OK I was talking to my Mum just now about the old 'Levitation party trick' where 4 people lift a person up high using their fingers. You know the one.
Anyway I told her how it is just a case of the weight being distributed over 4 people and them being in a position which gives them good leverage (as explained in Flim Flam!) but she's not buying it. Reason is as follows, and my science is not good enough to argue my case:
She says that the person she liftes was about 12 stone and that she doesn't believe she could lift 3 stone with just her fingers. She performed a variation of it where, instead of just reciting some chant, the 4 people actually pushed down on the persons head and shoulders beforehand. Due to Newton's 3rd law the body of course exerts a reaction force. But she believes the body continues to exert this force after the people have stopped pushing, and this is what made the person feel 'as light as a feather, not 3 stone'
Another example of this effect (she claims) is when you stand in a doorway and push against one side with your arm for about a minute. When you stand away your arm magically rises! Now I admit this is a very cool trick, but I asserted that it was to do with the brain being fooled and continuing to stimulate the shoulder muscle to raise the arm, not that the force she was exerting somehow lingering on even after she had stopped consciously pushing.
Anyway can someone provide a good scientific explanation of the 2 things I have mentioned here as I am running out of ideas! It is particularly hard to explain why the person she 'levitated' feeling literally weightless rather than 3 stones worth. I could just say it was in your head, you were psyched up and didn't really notice the weight, but of course a believer isn't going to accept that!
Anyway I told her how it is just a case of the weight being distributed over 4 people and them being in a position which gives them good leverage (as explained in Flim Flam!) but she's not buying it. Reason is as follows, and my science is not good enough to argue my case:
She says that the person she liftes was about 12 stone and that she doesn't believe she could lift 3 stone with just her fingers. She performed a variation of it where, instead of just reciting some chant, the 4 people actually pushed down on the persons head and shoulders beforehand. Due to Newton's 3rd law the body of course exerts a reaction force. But she believes the body continues to exert this force after the people have stopped pushing, and this is what made the person feel 'as light as a feather, not 3 stone'
Another example of this effect (she claims) is when you stand in a doorway and push against one side with your arm for about a minute. When you stand away your arm magically rises! Now I admit this is a very cool trick, but I asserted that it was to do with the brain being fooled and continuing to stimulate the shoulder muscle to raise the arm, not that the force she was exerting somehow lingering on even after she had stopped consciously pushing.
Anyway can someone provide a good scientific explanation of the 2 things I have mentioned here as I am running out of ideas! It is particularly hard to explain why the person she 'levitated' feeling literally weightless rather than 3 stones worth. I could just say it was in your head, you were psyched up and didn't really notice the weight, but of course a believer isn't going to accept that!
).
