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11 votes
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 ...
jwimberley's user avatar
  • 3,888
3 votes

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 ...
Roger V.'s user avatar
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1 vote

Confusions in conservation of angular momentum and torque

Oh, I get it. The equation $\tau_z = I\alpha_z$ is not valid for a non-rigid object (even if it is solid and doesn't change forms, if it changes in radius relative to the axis, it is non rigid, as ...
Jinsu Jang's user avatar
1 vote
Accepted

Buoyant force on a stick making an angle theta with the vessel

Divide the underwater world into two parts - the water and the stick. Suppose the water disappeared, leaving the stick. The force on the stick would be the weight of the stick. Suppose you replaced ...
mmesser314's user avatar
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1 vote
Accepted

Forces accelerating a tire

I suggest a simple model to cover the no slipping and the slipping situation. Why don't the green and blue arrows simply cancel out, resulting in no acceleration/motion? Because the forces act on ...
Farcher's user avatar
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