# Torque on a spherical planetoid galaxy

• Borat321
In summary, the conversation discussed the spin angular momentum of a spherical planetoid in a galaxy far, far away, and how an external torque is causing its axis of rotation to gradually change direction. The question asked for the rate of change of the planetoid's angular momentum in that direction and the magnitude of the external torque exerted on the planetoid. The answer provided the formulas for calculating these values, using the spin angular momentum and angular velocity.
Borat321
Hi - I had a question on webassign - here is the question.

A spherical planetoid in a galaxy far, far away has spin angular momentum of magnitude L = 5.9e+35 kg m2/s directed out of its north pole. An external torque acts on it, such that the planetoid's axis of rotation, and hence its angular momentum vector, gradually changes direction, describing a cone with half-angle 23.5 degrees as shown in the figure.
Define the y-axis as straight up in the figure (the vertical arrow shown). Define the x-axis as to the right.

Suppose the angular momentum vector takes 21200 years to swing once around the cone shown. What is the magnitude of the rate of change of the planetoid's angular momentum in that direction at the instant shown? (Hint: consider the analogy between how the component of angular momentum changes with time, and how the position of a particle in circular motion changes with time.

What is the magnitude of the external torque exerted on the planetoid?

I thoiught that the rate of cahnge of the planetoid's angular momentum can just be Lsin(23.5)w, where L=5.9e+35 and w = 2pi/21200 converted into seconds.

Also, I thought torque would just be rFsin23.5, where r = radius of Earth, but where am I going wrong?

The rate of change of the planetoid's angular momentum in that direction would be: Lsin(23.5)w, where L is the magnitude of the spin angular momentum (5.9e+35 kg m2/s) and w is the angular velocity (2π/21200). The magnitude of the external torque exerted on the planetoid is: T = Lsin(23.5)w, where L is the magnitude of the spin angular momentum (5.9e+35 kg m2/s) and w is the angular velocity (2π/21200).

I would like to clarify and expand on the concept of torque and angular momentum in this scenario. Torque is a measure of the force that causes an object to rotate around an axis. In the case of the planetoid, the external torque is causing the planetoid's axis of rotation to change direction, thus changing its angular momentum vector.

The rate of change of the planetoid's angular momentum in the direction shown can be calculated using the cross product of the planetoid's angular momentum vector and the external torque vector. This will give us the magnitude and direction of the change in angular momentum.

To calculate the magnitude of the external torque, we need to consider the radius of the planetoid and the force acting on it. The force can be calculated using the formula F=ma, where m is the mass of the planetoid and a is its acceleration. This acceleration is caused by the external torque, so we can use the formula T=Iα (torque= moment of inertia x angular acceleration) to find the torque.

In summary, the rate of change of the planetoid's angular momentum can be calculated using the cross product of its angular momentum vector and the external torque vector. The magnitude of the external torque can be found using the formula T=Iα, where I is the moment of inertia and α is the angular acceleration. These calculations will give us a better understanding of the dynamics of the planetoid's rotation and the effects of external forces on it.

## 1. What is torque on a spherical planetoid galaxy?

Torque on a spherical planetoid galaxy refers to the rotational force exerted on the galaxy due to the distribution of mass and the gravitational pull of neighboring galaxies.

## 2. How is torque calculated on a spherical planetoid galaxy?

Torque on a spherical planetoid galaxy is calculated using the formula τ = r x F, where τ is the torque, r is the distance from the axis of rotation to the point where the force is applied, and F is the force acting on the galaxy.

## 3. What factors affect the torque on a spherical planetoid galaxy?

The torque on a spherical planetoid galaxy is affected by the distribution of mass within the galaxy, the gravitational pull of neighboring galaxies, and the shape of the galaxy itself. Other factors such as collisions with other galaxies and dark matter can also play a role.

## 4. How does torque impact the rotation of a spherical planetoid galaxy?

The torque on a spherical planetoid galaxy causes it to rotate, and can also affect the speed and direction of its rotation. The magnitude and direction of the torque can determine the stability and overall motion of the galaxy.

## 5. Can torque on a spherical planetoid galaxy be measured or observed?

Yes, torque on a spherical planetoid galaxy can be measured and observed through various techniques such as studying the rotation curves of galaxies, analyzing gravitational lensing effects, and using computer simulations to model the dynamics of galaxies.

• Introductory Physics Homework Help
Replies
5
Views
196
• Introductory Physics Homework Help
Replies
4
Views
1K
• Introductory Physics Homework Help
Replies
7
Views
1K
• Introductory Physics Homework Help
Replies
10
Views
953
• Introductory Physics Homework Help
Replies
5
Views
5K
• Classical Physics
Replies
2
Views
916
• Mechanics
Replies
2
Views
1K
• Introductory Physics Homework Help
Replies
12
Views
2K
• Introductory Physics Homework Help
Replies
1
Views
1K
• Introductory Physics Homework Help
Replies
26
Views
3K