Satellite orbiting the Earth vs the moon?

In summary, the moon does not fall into the Earth due to it's pseudo centrifugal force due to the opposing of linear inertia and also due to the fact that it does not lose velocity. The centrifugal force, which exists only in rotating reference frames, opposes the gravitational attraction.
  • #1
shangriphysics
32
1
I know that the the satellite will lose speed(due to perhaps small air resistance), and therefore lose centripetal force? I am not sure how losing centripetal force and speed causes the satellite in orbit to lose radius. If force is the same, and velocity is lowered, than radius would increase.

I think that the moon does not fall into the Earth due to it's pseudo centrifugal force due to the opposing of linear inertia and also due to the fact that it does not lose velocity.
 
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  • #2
I know that the the satellite will lose speed(due to perhaps small air resistance), and therefore lose centripetal force? I am not sure how losing centripetal force and speed causes the satellite in orbit to lose radius. If force is the same, and velocity is lowered, than radius would increase.
As a satellite gets closer - it gains centripetal force from gravity. The drag is an additional force applied tangentially to the orbit.

Consider - if removing speed leads to a higher orbit, then that would mean that taking energy away will lift it.
Usually you expect to give something energy to lift it higher don't you?

I think that the moon does not fall into the Earth due to it's pseudo centrifugal force due to the opposing of linear inertia and also due to the fact that it does not lose velocity.
... please clarify that sentence - it seems pretty mangled.
You are saying the Moon stays up because ... it does not slow down and it's linear inertia is balanced by centrifugal force? Something like that? It doesn't make a lot of sense. Forces balance forces, not inertia.
Eg. for a satellite in a circular orbit, the centrifugal force is needed to balance the gravitational force (in a reference frame where the satellite and primary are stationary).
Also - the Moon does slow down in it's orbit - and gets farther away.
http://en.wikipedia.org/wiki/Tidal_acceleration

But you should not be advancing personal theories in PF - try asking a question about why the Moon stays up instead.
 
  • #3
shangriphysics said:
If force is the same, and velocity is lowered, than radius would increase.
Nope. Same sideways acceleration at less velocity produces a more curved path, with a lower radius of curvature.

shangriphysics said:
I think that the moon does not fall into the Earth due to it's pseudo centrifugal force due to the opposing of linear inertia
Nope. The centrifugal force, which exists only in rotating reference frames, opposes the gravitational attraction. But a general (frame-independent) explanation shouldn't even involve frame-dependent forces, like the centrifugal force.
 
  • #4
shangriphysics said:
If force is the same, and velocity is lowered, than radius would increase.
I remember a freshman undergrad physics course that used a sloppily written book which propagated this misconception. Reading it confused me out of the wazoo back then.
The idea is that since a circular orbit has got a lower orbital speed the larger the radius, then a conclusion is reached that to increase the radius of the orbit one needs to decelerate.
The above is of course completely incorrect.

Here's a free browser-based game called Voar:
http://voar.io/
It let's you fly a spaceship around a planet. The only control you've got over your craft is the forward thruster. Playing a bit can help gain an intuition of how orbits work.

There are also other, more involving games out there that can help you learn orbital mechanics first hand. This one here:
http://orbit.medphys.ucl.ac.uk/
is a full blown spacecraft simulator.

For gaining mathematical intuition, probably the best way is, as mentioned by Simon, to use the conservation of energy. Write down the potential+kinetic energy of the ship/satellite at a given radius, add some KE (that is, increase velocity), and try to figure out how the two change, keeping in mind that the total has to remain the same (unless you fire the rockets again).
 
  • #5
Ahh thanks you guys!

Quick question, are the forces on the moon perfectly in balance with the force of gravity, so that it would not come crashing down, and if so, could we possibly have a satellite mimick this phenomena and therefore have it stay up in orbit until the Earth gets destroyed?
 

1. How does the orbit of a satellite around the Earth differ from its orbit around the Moon?

The main difference between the orbit of a satellite around the Earth and its orbit around the Moon is the distance from the center of gravity. The Earth is much larger and has a stronger gravitational pull on objects, causing satellites to have a faster orbital speed and a shorter orbital period compared to the Moon. Additionally, the Earth's orbit around the Sun is much larger than the Moon's orbit around the Earth, resulting in a wider orbital path for Earth-orbiting satellites.

2. Why do satellites orbit at different altitudes around the Earth and Moon?

The altitude of a satellite's orbit around the Earth or Moon is determined by the specific mission requirements. Some satellites, such as those used for communication or navigation, may need to be in a higher orbit to provide wider coverage, while others, such as weather satellites, may need to be in a lower orbit to gather more detailed data. The Moon's orbit is also affected by the Earth's gravity, which can cause variations in its distance from the Moon.

3. Can satellites orbit both the Earth and the Moon simultaneously?

Yes, it is possible for a satellite to orbit both the Earth and the Moon simultaneously. This type of orbit is known as a halo orbit, where the satellite follows a curved path around the Lagrange point, a point where the gravitational forces of the Earth and Moon cancel each other out. This allows the satellite to maintain a relatively stable position between the two bodies.

4. How does the orbit of a satellite affect its communication capabilities?

The orbit of a satellite can greatly affect its communication capabilities. Satellites in low Earth orbit (LEO) have a shorter distance to travel for signals, resulting in a lower signal delay and faster data transmission. However, LEO satellites have a shorter coverage area and require more satellites for global coverage. Satellites in geostationary orbit (GEO) have a higher coverage area but also experience a longer signal delay due to their farther distance from Earth.

5. Can a satellite's orbit around the Moon be affected by other celestial bodies?

Yes, a satellite's orbit around the Moon can be affected by other celestial bodies, such as the Sun and other planets. This is known as perturbation, where the gravitational pull of these bodies can cause slight changes in the satellite's orbit. This is taken into account when designing and operating satellites around the Moon to ensure their intended orbits are maintained.

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