how many pounds of constant thrusts does it take to push a ship to near the speed of light if a craft is?

Question

weightless. it seems like 100 pounds of constant thrust should get you up to a close speed if it is constant to the point of destonation, but how long?

Answer 1

This is one of the principles of relativity. Firstly we must classify weightless - as in, no gravity around to give a mass weight. As in space. However, the craft is never "weightless" when you accelerate toward the speed of light. Einstein's equation that everyone knows says energy = mass * speed of light, right? That also implies that as a mass approaches the speed of light, its mass increases parabolically. So in otherwords, even if you have no weight, you still have mass. And lets really go out there and say you have nearly no, or no mass, perhaps your craft weighs 1/1,000,000,000 of a gram - as you approach the speed of light your mass drastically increases, ridiculously so. At 90% the speed of light you might weigh a gram. At 95% who knows, 1000 kg? Even subatomic particles cannot go the speed of light unless they have no mass at all (like photons) and even then they require nuclear (atomic level) energies to do it. Thus you would need to constantly increase the amount of thrust to reach light speed until the energy requred became infinity. Even if you had infinite thrust, you couldn't get any closer than a certain fraction of lightspeed because as you got closer and closer, your mass too would become infinity and you would be theoretically impossible to move any faster.

I'm paraphrasing, but I think the gist of the answer is "an infinite amount, for an infinite amount of time, would not get you to light speed - but you might get close. The bad news is even if you don't reach light speed, just being close to it would mean all your friends and family would be 10,000 years dead if you did it and came back after a year."

Answer 2

If it's weightless, any amount of constant thrust would get the job done.

However, even assuming a moderately small weight, what you need to consider is that, the faster an object moves, the greater its mass becomes, which in turn requires more and more thrust to keep accelerating. It's just one of those freaky things, but that's what keeps anything other than light from going the speed of light.

Answer 3

Alas, it's not as simple as that. I assume by 'weightless' you do not mean 'massless', since all tangible objects have mass.
Now, according to Newtonian mechanics, F = ma, where F is the force applied (the thrust), m is the mass of the spacecraft and a is the resultant acceleration. For the purposes of calculation, it is easier to use metric units, so, what is 100 lbs of thrust in Newtons? (Newtons being a standard metric force unit).
100 pounds is about 45 kg. 45 kgs of thrust = 45 kgs x earth gravity, g = 9,8 ms^-2.
45 x 9.8 = 441 kgms^-2 = 441 Newtons.
So, what acceleration will a spacecraft of mass 'm' undergo, upon application of 441 Newtons of thrust?
F = ma, so, a = F/m = [441/m] ms^-2

So, in order to calculate how long it takes to reach light speed, use the following equation:
v = u + at. v = final velocity, u = initial velocity, a = acceleration and t = time taken.
In this case, v = c (the speed of light), u = 0, a = [441/m].
So, by substitution,
c = 0 + [441/m]t
Rearrange and simplify:
t = cm/441.
c = 300,000,000 ms^-2 , so
t = 680,272m seconds. So, in principle, 100 lbs of thrust will take (680272 x m) seconds to accelerate mass 'm' from rest to light speed.

HOWEVER: Newtonian mechanics works alright at low speed, but has been superceded by Einstein's relativity theory. Unfortunately, as an object is accelerated towards the speed of light, its mass does not remain constant, but instead, bizarrely, begins to increase.
In fact, the mass of an object 'm' travelling at velocity 'v', is given by the following equation:

m = m(0)/[[1-(v^2/c^2)]^(1/2)], where m(0) is the mass of the object when it is at rest, m is its mass at velocity 'v' and 'c' is the velocity of light. If you feed numbers into this equation, you will see that the closer 'v' gets to 'c', the larger the value fro the mass 'm' becomes. in fact, at the speed of light, the object attains infinite mass. This is why it is regarded as impossible to attain or surpass light speed.
Obviously, if the mass is always increasing then the acceleration allowed by a given amount of thrust is always declining (because F = ma), so it would take, in reality, an infinite amount of time to reach the speed of light, using constant thrust.

Answer 4

Hi. You have to decelerate to stop at your destination, but in physics that still counts as acceleration. Any force applied to a massless 'thing' results in instant acceleration to the speed of light. If the spaceship has 100 pounds of mass then 100 pounds of thrust will result in a 1g acceleration. And, yes, it could get pretty close to c, but as a previous answer pointed out, it would take a long time.

Answer 5

In a rocket, you have to push the weight of the fuel you're going to use in the future, using the fuel you're using now. That means the that the most important thing for achieving high speed is the velocity of the exhaust. The best you can do is have an exhaust velocity that is the speed of light---in other words, a photon drive.

Answer 6

you will possibly see it going slower, as out of your vantage factor, you would be entitled to declare you at the instant are not moving on a similar time as the entertainment of the universe is going the different course at close to to the fee of sunshine. The dis-synchronization is with out doubt between the main weird element of relativity, and the twin's paradox is resolved by getting you ultimately slowing down or coming lower back after turning around. given which you changed your speed, then you switched over your referential, and then will might desire to agree that, on a similar time as the universe became as quickly as zooming via ability of on the 'out going' leg of your bypass lower back and forth, then you rather crancked up the speed to get closer the universe with the intention to return. The time dilation for this reason, is utilized to the universe at a modest price, and to you on your return holiday to an fairly severe degree. Of course, in case you go away Earth with a 0 relative %. and speed as much as close gentle speed, you're additionally changing referential each and every 2nd, so by this a while dilation is likewise relative to three buoy you have have been given dropped interior the lower back of on the way, as you develop your speed.

Answer 7

Sounds like you're talking about an ion drive. It can have the force of a piece of paper yet get a ship to very high speeds. Not near c yet though

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

Answer 8

100 lbs of thrust would do it but you need to do it for a LOONNNGGG time.