
#1
Sep1612, 05:59 PM

P: 129

1. The problem statement, all variables and given/known data
A stick is connected to other partrs of a static system by hinges at its ends. Show that a massless stick feels forces, at the hinges, that are directed along the stick. Then show if the stick is massive, the forces do not need to point along the stick. 2. Relevant equations 3. The attempt at a solution I have no idea where to start or how I can write this out to prove it in every situation. For instance its obvious the the stick attached to a wall and then a block, with a force point away from the wall, that all the forces go with the stick (exactly like tension in a massless rope). Then when mass is introduced the force of gravity clearly offsets the forces felt. I can use the later for the second part, but how does one go about showing the first part in all situations? 



#2
Sep1612, 08:43 PM

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P: 10,925

The key is that the system, including the stick, is static  i.e. the stick does not move.
So, draw a stick in space, and draw a couple of random force vectors at each end. What do the forces have to do for the stick to not move? It's not allowed to rotate or translate. If the forces don't point directly down the stick, how can they balance? 


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