# Acceleration/Deceleration

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if accelerating an object adds mass because you have to apply energy to it, shouldn't decelerating an object also add energy to it? lets say you doubled the mass of a partical by accelerating it, wouldn't decelerating it double it again?

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there is no distinction between acceleration and decelleration, they are both acceleration.

your frame of reference will determine whether energy is added or subtracted from the object(in your frame of reference obv.).

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So the mass is never real from all perspectives?

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It's never the same from all perspectives, no.

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But is it real? If not then what is real? If everything depends on your perspective then is nothing real but your perspective?

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Mass, as it is usually defined, is unchanged by motion. Making it speed/frame dependent requires using an alternate definition.

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So going near the speed of light doesn't make a particle or space craft more massive?

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So going near the speed of light doesn't make a particle or space craft more massive?

No, it gives it more kinetic energy, which is frame dependent.

E^2 = p^2c^2 +m^2c^4

The equation reduces to E = mc^2 only for a particle at rest, i.e. in its own frame of reference. To rearrange that and define mass as E/c^2, and then apply it to a moving particle violates the conditions under which the equation was derived.

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So an object really doesn't become more massive as it's accelerated near the speed of light?

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The effects of relativity are very real and has been confirmed in all observations and experiments to date.

If you would be in a spaceship moving very fast relative me here on Earth, you would not only seem to be more massive, you would also look shorter and your clock would tick slower than mine. For you in the spaceship the effects would be reversed, everything in the spaceship including yourself would seem normal but when you look down on me, I would appear from your point of view to be more massive, shorter and that it is my clock that ticks slower. Two events, (A & B), at different locations might be seen as happening in different order from our vantage points, I can see that A happens before B, while you will see that B did happen before A.

For each and every observers point of view, in every possibly frame of reference, the values will be real, follow the laws of nature and can be used to calculate different outcomes.

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Your relativistic mass increases as velocity in a given rest frame increases.

The rest mass, which is normally referred to as just mass, does not change.

Discussing mass, when you mean relativistic mass is not good, it is perfectly acceptable and in most cases preferred to formulate special relativity with only a single static mass, identical to rest mass, which does not change.

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(...)

The rest mass, which is normally referred to as just mass, does not change.

(...)

In other words, nothing forbids you to accelerate, independently of your velocity. It is really easy to understand, because velocity is relative. Relative. Relative. (I have to say it 3 times like at church, to be sure the disciples hear the sermon).

What will another observator measure, from another FOR has absolutely no effect on you. This other fellow will measure your (relativistic) mass increase, but that is only a relative observation. Nothing bizarre will happen to you.

The only bizarre effect is that if (hypothetically) you pass the speed of light relatively to some observator, this other fellow will measure that you will not have pass SOL. And reversely, you also, measuring the same velocity from the other side, you will also measure that the other fellow's velocity relative to you is less than SOL: that is the reason why scientists say that it is impossible to go FTL. Not because something physically cuts your speed, as commonly believed, but because it is impossible to observe directly.

Amen.

Edited by michel123456
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The only bizarre effect is that if (hypothetically) you pass the speed of light relatively to some observator, this other fellow will measure that you will not have pass SOL. And reversely, you also, measuring the same velocity from the other side, you will also measure that the other fellow's velocity relative to you is less than SOL: that is the reason why scientists say that it is impossible to go FTL. Not because something physically cuts your speed, as commonly believed, but because it is impossible to observe directly.

I'm going to need a reference for this. i.e. that you can do it, and it's not that the energy diverges, but that it's because of observation.

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For each and every observers point of view, in every possibly frame of reference, the values will be real, follow the laws of nature and can be used to calculate different outcomes.

So in the twin paradox both with be young? If all frame of reference are real then not only is the mass real (eventually you or a particle should collapse into a black hole if you accelerate close enough to the speed of light) Both frames of reference should be time dilated permanently, no twin paradox?

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I beg you don't go into the twin paradox again.

Merged post follows:

Consecutive posts merged
I'm going to need a reference for this. i.e. that you can do it, and it's not that the energy diverges, but that it's because of observation.

The entire Theory of Relativity is based upon an axiom that comes from observation. SR & GR are theories of observation: they start from observation, they end to observation (as any decent Theory must do).

SR & Gr are absolutely right, correct. But they still are about observation.

If you decide to move, it will not change the physical behaviour of a galaxy light years away. Speed is relative.

Crudely, you can masturbate as long as you want, I will not feel orgasm.

And what you observe is not necesseraly what happens.

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The entire Theory of Relativity is based upon an axiom that comes from observation. SR & GR are theories of observation: they start from observation, they end to observation (as any decent Theory must do).

SR & Gr are absolutely right, correct. But they still are about observation.

If you decide to move, it will not change the physical behaviour of a galaxy light years away. Speed is relative.

Yes, speed is relative. Now back up your claim that superluminal speed is possible under relativity.

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For each and every observers point of view, in every possibly frame of reference, the values will be real, follow the laws of nature and can be used to calculate different outcomes.

So in the twin paradox both with be young? If all frame of reference are real then not only is the mass real (eventually you or a particle should collapse into a black hole if you accelerate close enough to the speed of light) Both frames of reference should be time dilated permanently, no twin paradox?

First let's assume that we have three spaceships approaching a common spacestation with different relative speeds. They will all three observe that the spacestations clock will tick with different rate than their own, but they will not be able to agre on how much.

Is the values on the spaceships clocks not real, is the only real value the common clock on the spacestation, or does the spacestation have four real times simultaneous, or maybe all values are unreal?

Well, as I understand relativity, they all measure real values which means that the relation between the object and the observer affects their readings. The environment for observers and the objects determines how different measurements will be scaled relative each other.

What is real in one environment might not be in another, but for an observer in a different state relative us the measurements are as real to him as our measurements are to us. We can use the theory of relativity to transfer observed values between different frames and predict what others will percieve.

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Now take the twin paradox, let's assume that they are not twins but triplets and the third is in a second spaceship that is bolted to the one used in the twin paradox. As such two of them make identical journeys and when observing each other their clocks ticks with the same speed, but their first sibling staying on Earth will disagre with their observations. When the first and the third sibling observe the second brother, which one of them will measure the real values?

To be fully able to resolve the twin paradox one must be able to distinguish between acceleration and speed, because according to relativity they affect observations differently. If two observers are moving with constant speed with respect to each other then both will measure the others clock to go slow an the situation is symmetrical, but if one is accelerating relative the other the situation will be different. Then they will still disagree on the time but the one accelerating will measure the others clock to be faster and the one not accelerating will measure the accelerated clock to be slower.

In the twin paradox the twin leaving in the spaceship must first accelerate when he takes off from Earth to reach a high speed, then he needs to accelerate again during the U-turn to be able to come back to Earth and then finally he needs to accelerate again to slow down and land on Earth. The difference in acceleration makes their relative journeys unsymmetrical and explains the difference in age.

If you put the twins on two identical spaceships that takes off in opposite directions with identical acceleration then they will measure different rates off time due to speed only and when they deccelerate to rendezvous the difference in time will decrease proportional with their relative speed towards zero. In this case they will not find the other to be either older or younger when they meet.

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If you would be standing on a weighting scale inside a spaceship accelerating with 9.8 m/s2 in the direction from your feet towards your head you would measure the same weight as you normally do here on Earth, independently of the spaceships speed. In your frame of reference you continue to weight as normal, thus no Black Hole.

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Spyman, I followed half your post, I think you 're right (the other half about twins doesn't interest me).

Yes, speed is relative. Now back up your claim that superluminal speed is possible under relativity.

Here is a spreadsheet not made by me, but by another member (nicknamed Jerrywickey) on another Forum. He is examining a spaceship leaving the Earth under constant acceleration 1g, and what happens for observers on Earth & on the spaceship.

No one (on the other Forum) was able (or interested) to check his numbers.

From the original OP

"250 days after leaving, the travelers perceive they have exceeded the speed of light (1). The travelers will be slightly more than 0.29 light years from Earth. 278 days will have passed on Earth; and an Earth bound observer measures the travelers speed at only 71% c

After 556 days pass on Earth, observers on Earth will measure the travelers speed as very near light speed. The travelers will be 1 light year from Earth at this time. Only 353 days will have passed for the travelers who are measuring their speed at what appears to them to be ever increasing multiples of light speed, hundreds and thousands of times the speed of light because time is passing more slowly for them, of course. Each second that passes for the travelers on day 353 increases the speed at which they perceive themselves exponentially.

They travel until they reach half the distance to their destination. No matter how far that distance is, the next star or the other side of the universe, they will reach that middle point sometime on day 353 or just hours into day 354, at which time they turn the thrust of the ship around to begin slowing down at 1 g. In another 353 days they will arrive at their destination.

556 days on Earth and at their destination will pass during the traveler's 353 day acceleration and another 556 days will pass during their 353 day deceleration, but any number of years, centuries or millennia will pass during the 353rd and 354th traveler day as they cruise through space at incrementally increasing relativistic speeds.

Of course while we have the nuclear power off the shelf and we have the ability to build such a space ship, even a single free atom in space striking the space ship at relativistic speeds would impart catastrophic energies which would destroy the space ship instantly.

But I was hoping someone might be able to check my numbers.

I am using SQR(1-v^2) as the relativistic transform and you will find the ship's speed from both the observer at rest and the ship's frame of reference on a second by second basis for each day at http://spreadsheets.google.com/ccc?key=0AkfQmC4TTWCQdGpUcXlYR0U2ckowal9aZW96TTRDVWc&hl=en#gid=0.

Jerry"

You can make a quick check looking at the chart inside the spreadsheet.

The interesting values are at the end of the spreadsheet.

There is no other way than checking by yourself. It is Relativity in application, not a new theory.

(1) the "perceive" is made by triangulation with some reference stars.

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The travelers do not perceive themselves moving faster than light. In the travelers' rest frame, the distance of the journey is shorter than it is in Earth's rest frame. You only get FTL results if you mix reference frames - time elapsed in travelers' rest frame, distance traveled in Earth's rest frame.

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Going through the explanation on that other forum, it's clear that he is mixing frames, just as Sisyphus predicted would be the case. The observer is measuring his speed using known distances measured while at rest. You have to use the distances measured while traveling, since they will be different from the rest measurements owing to length contraction.

I suspect nobody could check the numbers; I didn't see any equations in the spreadsheet.

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You can make a quick check looking at the chart inside the spreadsheet.

The interesting values are at the end of the spreadsheet.

There is no other way than checking by yourself. It is Relativity in application, not a new theory.

Just a point about this -- this isn't application. Application would be to send an actual ship and record the observation on a spreadsheet and then compare the numbers to the known theory.

What that spreadsheet does is uses the known mathematics to produce numbers. It can be wrong, or it can use wrong equations, or it can misunderstand the theory, and a whole slew of possibilities that would make these numbers plainly irrelevant.

That wouldn't happen if the ship was real and the spreadsheet was a recording of actual observation -- which would make it into a practical application of Relativity and not a theory.

~moo

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I suspect nobody could check the numbers; I didn't see any equations in the spreadsheet.

Equations show in the grey area labeled "formula" right above the A B C D columns, when you tick a number in the spreadsheet.

____________________

Sometimes, I feel tired with all this.

1.We all agree that speed is relative.

2.We all agree that a traveller won't see his own mass change, no matter what speed.

Of course because speed is relative.see (1)

What else do you want to understand that nothing can physically prevent the traveller from going faster?

Of course because "going faster" is relative. see (1)

What is wrong in this?

Am I totally out of logic or are you all completely stuck ?

Edited by michel123456
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Just a point about this -- this isn't application. Application would be to send an actual ship and record the observation on a spreadsheet and then compare the numbers to the known theory.

That would be experiment, not application. Application is just using the formulas for any purpose.

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Equations show in the grey area labeled "formula" right above the A B C D columns, when you tick a number in the spreadsheet.

None of the speed calculations I checked give a formula, other than unit conversions.

Sometimes, I feel tired with all this.

1.We all agree that speed is relative.

2.We all agree that a traveller won't see his own mass change, no matter what speed.

Of course because speed is relative.see (1)

What else do you want to understand that nothing can physically prevent the traveller from going faster?

Of course because "going faster" is relative. see (1)

What is wrong in this?

Am I totally out of logic or are you all completely stuck ?

I object to the phrase "nothing can physically prevent the traveller from going faster." What part of relativity permits this?

The energy of the rocket as measured by the observer at rest diverges as v approaches c. The rest frame observer will never see the rocket's speed exceed c. If an action is forbidden in one frame, it is forbidden in all frames. (Which is a useful tool, because most calculations are easier in some frames of reference, so checking violations of conservation of energy or momentum can be done in a convenient frame)

In the rocket frame, the length is contracted by gamma; the rocket observer measures a shorter length as the speed increases. The resulting speed calculation from that frame will never exceed c.

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That would be experiment, not application. Application is just using the formulas for any purpose.

Isn't 'application' hint that you 'applied' it?

Applied.. as opposed to theoretical....?

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