Physics Help Forum atwood's machine

 Kinematics and Dynamics Kinematics and Dynamics Physics Help Forum

 Oct 14th 2012, 11:03 PM #1 Junior Member   Join Date: Oct 2012 Posts: 1 atwood's machine How to find out the upward force acting on the axle of a pulley in an atwood's machine with the masses in an acceleration?
 Oct 15th 2012, 01:35 AM #2 Physics Team     Join Date: Jun 2010 Location: Mauritius Posts: 609 It should be the combined masses of the masses. Otherwise, the axle of the pulley would be falling down or going up, right? And the only forces that have the downward directions are caused by the masses. [Assuming that the weight of the pulley itself is negligible] __________________ Jerry (Got my results!) It is easier to protect your feet with slippers than to cover the earth with carpet. No one can go back and change a bad beginning; but anyone can start now and create a successful ending. If a problem can be solved, no need to worry about it. If it cannot be solved what is the use of worrying?
 Oct 15th 2012, 09:03 AM #3 Senior Member   Join Date: Jun 2010 Location: NC Posts: 419 Atwood's Machine: a Solution Hi, Solution of "g" by use of Atwood's machine is not trivial. If there is an easier solution than mine - I would like to see it. http://www.thermospokenhere.com/wp/0...od/atwood.html Good Luck, Jim
 Oct 15th 2012, 09:57 AM #4 Physics Team     Join Date: Jun 2010 Location: Morristown, NJ USA Posts: 2,354 Hello Thermo. Your solution is a pretty complicated way of doing the math. Much simpler is to use Sum of F=ma: (m+dm)g - mg = (2m + dm)a which yields: g = a(2m+dm)/dm To the OP: the force exerted on the pulley is equal to twice the tension in the rope. If the two masses are m1 and m2, then the acceleration of the system is a=g(m2-m1)/(m2+m1). The tension in the rope is equal to the force required to accelerate the masses, which is the mass's weight plus or minus a force to accelerate them - be careful of signs! Last edited by ChipB; Oct 15th 2012 at 12:38 PM.

 Tags atwood, machine