- #1
- 256
- 18
Homework Statement
Someone takes a rock and ties it to a string, and then starts swinging the rock around in a vertical circle.
The centripetal force should be...
Fc = Fg + FtIt's clear that the book sets Ft=0... but why? Can someone explain this?
Homework Equations
Fc = m * ac
ac = v^2/r
The Attempt at a Solution
But, the book says this is wrong. It implies the centripetal force is Fc = Fg at this point. This is very confusing for me. Can someone explain this? Both forces are pointing towards the middle of the circle, but why do we assume that tension isn't there?
If I use Fc = Fg, I get the same answers the book has.
If I use Fc = Fg + Ft, I get an answer that's off by the amount of tension in the string.
Fc is the net force acting in this direction, which at the top of the swing should be gravity and tension. All of the questions in my Ryerson Physics 12 book which want me to calculate something where the object is at the top of the circle set Ft = 0