# Drawing free body diagrams for pendulum

• vu10758
In summary, the conversation is about drawing and labeling a free body diagram for a pendulum at its maximum amplitude of 30 degrees. The vectors must be correctly scaled and the directions must be correct. The individual discussing the problem has drawn the diagram with T pointing up and to the left, and has also included gravity mg with two components. They reason that mgcos(30) is smaller than T because the pendulum is in motion and the tension and centripetal force are in the same direction. However, there is some confusion about whether the reasoning is correct and whether the criteria for the diagram have been fulfilled.
vu10758

## Homework Statement

I have to do this for a lab. Draw and label the free body diaggram of a pendulum when it is at its maximum amplitude of 30 degrees. The magnitudes of the vectors must be correctly scaled and the directions correct.

## The Attempt at a Solution

I drew the free body diagram with T pointing diagonally up and to the left. The arc angle is 30 degrees. I then draw gravity mg straight down with two components, mgcos(30) and mgsin(30). I reasoned that mgcos(30) is smaller than T in magnitude because the pendulum is in motion. The tension and centripetal force are in the same direction, and the pendulum is not at rest. Is my reasoning correct?

Seems okay from your description, but we aren't going to know whether you fulfilled all the criteria for the free body diagram.

That first statement is confusing. An amplitude of 30 degrees?

Mindscrape said:
Seems okay from your description, but we aren't going to know whether you fulfilled all the criteria for the free body diagram.

That first statement is confusing. An amplitude of 30 degrees?

It means that at most the pendulum travels 30 degrees in either direction from equilibrium point.

vu10758 said:

## Homework Statement

I have to do this for a lab. Draw and label the free body diaggram of a pendulum when it is at its maximum amplitude of 30 degrees. The magnitudes of the vectors must be correctly scaled and the directions correct.

## The Attempt at a Solution

I drew the free body diagram with T pointing diagonally up and to the left. The arc angle is 30 degrees. I then draw gravity mg straight down with two components, mgcos(30) and mgsin(30). I reasoned that mgcos(30) is smaller than T in magnitude because the pendulum is in motion. The tension and centripetal force are in the same direction, and the pendulum is not at rest. Is my reasoning correct?

At 30º the pendulum is momentarily at rest. There is no centripetal acceleration at that point.

## 1. How do you draw a free body diagram for a pendulum?

To draw a free body diagram for a pendulum, you first need to identify all the forces acting on the pendulum. These include the force of gravity, tension in the string, and air resistance. Then, draw a dot or small circle to represent the mass of the pendulum at the end of the string. From the dot, draw arrows representing the direction and magnitude of each force.

## 2. What is the purpose of drawing a free body diagram for a pendulum?

The purpose of drawing a free body diagram for a pendulum is to visually represent all the forces acting on the pendulum. This can help in analyzing the motion of the pendulum and determining the net force acting on it.

## 3. How do you determine the direction of the tension force in a free body diagram for a pendulum?

The tension force in a free body diagram for a pendulum is always directed towards the pivot point of the pendulum. This is because the string or rod that the pendulum is suspended from is always pulling towards the pivot point.

## 4. Is air resistance a significant force in a free body diagram for a pendulum?

It depends on the situation. In most cases, the force of air resistance on a pendulum can be neglected because it is relatively small compared to the other forces acting on the pendulum. However, if the pendulum is swinging at high speeds or in a highly turbulent environment, air resistance may have a noticeable effect on the motion of the pendulum and should be included in the free body diagram.

## 5. Can a free body diagram for a pendulum be used to determine the period of the pendulum?

No, a free body diagram is used to analyze the forces acting on the pendulum, not the motion. The period of a pendulum is determined by its length and the acceleration due to gravity, and can be calculated using the formula T = 2π√(L/g), where T is the period, L is the length of the pendulum, and g is the acceleration due to gravity.

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