Uncertainity regarding measurement

[shounakbhatta]

Hello,

I was viewing a lecture of one of the professor's most possibly in MIT who demonstrated in the class room, by calling a boy and measuring him, while standing, a certain measurement say 5 ft. After that he asked the boy to lie down and again measured him and found that there is a difference, say +- some amount. He concluded that there is always a uncertainty in measurement while standing and the same person lying down.

Can anybody please explain me the reason? Why?

Thanks.

 

[SteamKing]

What changes occur to the boy standing versus laying down?

 

[shounakbhatta]

Nothing physically. The measurement rod shows the difference. Can you tell me the reason please?