# Tag Info

Accepted

### Why can we treat a ball as a point mass to calculate torque?

Calculating the torque on a rigid body w.r.t to the point $\vec 0$ (WLOG) with gravity pointing in a constant direction $\hat n$ is accomplished by integrating over the rigid body, with each ...
• 3,878

### Does a rocket moving in a circle expel exhaust at a greater velocity?

This is an interesting question, because when it is moving in a circle, the magnitude of its tangential velocity is constant and its angular velocity is also constant. Therefore the total kinetic ...
• 5,851

### Does a rocket moving in a circle expel exhaust at a greater velocity?

The energy of the fuel does become the kinetic energy of the exhaust. Let us ignore the fact that the rocket becomes lighter as it burns fuel, and that it will eventually run out of fuel. The rocket ...
• 41.1k
Accepted

### Why doesn't centrifugal force change instantly?

This behavior is not caused by centrifugal force, but rather by conservation of angular momentum. If you take any spinning object, and draw an arrow aligned with the axis of rotation, that arrow ...
• 9,463

### Why does moment of inertia stop at 1/2 as solidness of a cylinder increases?

The reason that the moment of inertia gets smaller as the annulus gets less like a hoop and more like a disc is that more of the mass is closer to the axis of rotation. You can make the moment of ...
• 91.4k

### Why can we treat a ball as a point mass to calculate torque?

The torques can be calculated in respect to any point, and it generally requires taking integrals. However, there are some basic tricks to simplify life. One of them is choosing the rotation axis at ...
• 60.1k

### Is angular velocity about any point in a rigid body always the same?

Doubt 1 It is measured about the axis of rotation. Doubt 2 Yes. For a rigid body all points will complete one revolution, $2\pi$ radians, about any axis of rotation in exactly the same amount of ...
• 73.6k
Accepted

### Spinning a rope conundrum

You are exciting standing "circularly polarized" waves in the rope. If you continue to spin at a faster frequency, you can create even more "nodes" in the rope (stable points of ...
• 978

### Is it possible to reproduce tennis racket theorem instability with a gymbal under earth gravitational field?

I'm posting a new answer for the following reason: a totally different way of implementing a Dzhanibekov effect demonstration occurred to me. Manufacture an object that is spherical on the outside, ...
• 21.4k

### Is it possible to reproduce tennis racket theorem instability with a gymbal under earth gravitational field?

A gimbal suspension for the purpose of demonstrating the Dzhanibekov effect (when weightlessness is not available) presents special challenges. In a comment I already linked to the video about the ...
• 21.4k