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40 views

Objects Rolling Downhill - Ratio of Rotational and Translational Kinetic Energies [on hold]

Let's say I roll a uniform disk down a ramp (without slipping), and the disk rolls 10 meters down the ramp which is angled at 30 degrees to the horizontal. At the bottom of the ramp, what is the ratio ...
0
votes
1answer
39 views

Kinetic Energy Comparison Marble Question

A uniform marble of mass M rolls down a symmetric bowl, starting from rest at the top of the left side. The top of each side is a distance h above the bottom of the bowl. The bowl is rough enough to ...
1
vote
3answers
252 views

Rotational KE vs Translational KE [closed]

Q. Horizontal electric field E = mg/q exists as shown in the figure and a mass m is attached at the end of a light rod. if mass m is released from the position as shown in the figure. find the angular ...
0
votes
1answer
32 views

Rolling on a track in vertical plane

A sphere of mass m and radius r is released from rest at point A on a track in vertical plane. The track is rough enough to support rolling between A and B and from B onwards it is smooth. My ...
12
votes
8answers
6k views

Does it take energy to move something in a circle?

Work can be calculated by $W = Fd\cos\theta$ where $\theta$ is the angle between the force $F$ and the displacement $d$ Let's say there's a ball and a (physically ideal - no friction etc.) robotic ...
0
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4answers
196 views

Can you derive the acceleration of a cylinder rolling down an inclined plane by ONLY using conservation laws?

I want to solve the standard problem of a cylinder rolling down an inclined plane by only using conservation laws. In particular I want to use the equation: $$E_{pot}=\frac{1}{2}mv^2+\frac{1}{2}I\...
1
vote
1answer
117 views

Conservation of energy in rotational motion [duplicate]

Suppose a boy is standing on a platform which is free to rotate about an axis passing through its center. The Kinetic energy of the boy and the platform is K. If the boy stretches his hands so that ...
-1
votes
1answer
89 views

Violation of energy conservation during collisions of a particle with different sections of a rod [closed]

Imagine a homogenous rod with total mass $M$ and length $l$ floating in free space without any force or constraint acting on it. Then, think about two possible scenarios. In the first, a particle with ...
-1
votes
3answers
44 views

Rolling friction and motion [duplicate]

The frictional force in a motion of a rolling body is along the direction of motion. Then what stops the motion of a rolling body?
2
votes
4answers
105 views

Why does force x distance not equal kinetic energy for objects rolling down an inclined plane?

Imagine two objects at rest at the top of an inclined plane which are capable of rolling and which are identical in every way (mass, radius, etc) with the exception of how their mass is distributed. ...
1
vote
3answers
81 views

How does a cilinder that rolls without slipping lose energy? [duplicate]

Suppose a cilinder that rolls without slipping on a horizontal rough surface. The slipping is prevented by friction, which therefore slows it down, so it loses kinetic energy. But no dissipative work ...
2
votes
3answers
242 views

Why pure rolling's energy is conserved?

Although there exists non-conservative force during pure rolling (for this, static friction), why is energy conserved? Is it just special feature of pure rolling?
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2answers
72 views

Ballerina Energy clarification

There is similar question on this but I have a specific issue that needs clarification. For the classic example of the ballerina spinning, on extension angular speed decreases, and on retraction ...
-1
votes
1answer
133 views

Speed of a hollow cylinder at end of incline plane. Confusion about Conservation of Energy [closed]

A hollow cylinder is rolling down an inclined plane. We have to get the speed of the center of mass of the cylinder at the end of the inclined plane. Energy Conservation tells us: $$ mg(h + R) = \...
-1
votes
1answer
95 views

Motion of a rotating object in space

What will happen if connect an iron rod with a motor's axis and rotate it in space and after a while disconnect the motor's axis from the rod. Will after this the rod show infinity motion and if not ...
0
votes
1answer
186 views

Is angular work equivalent to linear work?

When considering the definition of angular work, I assumed that it should reduce to the definition of linear work in order to tie in quite nicely with conservation of energy. However, further ...
0
votes
1answer
213 views

Inclusion/Exclusion of linear kinetic energy in a rope-pulley system

I find it difficult why in the first problem the linear kinetic energy is not included in the calculation, but in the second it is included, yet the questions are virtually the same.
1
vote
2answers
98 views

Which ball spins the longest?

I just thought of a mind-boggling question about angular velocity and friction. Here is the picture: The first figure shows a ball spinning around the y-axis, and the seconds shows another ball that ...
2
votes
3answers
3k views

Rotational kinetic energy when moment of inertia is changed

The following quote comes from: https://physics.stackexchange.com/a/93531/155365 Consider an ice skater that has just gone into a spin with arms stretched out. If it helps, the skater is wearing ...
0
votes
1answer
893 views

If the angular momentum is conserved in a system whose moment of inertia is increased, it's kinetic energy decreases [duplicate]

The workout that $\Delta K.E.$ is less than zero is attached. But where does this energy go. It is transformed back to rotational KE if moment of inertia decreases. How would you account for the ...
0
votes
1answer
28 views

What is the energy of a body that rotates in an unfixed radius?

I have a body $m$ that is in a track that limits it's movment only to the radial axis. He is connected to a spring and that track is rotating around the same axis as shown here : I wonder what is ...
1
vote
1answer
1k views

Curved Slope faster than linear?

So I saw this gif the other day, and was wondering, is this real or fake? And supposing there is no energy dissipated by the friction, why does such thing occur?
4
votes
1answer
866 views

What gives energy for precessional motion of gyroscope?

Let us suppose we have an ideal friction-less gyroscope and it is suddenly given an angular momentum, and left as in the figure. It will start precessional motion. Since there is no friction, the ...
0
votes
2answers
53 views

Rotational velocity of tethered shape after falling

My solution to the above question involves equating the potential energy to the to the kinetic energy at the point at which the wire tightens as: $$ \frac{1}{2}mv^2 = mgh $$ However, I am having ...
4
votes
2answers
464 views

Using conservation of kinetic energy to find angular momentum after a collision

I'm self-studying so sadly I don't have a professor or classmate to ask this to. I'm mostly learning through Khan Academy which is where I came across this question: A ball of mass $M$ is rolling ...
0
votes
1answer
236 views

Unexplained energy loss of 50% when calculating potential vs. kinetic energy

I did a lab where we did this experiment with four different solids. It's a conservation of energy lab, so we calculated the potential energy at the beginning of the incline ($mgh$) and the kinetic ...
5
votes
1answer
3k views

Why does a rolling sphere stop?

I've just started studying Rotational Mechanics and one thing I'm confused about is that if friction is equal to zero when a body is rolling purely.. then why does a rolling body e.g. sphere.. stop ...
2
votes
1answer
76 views

The height traveled by the mass center of a thrown rod

I'm learning Newtonian mechanics and want to understand the following example and the methods I can use for it. Suppose I throw a rod in the air with length $L$. The time I'm letting go of the ...
-2
votes
2answers
100 views

Is there any danger of gravity being used up? [duplicate]

Posit a way to harness gravity for energy and widespread use of this new technology world-wide. Could it be damaging to Earth, over a few hundred years, slowing or speeding up rotation or the orbit ...
0
votes
1answer
66 views

Galaxy equillibrium

I know this is a very dumb question, but, to maintain a galaxy as a bounded system, the total energy and the total angular momentum of every particle component of the galaxy (suppose made of gas and ...
-1
votes
2answers
530 views

Rotation of rigid body after inelastic collision with smaller mass

A slender rod of length $l$, with no mass, is able to rotate around an axis through its center, with no friction. There are two points of mass $M$ and negligible radius attached to each end of the rod....
6
votes
1answer
5k views

What is rotational potential energy?

I don't understand the concept of rotational potential energy. During linear motion, when a force is applied, the work it does gets converted to kinetic energy and there is no change in the ...
0
votes
1answer
69 views

Spheres collide with merry-go-round [closed]

Four spheres, with uniform densities $\rho_1, \rho_2, \rho_3, \rho_4$ and radii $r_1, r_2, r_3, r_4$, respectively, roll without slipping with constant velocities $v_1, v_2, v_3, v_4$ along tracks ...
0
votes
1answer
364 views

Energy method to solving equations of motion? Why does this method work and what is it called?

Given the stated system in the photo we are suppose to prove simple harmonic motion when given an initial displacement $x$ I first considered the total energy of the system which we will call $H$ $$H=...
0
votes
1answer
129 views

A sphere rolling down a plank - an error in calculating its energy

Consider the following situation: A sphere with radius $r$ rolls down a plank which forms an angle $\theta$ with the horizontal axis. The starting hight of the centre of mass is $h$. We assume that ...
-1
votes
1answer
75 views

Why does this consider the center of mass instead of the end? (RIGID BODY MOTION) [closed]

A uniform rod of length L and mass M is free to rotate on a frictionless pin passing through one end. The rod is released from rest in the horizontal position. What is its angular speed when it ...
1
vote
0answers
132 views

Uranus, the Physical model to change its rotation axle

Uranus rotates pretty wierd, it's 90-degrees tilted; Why is Uranus's axis of rotation tilted? The best answer for this is; that at a distant point in its past, Uranus was struck by a very ...
7
votes
4answers
1k views

Earth's Kinetic energy change

Earth's rotational speed varies. I have checked the data an found following Peaks; Year 1998, 23.May, the Earth rotated in 86400.0023738 seconds. At 9.July the rotation time of the Earth was 86400....
1
vote
2answers
1k views

Conservation of Energy vs Conservation of Momentum in Rotational Dynamics

It is clear to me why angular momentum is always conserved, and how in some cases energy is not necessarily conserved within the system (in those cases where bodies deform, or friction is involved). ...
2
votes
1answer
99 views

Spinning rubber ball with equatorial ridge

I have this rubber ball with something like a very slight equatorial ridge (sort of like Saturn's moon Iapetus) which I often spin around on my desk. I keep noticing that no matter the inclination of ...
2
votes
1answer
1k views

Ball rolling on half-pipe

It is well-known that a ball rolling down a half-pipe where the side it starts on has enough friction for the ball to roll without slipping and on the side other to be frictionless, that the ball will ...
0
votes
3answers
3k views

Finding the angular velocity of a rod hit at a distance from its pivot [closed]

A 1m long, 2kg stick is nailed to the wall with a single nail, allowing it to pivot and freely rotate at the end. A 1kg ball, with speed 3m/s makes contact with the stick at some distance x (unknown) ...
1
vote
1answer
133 views

Determine the value of $g$ with rolling ball

At first, I thought the value of $g$ ($9.8m/s^2$) could be determined simply by placing a ball at the top of a ramp at a known height. The ball was released with no initial velocity, and the final ...
0
votes
1answer
421 views

An unwinding cable problem [closed]

Suppose a light cable is wrapped around a solid cylinder with mass $M$ and radius $R$. The cylinder rotates with no friction about a stationary horizontal axis. The free end of the cable is attached ...
2
votes
0answers
366 views

Friction and work from torque

I would like to understand where is the error in the third case, for that I gave 2 easier cases where I'm able to find the energy from heating is equal to the energy lost by torque. Case 1/ Purple ...
1
vote
1answer
327 views

What prevents this rotational perpetuum mobile from working? [closed]

As a newbie in physics I imagine this device and I would like to know why it can't increase its energy. Note I study the sum of energy during one second (or less) after set friction ON. The device: ...
5
votes
2answers
303 views

I need help figuring out what is wrong in this aspiring perpetuum mobile

Credits: My question is motivated from a question from another user (https://physics.stackexchange.com/q/143377/), I just reformulated what I think he tried to ask into, what seem to me, simpler terms....
2
votes
0answers
241 views

Sum of energy from torques of several disks in double rotation [closed]

Here the study: An external system (not drawn) give energy for rotate disks around themselves and around green axis. All disks have energy at start, at $t=0$ friction is ON and at $t=0$ external ...
1
vote
1answer
348 views

Gravitational Potential Energy to Kinetic Energy

When a yo-yo is released from a height $h$, the gravitational potential energy is converted to kinetic energy. However, the yo-yo obviously has less acceleration than $g$, $9.8\frac{m}{s}$. This means ...
5
votes
2answers
1k views

How to model energy loss in a rotating body?

I recently asked a question about modeling instability in a rotating rigid body. I now realize that I was mentally confounding two different effects: The "Dzhanibekov effect" in which a rigid object ...