Gravity Invariant with Motion? Exploring Examples

In summary: Don't moving charges also have constant acceleration in the direction of the field?The acceleration of a charged particle in an electric field is constant, but in a magnetic field the acceleration is perpendicular to the velocity. Without considering the change in distance, is the force (local instantaneous) between moving charges also constant regardless of the relative motion of the charges?Yes, the force between moving charges is constant regardless of their relative motion. This is due to the Lorentz force law, which takes into account both the electric and magnetic fields. In summary, the conversation discusses the concept of constant acceleration in various scenarios, such as with a ball in flight and moving charges. It also touches on the idea of inertial reference frames and the effects of
  • #1
bahamagreen
1,014
52
In simple examples of throwing a ball upward and observing it's arc, the calculations include a constant vector acting downward on the ball throughout it's flight. Without getting into the complications of that vector changing magnitude with altitude, it does not change with respect to the speed of the ball... it is a constant acceleration in the direction of the field.

So when the ball is at peak altitude v = 0 that vector is g = -x
And, when the ball is moving in flight that vector is still g = -x

Now that does not seem so strange because as a geodesic perspective the local curvature is what it is despite the apparent change in the ball's speed. Is the ball's 4speed locally constant?

But since the ball is in free fall can I take it as an inertial reference frame and imagine the Earth receding, pausing, and approaching, because where would the energy come from for it to accelerate like that? But in either case, it then looks like the gravitational force is a constant regardless of the relative motion of the source (Earth) or observer (ball).

Don't moving charges also have constant acceleration in the direction of the field? Without considering the change in distance, is the force (local instantaneous) between moving charges also constant regardless of the relative motion of the charges?

I'll pause here to learn if I'm already off the rails before advancing more questions...
Thanks :)
 
Physics news on Phys.org
  • #2
bahamagreen said:
...I take it as an inertial reference frame and imagine the Earth receding...
It's only locally an inertial frame, not when you extend it to include the entire Earth.
 
  • #3
bahamagreen said:
Is the ball's 4speed locally constant?
Yes. The norm of the four velocity is always c. It is essentially normalized to make that true.

bahamagreen said:
imagine the Earth receding, pausing, and approaching, because where would the energy come from for it to accelerate like that?
There is an unbalanced real force pushing upwards which caused the acceleration. If you follow the energy flow you pretty quickly get to a point where you cannot use the flat spacetime local approximation any more.

bahamagreen said:
But in either case, it then looks like the gravitational force is a constant regardless of the relative motion of the source (Earth) or observer (ball).
The gravitational force is 0 in the local inertial frame, by definition. It is nonzero in the ground frame, which is non inertial.
 

1. What is gravity invariant with motion?

Gravity invariant with motion is a concept in physics that states that the force of gravity is not affected by the motion of an object. This means that regardless of the speed or direction of an object, the force of gravity acting on it remains constant.

2. How is this concept different from Newton's law of universal gravitation?

Newton's law of universal gravitation states that the force of gravity between two objects is directly proportional to their masses and inversely proportional to the square of the distance between them. Gravity invariant with motion, on the other hand, focuses on the effect of an object's motion on the force of gravity.

3. Can you provide an example of gravity invariant with motion?

One example of gravity invariant with motion is the orbit of a satellite around the Earth. The force of gravity between the satellite and the Earth remains constant, regardless of the satellite's speed or direction of motion.

4. How does Einstein's theory of relativity relate to gravity invariant with motion?

Einstein's theory of relativity states that the laws of physics are the same for all observers regardless of their relative motion. This includes the force of gravity, which is not affected by an object's motion. Therefore, gravity invariant with motion is consistent with Einstein's theory of relativity.

5. Why is understanding gravity invariant with motion important?

Understanding gravity invariant with motion is important because it helps us accurately predict the motion of objects in the presence of gravitational forces. It also allows us to make precise calculations and observations in fields such as astrophysics and space travel.

Similar threads

  • Special and General Relativity
Replies
7
Views
930
  • Special and General Relativity
Replies
23
Views
2K
  • Special and General Relativity
2
Replies
36
Views
3K
  • Special and General Relativity
Replies
15
Views
1K
  • Special and General Relativity
Replies
11
Views
1K
  • Special and General Relativity
Replies
13
Views
2K
  • Introductory Physics Homework Help
2
Replies
38
Views
1K
Replies
32
Views
852
  • Special and General Relativity
Replies
4
Views
1K
  • Special and General Relativity
2
Replies
39
Views
2K
Back
Top