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53 votes
5 answers
98k views

What did general relativity clarify about Mercury?

I frequently hear that Kepler, using his equations of orbital motion, could predict the orbits of all the planets to a high degree of accuracy -- except Mercury. I've heard that mercury's motion ...
Carson Myers's user avatar
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34 votes
5 answers
11k views

How do you calculate the anomalous precession of Mercury?

One of the three classic tests of general relativity is the calculation of the precession of the perihelion of Mercury's orbit. This precession rate had been precisely measured using data collected ...
David Z's user avatar
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33 votes
7 answers
19k views

Why don't spinning tops fall over?

One topic which was covered in university, but which I never understood, is how a spinning top "magically" resists the force of gravity. The conservation of energy explanations make sense, but I don't ...
Casebash's user avatar
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11 votes
2 answers
4k views

What happens to orbits at small radii in general relativity?

I know that (most) elliptic orbits precess due to the math of general relativity, like this: source: http://en.wikipedia.org/wiki/Two-body_problem_in_general_relativity I also know that something is ...
Alan Rominger's user avatar
7 votes
1 answer
1k views

Without using rotational mechanics, why does a gyroscope precess the direction it does?

When a top is spun, it will precess in some direction, either clockwise or counterclockwise. It's possible to find out which way using $\boldsymbol{\tau} = d\mathbf{L}/dt$ and $\boldsymbol{\tau} = \...
knzhou's user avatar
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5 votes
2 answers
2k 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 ...
Archisman Panigrahi's user avatar
4 votes
2 answers
14k views

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 expecting ...
Arlen Beiler's user avatar
2 votes
1 answer
423 views

Reasoning behind predicting a gyroscopes motion

Lets say we have a gyroscope that has a flywheel spinning with constant angular velocity. The gyroscope is held in place in a position where the massless metal rod connecting to the flywheel is ...
fibo11235's user avatar
  • 300
22 votes
5 answers
7k views

Why does a spinning top get back upright when knocked?

I have observed that, a spinning top, when toppled by knocking it with finger, becomes almost upright again (with negligible precessional motion), instead of undergoing precession while being heavily ...
Archisman Panigrahi's user avatar
13 votes
1 answer
1k views

Details of Newtonian Prediction for Mercury's Precession

Could anyone point me to a book or outline the methods used to actually calculate the 532 arcseconds per century that Newtonian theory apparently predicts for Mercury's precession. I am completely ...
13 votes
4 answers
6k views

What is the physics of a spinning coin?

When we spin a coin on a table, we observe 2 things: It slows down and stops after sometime. It does not stay at just one point on the table but its point of contact with table changes with time. I ...
Sahil Chadha's user avatar
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6 votes
2 answers
2k views

Mercury's Orbital Precession in Special Relativity

I am researching Mercury's orbital precession. I have considered most perturbations and general relativity. I am still not satisfied. I need your help. I need a solution to Exercise 13, Chapter 6, in ...
Raghu Singh's user avatar
4 votes
1 answer
2k views

Understanding the operation of Thomas precession

How can we physically understand the operation of Thomas Precession? Thomas Precession is an effect that modifies the effective energy of coupling between the spin and the orbital angular momentum ...
SRS's user avatar
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3 votes
5 answers
16k views

Direction of torque precession of a spinning wheel

Consider a spinning wheel, which is held up by one end of it's axis like this: To explain why the change of angular momentum is directed as shown in the figure above, one usually says that there is ...
martin's user avatar
  • 1,171
2 votes
1 answer
976 views

How was the neutron's spin measured?

In 2012 it was asked, How to measure the spin of a neutral particle. I'm not sure that the answer "Neutron spin can be measured in a Stern Gerlach setup." was really carried out. So what for ...
HolgerFiedler's user avatar
0 votes
4 answers
1k views

Why do bullets precess in the opposite direction from gyroscope diagrams?

Bullet spin causes a bullet to become a gyroscope. Specifically, bullets have their center of pressure in front of their center of mass. Therefore, when pressed, gyroscopic forces cause a bullet to ...
Johnlpmark's user avatar
10 votes
2 answers
525 views

Intuitive explanation of why orbits are closed?

Yesterday my brother asked me how orbits work. Suppose for the sake of the question that you are trying to put a rocket in orbit around the Earth. I explained that orbiting is essentially being in ...
Javier's user avatar
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6 votes
1 answer
432 views

Do 2-body elliptic orbits precess in special relativity?

Einstein famously explained the anomalous precession of Mercury by showing that in general relativity elliptic orbits precess even in the 2-body problem. But apparently in the early days of quantum ...
Conifold's user avatar
  • 5,353
5 votes
1 answer
468 views

Why can you assume that the angular momentum vector of a top will always track its axis of rotation?

My favorite physics 101 textbook (Giancoli) explains precession in terms of a spinning top whose axis is tilted from the vertical. The way the book sets things up, $L$ (angular momentum) points along ...
tel's user avatar
  • 255
5 votes
4 answers
1k views

Are elliptical orbits really elliptical?

I have wondered for a long time how elliptical orbits can work. It seems awkward for a freely-moving object to come very close to a source of gravity and then return to the exact point where it ...
Wutaz's user avatar
  • 394
4 votes
3 answers
2k views

Does the length of the sidereal day vary systematically?

I'm confused about some properties of the sidereal day, in particular whether its duration varies systematically over the course of the year.1 It seems to me that that must be the case, but the ...
orome's user avatar
  • 5,125
4 votes
1 answer
3k views

Minimum speed needed for a gyroscope to precess

I was reading about gyroscopes and their precession. Based on the text, the angular speed of precession is: $\omega_{precession}=\dfrac{\tau}{L}$ But intuitively, if the wheel of the gyroscope is ...
Soroush khoubyarian's user avatar
4 votes
1 answer
2k views

Newtonian contribution to perihelion precession of Mercury

We have seen that the orbits of the planets around the sun can be found, to a good approximation, by only considering a two-body system (a planet and the sun) interacting through a central force. ...
PG1995's user avatar
  • 717
3 votes
1 answer
1k views

Lagrangian of a precessing wheel: gyroscope in Lagrangian mechanics?

Let's consider this classical example: I would write the Lagrangian as the one of the spherical pendulum plus the rotational energy of the wheel, but I fail to see how the precession motion would ...
DarioP's user avatar
  • 5,175
3 votes
3 answers
601 views

Can precession happen with no external forces?

I wanted to ask the following question: Can a body that experiences no forces whatsoever precess? Let's say I have a body in space - no gravity or anything - can I make it precess without applying ...
GSofer's user avatar
  • 343
2 votes
2 answers
765 views

Gyroscope precession

I have a system diagrammed and explained in the image below. Experimentally I believe the wheel will rotate around the pivot point where the cable is attached in a counter-clock motion if observed ...
Addem's user avatar
  • 1,229
2 votes
3 answers
296 views

Is it possible to estimate the 23.5° tilt of Earth's axis?

Using the value of the precession of Earth's axis in 25,800 years and the value of Earth's radius, mass, moment of inertia etc., would it be possible to calculate/estimate that Earth's axis must be ...
Gerard's user avatar
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2 votes
1 answer
129 views

What explains the descrepancy between Asaph Hall's equation for Mercury's precession and GR?

In regard to What is the weight equation through general relativity?, the answer is: $$F=ma=\frac{GMm}{r^2}\frac{1}{\sqrt{1-\frac{2GM}{c^2r}}}.$$ This source provides a different equation: $$f \approx ...
HardlyCurious's user avatar
1 vote
1 answer
154 views

Derivation of precession rate of a wheel gyroscope [closed]

I searched on the web and all I could find is the precession rate of a spinning top. But what I want is the derivation of the precession rate of a wheel hanging from a rope, as shown below: which is ...
Sophile's user avatar
  • 410
1 vote
1 answer
153 views

Is Bertrand's Theorem Consistent with GR?

Bertrand's Theorem - Please observe the gif of orbits with different exponents in the denominator. (I couldn't get the image upload feature to work for this) Note, the orbit with a 1.9 exponent ...
HardlyCurious's user avatar
1 vote
0 answers
1k views

Direction change of gyroscopic precession with change in moment of inertia

In the classic bicycle wheel gyroscopic precession, using the right hand coordinate system of xyz and right hand rule of rotation, Such as X axis is in the longitudinal direction (spin axis) z axis ...
user50719's user avatar
1 vote
2 answers
303 views

About Mercury perihelion again

Sorry to bother you, but I did not get anywhere answer what exactly moves Mercury periapsis. "Sun gravity" or "GR" or "warp of spacetime" are very broad answers, I want to know how they affect this ...
ratschbumm's user avatar
1 vote
2 answers
486 views

How much force is required to break precession?

Gravity, in this diagram, provides a downward force creating a torque that causes the wheel to precess around the chain. This is cool but counter intuitive, and I am wondering what force is needed to ...
tranzfat's user avatar
0 votes
1 answer
983 views

Which force acts as centripetal force on gyroscope?

I think I have understood gyroscope in terms of angular momentum and how the torque of gravitational force moves it the way it does. Also I understand the direction in which it would move: What ...
Smit Chaudhary's user avatar
0 votes
1 answer
371 views

Purely mechanical description of how gravity causes a gyroscope to precess

I know the vector equation that relates torque to moment of inertia and angular momentum. What I want to know is what physical mechanisms actually occur to keep the gyroscope from falling. Where is ...
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