Terminal velocity in a vacuum.

In summary, there is a terminal velocity for an object in free fall in a gravitational field based on the strength of that field. If I was falling to Earth and there was no atmosphere, and I had infinite time to fall(Meaning I'd never actually reach the surface) would the strength of Earth's gravity determine the maximum velocity I could achieve?
  • #1
tkav1980
47
1
I am curious if there is a terminal velocity for an object in free fall in a gravitational field based on the strength of that field. If I was falling to Earth and there was no atmosphere, and I had infinite time to fall(Meaning I'd never actually reach the surface) would the strength of Earth's gravity determine the maximum velocity I could achieve?
 
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  • #2
Not exactly sure what you mean. If you mean: Imagine the Earth with no atmosphere and you dropped an object from infinity (ignoring other masses, of course)? Then the mass and radius of the Earth would determine the speed with which the object hits the surface.
 
  • #3
Doc Al said:
Not exactly sure what you mean. If you mean: Imagine the Earth with no atmosphere and you dropped an object from infinity (ignoring other masses, of course)? Then the mass and radius of the Earth would determine the speed with which the object hits the surface.

Imagine being infinitely far away form the Earth yet still able to experience its gravity with the same force as it is felt on earth. You are also in a vacuum falling towards earth. Since you are infinitely far away you will never reach it. Is there a point where the strength of Earth's gravity can no longer increase your velocity? Is there an upper speed limit relative to the strength of the gravitational pull from a given body?
 
  • #4
tkav1980 said:
Is there a point where the strength of Earth's gravity can no longer increase your velocity? Is there an upper speed limit relative to the strength of the gravitational pull from a given body?
Yes. Your speed with respect to the Earth will never exceed the speed of light.
 
  • #5
Doc Al said:
Yes. Your speed with respect to the Earth will never exceed the speed of light.

Thank you, that was my first intuition, but that leads me to the source of my question. If an objects mass increases relative to its velocity, where aproaching c that mass approaches infinity, the energy required for more acceleration also approaches infinity. What I am not quite understanding is if gravity is a curvature of space what is the source of energy for acceleration due to gravity? I, and this is oversimplification on a grand scale I know, picture gravity like the old ball on a rubber sheet. Where the ball is simply rolling down a hill. So what is the source of the energy needed for acceleration and why is this limited to below c?
 
  • #6
Let's leave general relativity aside. You've created an artificial situation, a constant gravitational field that extends to infinity. (An infinitely high hill.) So that gravitational potential energy is the source of the energy.

From special relativity, we know that as the the speed of an object approaches the speed of light, it takes more and more energy to attain an increase in speed. It would require 'infinite' energy to reach the speed of light itself.
 
  • #7
Doc Al said:
Let's leave general relativity aside. You've created an artificial situation, a constant gravitational field that extends to infinity. (An infinitely high hill.) So that gravitational potential energy is the source of the energy.

From special relativity, we know that as the the speed of an object approaches the speed of light, it takes more and more energy to attain an increase in speed. It would require 'infinite' energy to reach the speed of light itself.

Ahh, I see your point. Thank you for taking the time to answer my questions.
 
  • #8
Where is it written that gravity, the force that accellerates all matter equally, regardless of mass, is in any way dependant on the speed and/or increased mass of the object. It should take approximately 9360 hours to reach the speed of light at a rate of 9m/sec/sec.
 
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  • #9
dtyarbrough said:
Where is it written that gravity, the force that accellerates all matter equally, regardless of mass, is in any way dependant on the speed and/or increased mass of the object.
It's not that gravity (or the resulting proper acceleration) depends on the speed, but the effect of that acceleration does.
It should take approximately 9360 hours to reach the speed of light at a rate of 9m/sec/sec.
Only if you ignore the lessons of special relativity. Speeds don't add like they do in Newtonian physics. Even though the proper acceleration remains 9.8 m/s2 (say), with each succeeding second, the speed increase with respect to an outside frame (the earth) is less. It never reaches the speed of light.
 
  • #10
tkav1980 said:
Imagine being infinitely far away form the Earth yet still able to experience its gravity with the same force as it is felt on earth. You are also in a vacuum falling towards earth. Since you are infinitely far away you will never reach it. Is there a point where the strength of Earth's gravity can no longer increase your velocity? Is there an upper speed limit relative to the strength of the gravitational pull from a given body?

As was mentioned, this scenario is a VERY artificial scenario, as even Newton knew that the force of graviy falls off exponentially as you go further away from a planet. So even if you're on the edge of the universe, Earth's gravity will still attract you, although by an infinitesmally small amount.

Anyway, what this all means is that indeed there is a limit to how fast Earth's gravity will accelerate you. If you started out very far away at rest, Earth's gravity could only get you going at ~11 km/s. This is known as escape velocity. Each body has one. It's also how fast you must go to escape Earth's gravitational field. The moon missions and every space mission far away from Earth had to achieve at least this speed. It's also the minimum speed at which an asteroid will hit Earth's atmosphere.

Earth's gravity will ALWAYS keep slowing you down, but as you fly further away it slows you down less and less. If you're at escape velocity then you will always essentially be "outrunning" Earth's gravity, so that it always slows you down but can never slow you down completely.

The escape velocity at a black hole's event horizon is the speed of light.
 
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  • #11
tkav1980 said:
I am curious if there is a terminal velocity for an object in free fall in a gravitational field based on the strength of that field. If I was falling to Earth and there was no atmosphere, and I had infinite time to fall(Meaning I'd never actually reach the surface) would the strength of Earth's gravity determine the maximum velocity I could achieve?
It's worth mentioning that the origin of terminal velocity is an essentially constant force in one direction (gravity) opposed by a force in the opposite direction which increases with speed (air resistance). The two balance at exactly one speed. That speed is the "terminal velocity".

In empty space there is no resistance opposing gravity. Hence no terminal velocity.
 

What is terminal velocity in a vacuum?

Terminal velocity in a vacuum is the maximum velocity that a falling object can reach when the only force acting upon it is gravity. In a vacuum, there is no air resistance to slow down the object, so it will continue to accelerate until it reaches its terminal velocity.

How is terminal velocity in a vacuum calculated?

The formula for calculating terminal velocity in a vacuum is v = √(2mg/ρAC), where v is the terminal velocity, m is the mass of the object, g is the acceleration due to gravity, ρ is the density of the object, A is the cross-sectional area of the object, and C is the drag coefficient of the object.

Why is terminal velocity in a vacuum important?

Understanding terminal velocity in a vacuum is important in fields such as physics and engineering. It helps us predict how objects will behave when falling in a vacuum, and it is also used in designing spacecraft and other objects that will experience freefall in a vacuum.

What factors affect terminal velocity in a vacuum?

The factors that affect terminal velocity in a vacuum include the mass and shape of the object, the acceleration due to gravity, and the density and drag coefficient of the object. Objects with a larger mass and a higher drag coefficient will have a higher terminal velocity, while objects with a lower density and a lower drag coefficient will have a lower terminal velocity.

Is terminal velocity in a vacuum the same for all objects?

No, terminal velocity in a vacuum will vary depending on the factors mentioned above. Objects with different masses, shapes, and drag coefficients will have different terminal velocities. However, in a perfect vacuum where there is no air resistance, all objects will eventually reach the same terminal velocity of 9.8 meters per second squared due to the acceleration of gravity.

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