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Old 03-08-2017, 01:15 AM
 
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In outer space do objects travel at constant speed or do they always either accelerating or decelerating?

Like if I fire gun in space, will bullet travel at the speed of muzzle velocity forever, or will it keep accelerating at whatever it was accelerating? And with nothing else effecting it.

Are all objects that move always just accelerating or decelerating, and no such thing as constant, or uniform speed except for radiation?

Does the sun, earth, moon, all pivot and rotate at constant speed or is it acceleration/deceleration. What about Haley's comet?
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Old 03-08-2017, 06:34 PM
 
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Quote:
Originally Posted by NJ Brazen_3133 View Post
In outer space do objects travel at constant speed or do they always either accelerating or decelerating?

Like if I fire gun in space, will bullet travel at the speed of muzzle velocity forever, or will it keep accelerating at whatever it was accelerating? And with nothing else effecting it.

Are all objects that move always just accelerating or decelerating, and no such thing as constant, or uniform speed except for radiation?

Does the sun, earth, moon, all pivot and rotate at constant speed or is it acceleration/deceleration. What about Haley's comet?
The rate of earth's rotation is gradually slowing, but the rate at which it is slowing is so slight that an atomic clock is required to measure the change. According to NASA, in 100 years a day on earth will be about 2 milliseconds longer than today. This is due to tidal forces resulting from the moon as it orbits the earth.
We can use extremely accurate atomic clocks to measure exactly how much the rotation is slowing down. One hundred years from now, a day will be about 2 milliseconds longer than today. Two milliseconds is 1/500th of a second, or how long it takes a car going 55 mph to travel only 2 inches--in other words, much less than the blink of an eye. So, if you live to be 100, you can't complain that the days are getting shorter! At this rate, though, you don't have to worry about the days getting enough longer to change things very much.

https://spaceplace.nasa.gov/review/d...-rotation.html
A note of interest is that the 2004 Sumatran earthquake actually increased the earth's rotational speed by about three microseconds. - Sumatran quake sped up Earth's rotation : Nature News

Although the same side of the moon always faces the earth, it actually rotates. The moon's rate of rotation varies due to an elliptical orbit. As the moon's distance from the earth changes, its rate of rotation changes. As the moon's distance from earth increases it's rotational rate also increases. As the moon gets closer to earth its rotation slows. You can read up on that in this article at space.com - Does the Moon Rotate?

I haven't checked the figures on Haley's comet but since it has a highly elliptical orbit around the sun its speed varies as its distance from the sun changes.
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Old 03-08-2017, 07:28 PM
 
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Originally Posted by Mike555 View Post
The rate of earth's rotation is gradually slowing, but the rate at which it is slowing is so slight that an atomic clock is required to measure the change. According to NASA, in 100 years a day on earth will be about 2 milliseconds longer than today. This is due to tidal forces resulting from the moon as it orbits the earth.
We can use extremely accurate atomic clocks to measure exactly how much the rotation is slowing down. One hundred years from now, a day will be about 2 milliseconds longer than today. Two milliseconds is 1/500th of a second, or how long it takes a car going 55 mph to travel only 2 inches--in other words, much less than the blink of an eye. So, if you live to be 100, you can't complain that the days are getting shorter! At this rate, though, you don't have to worry about the days getting enough longer to change things very much.

https://spaceplace.nasa.gov/review/d...-rotation.html
A note of interest is that the 2004 Sumatran earthquake actually increased the earth's rotational speed by about three microseconds. - Sumatran quake sped up Earth's rotation : Nature News

Although the same side of the moon always faces the earth, it actually rotates. The moon's rate of rotation varies due to an elliptical orbit. As the moon's distance from the earth changes, its rate of rotation changes. As the moon's distance from earth increases it's rotational rate also increases. As the moon gets closer to earth its rotation slows. You can read up on that in this article at space.com - Does the Moon Rotate?

I haven't checked the figures on Haley's comet but since it has a highly elliptical orbit around the sun its speed varies as its distance from the sun changes.
I was going to mention the elliptical orbit thing. In an elliptical, you can speed up and slow down, speed up and slow down. Is that the only instance when that can occur?

Also is everything rotating around something? Or are there any objects in universe that travel in straight or curve but is not tethered to anything?
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Old 03-08-2017, 09:02 PM
 
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Originally Posted by NJ Brazen_3133 View Post
I was going to mention the elliptical orbit thing. In an elliptical, you can speed up and slow down, speed up and slow down. Is that the only instance when that can occur?

Also is everything rotating around something? Or are there any objects in universe that travel in straight or curve but is not tethered to anything?
The principle of inertia is such that an object at rest will remain at rest, an object in motion will remain in motion, and the direction of a moving object will remain constant unless and until it is acted upon by an external force. You really can't get away from gravity as it exists everywhere in the Universe. Neighboring galaxies are gravitationally attracted to each other. As far away as the voyager 1 craft is from the sun (and I don't know what its distance from the sun is currently) it is still being gravitationally acted upon by the sun and its speed is constantly being slowed down over time.

Objects that rotate, rotate around their own axis. Earth rotates around its axis, our galaxy rotates around its center. But perhaps you meant to ask about whether everything revolves or orbits something else. Moons revolve around their planets, a planet and its moon revolve or orbit around a common center called a barycenter, planets revolve around their stars. A star and its planet has a barycenter.

The illustration below shows the barycenter around which both Pluto and its moon orbit.


pluto moon barycenter - Bing images

The barycenter of the earth and moon actually is within the earth itself as seen in this diagram.


earth moon barycenter - Bing images

A star and its planet or planets has a barycenter. As a planet orbits its star it causes the star to wobble as it moves around or at least in relation to its barycenter.

The sun Jupiter barycenter is shown below.


earth sun barycenter - Bing images
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Old 03-08-2017, 11:57 PM
 
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But then what about accelerating, decelerating or constant speed? Is everything always accelerating when moving or decelerating or can something remain at constant speed if nothing affects it?

Like the bullet example. If bullet muzzle velocity is like 2300 meters/second, does it keep going at that rate, or does it get faster?
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Old 03-09-2017, 12:36 AM
 
Location: Somewhere in northern Alabama
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The bullet remains at the velocity... sorta. What you are asking was fisrt year high school physics when I was growing up. F=MV , conservation of energy, etc.

When I say the bullet velocity remains the same... sorta... I recognize that gravity permeates the universe, and there will be infinitesimal changes in speed because of the gravity of the Earth, Sun Jupiter, Saturn, black hole at the galactic center, neutron stars, and hot dogs on Coney Island.
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Old 03-10-2017, 12:31 AM
 
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Originally Posted by harry chickpea View Post
The bullet remains at the velocity... sorta. What you are asking was fisrt year high school physics when I was growing up. F=MV , conservation of energy, etc.

When I say the bullet velocity remains the same... sorta... I recognize that gravity permeates the universe, and there will be infinitesimal changes in speed because of the gravity of the Earth, Sun Jupiter, Saturn, black hole at the galactic center, neutron stars, and hot dogs on Coney Island.
Well when the bullet starts out in the chamber, it must accelerate up to the muzzle velocity. Will it keep accelerating at that pace, meaning gets faster and faster, or will continue uniformly stay at the muzzle velocity, and never get faster?
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Old 03-10-2017, 01:22 AM
 
Location: Somewhere in northern Alabama
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Muzzle velocity. The area you are interested in is ballistics. There should be ample resources to give detail.
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Old 03-10-2017, 02:23 AM
 
Location: Brackenwood
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The bullet will stop accelerating once the force that causes it to accelerate stops acting upon it, which is to say, it would reach and maintain its muzzle velocity. If that bullet were the only object or matter or energy source in space besides the gun that fired it, then yes it would continue on its course and velocity in perpetuity, as would the gun in the opposite direction. In reality, there will be other forces acting on it such as particles, gases, gravity sources like stars and planets and nebulae, etc But the way you frame your question with regard to earth's orbit and what not is inapplicable. Any change in direction is an acceleration, so any body in orbit around another is in a perpetual state of acceleration even if the speed of orbit never changes.

Last edited by Bitey; 03-10-2017 at 02:34 AM..
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Old 03-11-2017, 12:08 AM
 
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Even in a vacuum such as outer space without any kind of friction? Is it because of gravity? But if gravity is acting on it, is it no decelerating?
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