MadSci Network: Physics

Subject: Question about free fall versus rotating bodies.

Date: Fri Sep 15 10:24:09 2000
Posted by Chris
Grade level: undergrad School: Southampton University
City: Southampton State/Province: No state entered. Country: England
Area of science: Physics
ID: 969027849.Ph

Consider the forces on a metal bar held at each end by some sort of 
support.  On it is a mass, placed anywhere but the centre.

The physics says that the two supports will have different forces applied 
to them by the block (through the effects of gravity), and that when 
released, the block will fall and accelerate under gravity, the bar and 
mass remaining in the former horizontal position.

However, if you imagine this mass to be replaced by some other force, say 
a charged particale is strapped to the bar, and an electic field applied 
to pull the charge (which is near massless!) downwards.....then you can 
see that the situation is the same as before in that different forces are 
to be found at the supports, but now when you realease the bar (and 
charge), surely it will rotate?!

If this is so, then the forces on the supports cannot just be in the 
vertical direction, otherwise the bar, when released, will not rotate (as 
the forces on the supports are different, but now there is no mass to be 

Could you please explain either the flaw in my logic, or the missing 

Many thanks,


Re: Question about free fall versus rotating bodies.

Current Queue | Current Queue for Physics | Physics archives

Try the links in the MadSci Library for more information on Physics.

MadSci Home | Information | Search | Random Knowledge Generator | MadSci Archives | Mad Library | MAD Labs | MAD FAQs | Ask a ? | Join Us! | Help Support MadSci

MadSci Network,
© 1995-2000. All rights reserved.