# Tagged Questions

A tag for questions about the mechanical interactions of rotating objects, including torque and angular momentum.

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### Conceptual rolling

If you could roll a ball down a slope with friction, we would all know which direction the ball is rolling. However, say we have a frictionless slope and we roll the ball in the opposite direction and ...
2k views

### Veritasium - Firing bullet in block - along center and away from center

This question is about this video on YouTube, in which a bullet is fired vertically into the center of a wooden block from below, sending the block up into the air. Next, a bullet is fired vertically ...
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### how does international space station change its orientation?

In what way does the rotating gyroscope help in changing the orientation of the international space station in space ? Is there any other way to change the the orientation of ISS ?
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### Factors affecting torque and RPM of a motor [closed]

I am not a physics guy, so not even the basic concept of a DC motor is easy for me. My question is as follows: How do these parts of a motor affect its RPM and Torque? I had my research a while ago ...
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### Astronaut on a rotating asteroid

This might sound like the silliest question ever, but can someone shed some light on what is actually happening in the following situation: There is an asteroid in outer space what is rotating with ...
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### Can moment of inertia be negative? [closed]

Q: Find out the moment of inertia of a uniform circular disc of radius $r$ & mass $M$ & the axis passes through a point on the circumference. My attempt: Let the axis passes through $O$ on ...
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### Why doesn't static friction decelerate a rolling body?

I know that static friction isn't the cause of deceleration of a rolling body. But if static friction is the only force in the horizontal direction, then shouldn't there be some acceleration produced ...
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### Why does dust stick so well to fan blades? [duplicate]

After reading and understanding the reasons why dust stick to rotating fan propeller, I am interested to find out why the dust particles stick so well. Spraying powerful jets of water does not ...
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### Ice skater increase of energy

This may be a very basic question but I am not seeing how it works. Consider the standard example of an ice skate rotating about his/her center of mass and pulling in his/her arms. The torque is zero ...
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### Friction-free rolling/sliding on an inclined plane

Suppose a sphere is rolling down an inclined plane. There is no friction. The body will not roll and undergo just a translation. But why is this so? If we consider the axis to be along the point of ...
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### Why do tires with low air pressure experience more friction?

How does tyre pressure affect the frictional force on a tyre even though friction is independent of area of contact? And how does one analyze or calculate this friction?
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### Why does the water bottle not rotate when it is half full?

Consider this water bottle: When it is full and thrown up in the air, it rotates at a constant velocity. When it is less than 1/8th full, the water bottle rotates even faster than when it was full....
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### Rolling as pure rotation

In my book the following statement was written and I didn't understand it well. Can anyone explain it in a more simple way? Figure 11-6 suggests another way to look at the rolling motion of a ...
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### Intuitive explanation for why same force applied farther from a hinge causes larger angular acceleration than if applied closer?

A standard example of a problem involving torque is opening a door - the same force F applied far from the hinge causes a larger angular acceleration than if applied close to the hinge. I always had ...
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### Calculating the path of a ball with spin moving across a table

A ping pong ball is rolling over a smooth (but not frictionless) table. During its travel, a clockwise spin is placed on the ball. The ball's path is changed to move to the right (in perspective from ...
533 views

### Foucault pendulum

The equations of motions for a Foucault pendulum are given by: $$\ddot{x} = 2\omega \sin\lambda \dot{y} - \frac{g}{L}x,$$ $$\ddot{y} = -2\omega \sin\lambda \dot{x} - \frac{g}{L}y.$$ What are the ...
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### What causes precession or nutation in a spinning object?

What causes precession in a spinning object? What causes nutation in a spinning object? What causes a top, gyroscope, and the earth to wobble? Just because it's a simple question, I'm not ...
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### Meaning of angular velocity in a rotating system

When you study the motion of a rigid body you have $\vec\omega$, the vector associated to angular velocity. In the case you are using Euler angles and want a quick formula for the rotational kinetic ...
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### Altering Venus rotational speed to match Earth's via weather manipulation

Venus rotates approximately 6.5 km an hour Earth rotates approximately 1650 km/h how fast could we speed up Venus's rotation via only weather manipulation ( maybe a giant fractal lens between Venus ...
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### What “I” should use in Rotational Energy formula $(I \omega^2)/2$

$\text{Rotational Energy} = \frac{1}{2} I \omega^2$. What $I$ should be used? $I$ as a inertia tensor matrix = stepRotation * inverse moment of inertia * inverse stepRotation; Or I as moment of ...
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### What is the direction of the friction force on a rolling ball?

Suppose you have a solid ball on a horizontal table. What is the direction of friction force when the ball I pushed horizontally and starts rolling? Why is the direction of friction as it is? Which ...
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### Differential equation of motion of combined rigid body

I am reading the following paper: http://tinyurl.com/jv2pu2m I have a question about (1) and (2): To (1), I think the following link provides good explanation. Equation of Motion for Rigid ...
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### Intuitive explanation of rotational inertia with respect to angular momentum

I understand that there are proofs (e.g. proof, another proof) of why the angular momentum about two points for an object is the same. However, could someone give an intuitive explanation of why this ...
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### What makes us twist in a somersault?

In a backwards straight somersault you can decide whether you twist early or late. Twisting early means, that you induce the twisting movement before you rotatation hits 180° and twisting late means, ...
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A deadblow hammer is a type of mallet with a hollow head filled with shot or sand. When you hit with it, say on an anvil, the mallet does not rebound, but just falls flat and heavy. I don't ...
I have read that $$\vec\tau=\frac{\mathrm{d}\vec L}{\mathrm{d}t}$$ holds true whenever the origin is not accelerating. But I cannot see why this holds true for a rotating frame of reference (such as ...