# Circular Motion question, why does Fnet = 0 (so that T=W)?

• sodnaz
In summary, the question involves a 0.50kg puck on a level air table connected by a light thread to a 3.0 kg hanging mass. The stable orbit of the puck is achieved when it moves in a circular path of radius 0.15 metres around the hole. The homework equations include the centripetal force equation and the velocity equation. The solution involves finding the tension in the thread and the radial acceleration of the puck. The centripetal force is found to be zero because of the force balance equations on the 3 kg hanging mass and the 0.5 kg puck.
sodnaz

## Homework Statement

A 0.50kg puck rests on a level air table and is connected by a light thread passing through a hole in the table to support a hanging mass of 3.0 kg. A stable orbit is achieved when the puck is sent into a circular path of radius 0.15 metres around the hole.
(A) neglecting friction at the edge of the hole, calculate the period of revolution of the puck in its orbit.

## Homework Equations

Centripetal force = Tension - Weight
V=2πr/T

## The Attempt at a Solution

I know that at that position, F = T-W

I saw this solution online:

However, I don't get why Fnet (centripetal force) = 0 in this instance? If the puck is in it's orbit, how can the centripetal force be 0? Can you explain that please? I just don't understand why the centripetal force is 0?

Thanks

Have you drawn a free body diagram on the hanging 3 kg mass? If so, what is the force balance equation on this mass? What is the tension in the thread?

Have you drawn a free body diagram on the on the 0.5 kg mass? If so, what is the force balance equation on this mass? What is the radial acceleration of this mass?

## 1. What is circular motion and how does it relate to Newton's laws of motion?

Circular motion is the movement of an object along a circular path. It is related to Newton's laws of motion because it involves the application of these laws to objects moving in a circular path.

## 2. Why is Fnet (net force) equal to zero in circular motion?

Fnet is equal to zero in circular motion because the object is moving in a constant speed and direction, meaning there is no acceleration. According to Newton's first law of motion, an object will continue to move at a constant velocity unless acted upon by an unbalanced force. In circular motion, the centripetal force acting towards the center of the circle is balanced by the centrifugal force, resulting in a net force of zero.

## 3. How does the tension in a string or rope cause an object to move in a circular path?

The tension in a string or rope provides the centripetal force that keeps an object moving in a circular path. As the object moves, the string or rope pulls on it, directing it towards the center of the circle. This force, known as the centripetal force, is what allows the object to continuously change direction and remain in circular motion.

## 4. What is the relationship between tension, weight, and centripetal force in circular motion?

In circular motion, the tension in the string or rope is equal to the centripetal force, which is also equal to the weight of the object. This can be shown mathematically through the equation T = m(v^2/r), where T is tension, m is mass, v is velocity, and r is the radius of the circle. This equation illustrates that the centripetal force is directly proportional to the tension and the mass of the object, and inversely proportional to the radius of the circle.

## 5. Why is it important to understand circular motion and its relationship to forces?

Understanding circular motion and its relationship to forces is important in many fields of science and engineering, such as in the design of amusement park rides, satellites, and vehicles. It also helps us understand the motion of celestial bodies, such as planets orbiting around the sun. Additionally, understanding circular motion can help us better understand and apply Newton's laws of motion, which are fundamental principles in physics.

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