What Forces Act on a Ball Attached to a Massless Rod in a Vertical Loop?

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Homework Help Overview

The problem involves a ball of mass m attached to a massless rod, moving in a vertical circle with a radius R. The original poster seeks to understand the forces acting on the ball at the top of the loop, particularly questioning whether the massless rod can exert a normal force and how this relates to gravitational and tension forces.

Discussion Character

  • Exploratory, Assumption checking

Approaches and Questions Raised

  • Participants discuss the nature of the forces exerted by the rod, including whether it can exert a normal force despite being massless. They explore the roles of gravitational force and tension at different points in the vertical loop.

Discussion Status

The discussion is ongoing, with participants examining the conditions under which the rod can exert forces on the ball. There is a focus on the relationship between speed and the type of force (pushing or pulling) at the top and bottom of the loop.

Contextual Notes

Participants are considering the implications of the rod being massless and the effects of speed on the forces involved in maintaining circular motion.

bd2015
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Homework Statement



A ball of mass m is attached to a massless rod and is suspended from a frictionless pivot. It is moving in a vertical circle or Radius R such that it has speed v1 at the bottom. The ball is in a vacuum. Find an expression for the force exerted by the rod at the top of the loop as a function of m, v1, g, and R. This is more of a general question. Not looking for an answer to the entire problem. I'm just wondering if the rod exerts a normal force if it is massless. If so, at the top there is a Normal force acting upward and gravity and tension acting downward, correct?
 
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As the mass is attached to the rod, the rod can either push or pull the ball, but there is only one force it exerts on the ball. This force and the weight of the ball keeps it moving along the vertical circle.

ehild
 
ehild said:
As the mass is attached to the rod, the rod can either push or pull the ball, but there is only one force it exerts on the ball. This force and the weight of the ball keeps it moving along the vertical circle.

ehild

So at the top, we have a normal force pushing the ball up, and at the bottom, a tension force pulling the ball?
 
At the top you can have both a pushing force or a pulling one, it depends on the speed which determines the centripetal force needed.

At the bottom, the rod pulls the ball upward.

ehild
 

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