Motion in Outer Space

[Luna]

Please, humor me here. A is car is moving through space at a constant rate of 50 mph by accelration on the gas pedal. You the remove your foot from the gas pedal. Does it continue to move at about a constant rate if acted on by minimal outside forces? And if it does continue at a constant rate with out the application of the gas pedal, what would happen once the force of the gas pedal is reapplied to 50 mph. Would the car then go faster, slower, or the same rate?

[mooeypoo]

Please, humor me here. A is car is moving through space at a constant rate of 50 mph by accelration on the gas pedal. You the remove your foot from the gas pedal. Does it continue to move at about a constant rate if acted on by minimal outside forces? And if it does continue at a constant rate with out the application of the gas pedal, what would happen once the force of the gas pedal is reapplied to 50 mph. Would the car then go faster, slower, or the same rate?

 

I am not sure I understand. First, "mph" is velocity and not acceleration, so the "acceleration on the gas pedal" is unclear here.

 

Second, the gas pedal moves the WHEELS faster, which relies on traction with the ground -- that's why cars slip when there's dark ice, for instance -- so pressing the gas pedal in space will do you no good. You need some form of push. Using Newton's third law fits here so you can throw stuff off the rear end or shoot a projectile, and get the reactionary force backwards to "push" the car.

 

Similarly, when you stop the gas pedal, it will do nothing at all.

 

 

However, if I understand your question correctly, then let me try and reframe it; if you use acceleration initially (by however means), the car will accelerate to, say, 50mph. When you stop the acceleration, the velocity will remain constant (lacking external forces). It will not slow down, because slowing down is also an acceleration ("Deceleration)" which requires a force.

 

Hope that helped,

~mooey

[swansont]

Second, the gas pedal moves the WHEELS faster, which relies on traction with the ground -- that's why cars slip when there's dark ice, for instance -- so pressing the gas pedal in space will do you no good.

 

It would tend to rotate you, though. There a scene in The Incredibles that depicts this reasonably accurately, though they were merely airborne.

[SMF]

How about the exhaust, there should be a little thrust from this.

[Airbrush]

Once you accelerate, but whatever means, to any speed in outer space, you will continue at that speed indefinitely, until you crash into something.

 

The rarified atoms in outer space will very slightly slow you down with a tiny amount of friction, but the stopping distance will be very, very long.

 

So how do you dodge a bullet on your way to another star traveling at 10%C?

Edited April 21, 2011 by Airbrush

[Luna]

Once you accelerate, but whatever means, to any speed in outer space, you will continue at that speed indefinitely, until you crash into something.

 

The rarified atoms in outer space will very slightly slow you down with a tiny amount of friction, but the stopping distance will be very, very long.

 

So how do you dodge a bullet on your way to another star traveling at 10%C?

 

 

So if an object begin accelerating by propulsion, even after the propulsion is stopped, it would continue at that rate. So if the same force of that propulsion was added once agian, would object's speed then double?

Edited May 9, 2011 by Luna

[Realitycheck]

It depends on the rate of thrust, possibly not.

[Schrödinger's hat]

So if an object begin accelerating by propulsion, even after the propulsion is stopped, it would continue at that rate.

It would continue at the same velocity. When the propulsion stops, acceleration goes to 0. Acceleration measures how quickly velocity changes so time is a factor as well.

So if the same force of that propulsion was added once agian, would object's speed then double?

If your propulsion was turned back on, acceleration would go back to it's previous value, so the speed (velocity) would start increasing again.

You'd have to leave your engine on for the same amount of time it was on previously to double your speed.

 

Play asteroids for a little while. Note that when you hold down the up key you are accelerating, when you release it you are not.

[Spyman]

So if an object begin accelerating by propulsion, even after the propulsion is stopped, it would continue at that rate. So if the same force of that propulsion was added once agian, would object's speed then double?

Inertia keeps objects moving when no force is acting upon them, a force is therefore needed to either slow them down or speed them up. The amplitude of a force and the time it is acting on the object determines what speed it will end up with.

 

Inertia is the resistance of any physical object to a change in its state of motion or rest, or the tendency of an object to resist any change in its motion. It is proportional to an object's mass. The principle of inertia is one of the fundamental principles of classical physics which are used to describe the motion of matter and how it is affected by applied forces. Inertia comes from the Latin word, iners, meaning idle, or lazy. Isaac Newton defined inertia in Definition 3 of his Philosophiæ Naturalis Principia Mathematica, which states:

 

• The vis insita, or innate force of matter, is a power of resisting by which every body, as much as in it lies, endeavours to preserve its present state, whether it be of rest or of moving uniformly forward in a straight line.
  

 

In common usage the term "inertia" may refer to an object's "amount of resistance to change in velocity" (which is quantified by its mass), or sometimes to its momentum, depending on the context. The term "inertia" is more properly understood as shorthand for "the principle of inertia" as described by Newton in his First Law of Motion; that an object not subject to any net external force moves at a constant velocity. Thus an object will continue moving at its current velocity until some force causes its speed or direction to change. An object that is not in motion (velocity = zero) will remain at rest until some force causes it to move.

 

On the surface of the Earth inertia is often masked by the effects of friction and gravity, both of which tend to decrease the speed of moving objects (commonly to the point of rest). This misled classical theorists such as Aristotle, who believed that objects would move only as long as force was applied to them.

http://en.wikipedia.org/wiki/Inertia

Edited May 10, 2011 by Spyman

[Leader Bee]

 

 

The rarified atoms in outer space will very slightly slow you down with a tiny amount of friction, but the stopping distance will be very, very long.

 

 

What about radiation pressure, or is that the same thing?

[Spyman]

What about radiation pressure, or is that the same thing?

Radiation pressure is electromagnetic and not from massive particles, but the CMBR would exert a very tiny force on a slow moving spacecraft.

Edited May 18, 2011 by Spyman

[Ophiolite]

If your propulsion was turned back on, acceleration would go back to it's previous value, so the speed (velocity) would start increasing again.

You'd have to leave your engine on for the same amount of time it was on previously to double your speed.

This is wrong. You are neglecting the reduction in fuel between the first phase of acceleration and the second. Since there is less mass to accelerate then with the same applied force the speed will be doubled in less than half the time.