the muscle to relax.

In the case of 'Arm Levitation', usually 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.

Meanwhile a stream of electrical signals arrives at the nerve endings in these muscles, causing lots of calcium to be released into the muscle cells. This prolonged activation doesn't allow the calcium ions to be completely cleared back into the sarcoplasmic reticulum.

When you move away from the wall, there is still a high enough concentration of calcium ions in your muscles to trigger contraction. So even though the command from your nerves has stopped, your arm will lift itself away from your side!

Have you ever tried doing it with your legs? Go on give it a try, just don't wear a skit in mixed company!

Title: My Arm is Under Pressure.....but it will RISE to the occasion !!........why ?
Post by: neilep on 30/09/2007 21:17:35

WOW !!

Excellent answer Paul...I will now copy and paste my original post but change it into question form and place it in that wonderful thread !!

THANKS for the answer....great explanation !!!..does it work with  *cough cough* ' other ' things against a wall ?........... [;)]

Title: My Arm is Under Pressure.....but it will RISE to the occasion !!........why ?
Post by: paul.fr on 30/09/2007 21:53:32

i tried that also, no luck :-(

Title: My Arm is Under Pressure.....but it will RISE to the occasion !!........why ?
Post by: Karen W. on 08/10/2007 15:53:47

How come my arm won't rise like that?

Title: My Arm is Under Pressure.....but it will RISE to the occasion !!........why ?
Post by: Alandriel on 08/10/2007 19:09:25

You need to push quite hard Karen  [:)]

Gosh - we used to do this sort of stuff in primary school  [;D]

Great to see you're not grown up yet!