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

In summary, the conversation discusses a ball of mass m attached to a massless rod moving in a vertical circle of radius R with speed v1 at the bottom. The force exerted by the rod at the top of the loop is expressed as a function of m, v1, g, and R. It is also clarified that the rod can either push or pull the ball, but there is only one force acting on it which keeps it moving along the circle. At the top, there can be a normal force pushing the ball up or a pulling force depending on the speed, while at the bottom the rod pulls the ball upward.
  • #1
bd2015
8
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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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  • #2
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
 
  • #3
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?
 
  • #4
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
 
  • #5


Yes, you are correct. The massless rod will still exert a normal force on the ball at the top of the loop. This is because the normal force is a reaction force to the weight of the ball, which is acting downwards due to gravity. At the top of the loop, the weight of the ball is still acting downwards and the normal force is acting upwards to balance it out. In addition, there will also be tension in the rod due to the ball's circular motion, which will also act downwards. So at the top of the loop, the forces acting on the ball will be the normal force, gravity, and tension.
 

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

1. What is a ball on a massless rod?

A ball on a massless rod refers to a physical model used in science to represent a small, spherical object connected to a weightless or massless rod. This model is often used in physics and engineering to simplify calculations and understand the behavior of objects in motion.

2. How does a ball on a massless rod behave?

In theory, a ball on a massless rod would behave as if the rod had no weight at all. This means that the ball would experience no gravitational force from the rod and would move freely without any resistance. However, in reality, all objects have some mass and weight, so the behavior of a ball on a massless rod would depend on the specific conditions and forces acting on it.

3. What is the purpose of using a ball on a massless rod model?

The purpose of using a ball on a massless rod model is to simplify calculations and understand the behavior of objects in motion. By assuming that the rod has no mass, scientists and engineers can focus on other factors such as gravity, friction, and acceleration to better understand the movement and forces acting on the ball.

4. Can a massless rod exist in reality?

No, a massless rod cannot exist in reality. All physical objects have some mass and weight, no matter how small. However, in certain situations, the mass of a rod may be negligible compared to other forces acting on it, allowing scientists to use the concept of a massless rod as a simplifying model.

5. What are some real-life applications of a ball on a massless rod?

A ball on a massless rod is often used in physics and engineering to understand the motion and forces acting on objects such as pendulums, rotating objects, and projectiles. This model can also be applied to real-life situations, such as the movement of satellites in space or the motion of a swing at a playground.

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