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

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3
votes
2answers
171 views

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 ...
0
votes
1answer
23 views

How do I incoporate gyro information in my position and velocity calculation? [closed]

The velocity in 1 direction can be calculated as : $V_t=V_0+at$ And position could be calculated as $P_t=V_0t+1/2at^2$. Besides time, acceleration, I was also given information from 3 axis ...
4
votes
3answers
207 views

What is an intuitive explanation using forces for the equatorial bulge?

The earth is not a sphere, because it bulges at the equator. I tried fiddling with centripetal force equations and gravity, but I couldn't derive why this bulge occurs. Is there (a) a ...
2
votes
1answer
50 views

Cylinder inside a cylinder - moment of inertia

A homogeneous cylinder with radius a and mass m rolls in a hollow cylinder with radius R. Determine the kinetic energy of the cylinder as function of $\dot{\theta}$. I'm sorry for ...
3
votes
2answers
85 views

Advantages of a deadblow hammer?

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 ...
2
votes
0answers
35 views

Autocorrelation function corresponding to density of states with significant rotational motion

Most statistical physics textbooks (at least the ones I've found) state simply that the density of states of a system can be found as the temporal Fourier transform of the velocity autocorrelation ...
1
vote
2answers
76 views

Will increased weight slow a pendulum?

When a pendulum is swinging, if you could instantly add significant weight to the bob without altering it in any other way, will that weight increase drag and cause the pendulum to move to equilibrium ...
0
votes
2answers
51 views

Friction in Rolling Motion [duplicate]

My understanding of rolling motion: When a body rolls, at every instant, there is just one point of contact between the body and the plane and this point has no motion relative to the plane. Now ...
0
votes
1answer
48 views

If I start spinning a raw egg slowly why does its angular velocity increase spontaneously?

If I start spinning a raw egg very slowly in place, why does its angular velocity increase spontaneously? This is something I noticed the other day while cooking. It doesn't do the same thing with a ...
0
votes
2answers
65 views

Converting Pendulum into Electricity? [closed]

I've been thinking about this, I want to use this as my science project. The two viable solutions I've thought of so far are magnet or rotary based. Pendulum clocks could be powered once a day and ...
1
vote
3answers
781 views

Will an object rotate when we apply a force to it?

What would happen if the axis of rotation passes through the centre of mass of an object? Will the object rotate when we will apply a force to the object? Edit: The object is free, is not fixed to an ...
1
vote
3answers
192 views

Uniform Circular Motion and Centripetal Acceleration

In introductory physics books (or at least mine) it limits the equation $a_c=v^2/r$ to the situation where the speed around the circular path is constant. It enforces the idea that the speed is ...
2
votes
2answers
1k views

Force applied off center on an object

Assume there is a rigid body in deep space with mass $m$ and moment of inertia $I$. A force that varies with time, $F(t)$, is applied to the body off-center at a distance $r$ from its center of mass. ...
7
votes
2answers
203 views

Does a rotating disk develop a potential difference between the centre and rim?

This stems from thinking about the question If a perfect conductor where to move what happens to the electrons?. Suppose we have a rotating disk with no external magnetic field, so this is not a ...
0
votes
1answer
37 views

How to calculate friction on a spinning ball on the ground?

If there is a ball on the ground initially at rest, Assume that the plane xoy(cartesian) is the ground and that Z is the normal of the ground. If I spin the ball so that $\omega_x=\omega_y=0$ and ...
18
votes
8answers
3k views

Does it take more energy to open a door when applying force close to the hinge?

Assuming an ordinary hinged door (without any springs), would it take more energy to open it when applying force in the middle of the door (point b), rather than at the end of the door (point a), ...
0
votes
1answer
76 views

What is really the force required to open a door?

I found a few Phys.SE threads in which an impulse is used to exert a torque on a rod, is it possible to get a realistic description of the force required to open a door?: If we have a free 'door' ($l ...
0
votes
1answer
38 views

On application of angular momentum conservation laws

Consider a situation like this: a massless ring is kept fixed at rest on a horizontal plane. A massless thin string attached at its one end to a point on the circumference of the ring while its other ...
0
votes
0answers
24 views

calculate the tile of rotation axis of a rolling ball

I want to solve the problem of friction effect on rotation axis of a rolling ball on collision with another ball. I've read Tennis racket theorem in this wikipedia article and thought it might ...
8
votes
2answers
660 views

Is it possible to produce gravitational waves artificially?

Why don't they make a ball with irregularities, say the size of a tennis ball, then spin it very rapidly, so it would produce gravitational waves like a spinning star with irregularities on it? Is ...
1
vote
2answers
49 views

Torque (in $Nm$) of a cyclist

We're discussing bicycles with a friend, and it came to safety, speed and power. Now the question we have is: how much torque do my legs provide to the bicycle? I'm no expert in physics sadly, and ...
1
vote
1answer
29 views

How far does a ball thrown over a surface with friction slide until it starts rotating? [closed]

A bowling ball is thrown horizontally with initial velocity $v$ and no initial rotation over a surface with static coefficient of friction $\mu$. Determine the distance the ball travels ($d$) until ...
0
votes
2answers
68 views

Why does the ball lose contact if it has velocity great or less than $\sqrt{rg}$, while moving over a smooth sphere of radius $r$?

Let a ball of mass $m$ is given a velocity over the the top of a smooth sphere of radius $r$. The equation of motion at the topmost point will be $$mg - N = m\dfrac{v^2}{r}.$$ As $v$ increases, $N$ ...
0
votes
2answers
79 views

If the velocity of an object, rotating on a vertical circle, at the topmost point is zero, how can it loop the whole circle?

Normally, if a body is attached to a string & is rotated in a vertical circle, then to loop the whole circle, the rope must not slack at the topmost point & there should be a velocity for ...
1
vote
2answers
57 views

How 'rare' is no-slipping?

I have come across a lot of questions that say something like: A ball rolls down a hill without slipping... But I have done the maths and found that a ball would only 'not slip' if the friction ...
0
votes
2answers
284 views

Is work done in rolling friction?

I am confused by rolling friction. Suppose you have a cylinder rolling which starts at rest at the top of an incline plane and begins to roll down the plane without slipping. Is work done by the ...
1
vote
1answer
68 views

Angular acceleration as a function of torque

I know that the angular momentum $\mathbf{L}_{cm}$ with respect to the centre of mass of a rigid body can be expressed as $I\boldsymbol{\omega}$ where $I$ is the inertia matrix and ...
1
vote
1answer
56 views

How do we “cancel out” the torque from running?

Running certainly causes a torque on our body, as we are propelled forward via our feet; why doesn't this torque cause our bodies to spin about their center of mass?
3
votes
2answers
76 views

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 ...
0
votes
1answer
29 views

Spinning Ball in Frictionless Tube

If we have a ball in a frictionless tube, and we begin to spin the tube about one end, the ball will exit the tube, correct? Indeed, there must be some centripetal acceleration, but then what force is ...
36
votes
8answers
8k views

Why doesn't a bike/bicycle fall if going with a high speed?

Why does a bike/bicycle fall when its speed is very low or close to zero and is balanced when going with a high speed?
3
votes
2answers
107 views

How does the kinetic energy of a ballerina increase? [duplicate]

When a ballerina pulls her arms in, her rotational kinetic energy increases because angular momentum is conserved. That means that work must have been done on her. I saw somewhere that there is work ...
0
votes
2answers
76 views

Calculating the Precession

This is the Anti gravity wheel video from Veritassium. I have a similar problem to calculate the forces on arm. How can I calculate the precession force pushing the arm vertically ? Lets assume ...
1
vote
2answers
99 views

In which direction does mud fly off a moving bike's tire & why?

If a bike moves through a muddy area, mud gets on its tires. Then the mud flies off from the tires. Which forces are acting on it? In which direction does it fly off? On my physics test, I wrote ...
0
votes
0answers
28 views

Can you explain in mathematical term of how the moon makes the earth spin stable?

I heard that our moon keeps the earth's rotation at the same angle. This is, as the Science Channel explained, is essential for regular seasons on earth. I am not interesting in the fact why it is ...
15
votes
3answers
2k views

Does holding weights allow you to run faster?

I'm not talking about training with weights so that when you run without them your muscles are used to pushing more weight so with less weight it'll be easier, I'm talking about while actually holding ...
2
votes
2answers
196 views

Angular momentum with respect to the centre of mass

I have been told [Warning: I leave this because it's what I asked and allows to understand the dialogues in the comments, but Azad, whom I thank, has pointed that the formula does not hold in general ...
0
votes
2answers
141 views

When does the 'standard' angular velocity formula not hold?

I have read that the formula for angular velocity: $$\dot {\vec r}=\vec \omega \times\vec r \tag{1}$$ does not hold in some situations, but the book does not specify what situation so please could you ...
30
votes
4answers
3k views

Can adding weight to something make it tilt slower?

Let's say we have 2 sticks, both a meter long. We put both of them on the ground vertically. To the top of one of them we attach a weight. Then we tip both of them over and let them fall. Assume ...
1
vote
1answer
107 views

Coupled wheel and rod (analytical mechanics) [closed]

I am struggling with formulating the equations of motion. Consider a coordinate system with origin in $O$ ($y$ upwards and $x$ to the right), label the center of mass of rod $AB$ with $G$ then: ...
1
vote
0answers
31 views

Rotational motion of a cylinder [closed]

I was solving a problem related to rotation, and cannot get to the exact answer. The question is as follows: A cylinder of mass $m$ rests on a carriage as shown. Calculate the maximum acceleration ...
2
votes
2answers
68 views

Does friction act on a wheel rolling at a constant speed

One of the things I've seemed to have taken for granted is that its the friction the floor exerts on a rolling wheel that prevents slip from occurring. However, I ran into something that challenges ...
0
votes
1answer
27 views

What happens with an originial force if a part of it creates a torque?

Let's say I push with an angle of 45 degrees at an object with a force of 100 N. Since the angle is 45, we would have a torque $\tau = 100 * sin(135) * r = 71N*r$ Since the force was not ...
2
votes
2answers
97 views

Conserved quantities in an angular system

Given the following question: A student initially stands on a circular platform that is free to rotate without friction about its center. The student jumps off tangentially, setting the platform ...
0
votes
1answer
32 views

Kinetic energy of disc pivoting about its edge

Suppose we have a disc of radius $R$ suspended vertically from a pivot on its edge. This disc is then given an initial angular displacement $θ$ and permitted to freely swing without friction. A ...
1
vote
0answers
20 views

What is happening kinematically to a car on an icy turn? [closed]

I am stumped on a conceptual homework question that involves rotational kinematics and friction. Consider a car traveling along a road that encounters a turn covered in an unseen layer of ice. ...
2
votes
1answer
126 views

When will the Earth stop rotating?

I looked up leap second in Wikipedia. It is a second added (usually) to clocks to keep them in sync with the atomic clock. It said that 25 leap seconds were added in the last 43 years and that none ...
1
vote
0answers
32 views

Torque due to non-uniform force [closed]

Suppose a non-uniform force, varying along with the distance, is acting normally on the surface of a rod hinged at the mid point. The force varies along the length of the rod, i.e as we go down along ...
4
votes
1answer
62 views

Optimal size for a bike tire

While I was riding my bike funnily enough I wondered if there was an optimal size for a bike wheel. So I suppose that is my question, What is the optimal size for a bike wheel? If the bike accelarates ...
1
vote
0answers
31 views

How to calculate angular momentum in this scenario? [closed]

The answer to part a) is 1080. However, for part b) I don't understand why the equation wouldn't simply be $I_i\omega_i = I_f\omega_f$. Why do we have to subtract $m_bv cos \phi$ from ...