If there are only two cars, then the difference is 20 m/s - 0 m/s.
The first car is sitting still and the second car is moving away at 20 m/s.
The Swing of a Pendulum
- Thread starter Motor Daddy
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If there are only two cars, then the difference is 20 m/s - 0 m/s.
The first car is sitting still and the second car is moving away at 20 m/s.
Motor Daddy
Valued Senior Member
How do you know one of the cars is sitting still? Sitting still compared to what?
He says that mass increases as an object accelerates and approuchs the speed of light so that it cannot do so unless it has infinity energy. This is the type of nonsensical thing I would expect from a Ph.D. (they should all be fired for letting this go on for 100 years) I have heard this excuss before in the classroom. The problem with it is that you would have to assume the observer at rest is the absolute frame or at absolute rest. The ship would have to be seen as traveling 99.99% the speed of light from an observer at rest in order to determine this. So then what if you took away the observer at rest and then the ship traveling at 99.99% the speed of light said that he was then at rest because he was traveling at a constant speed? He says his speed is 0% the speed of light and then increases his speed by 1m/s. The ship isn't going to hit an invisable wall because some observer could have been traveling 99.99% relative to him. So then it is saying that his constant speed that is close to the speed of light actually is not the same as being at rest, and places restrictions on it moving from rest or a high constant speed. So then they assume there is no absolute frame of reference but then prove that nothing can travel the speed of light by incorperating one. Go figure?
Sitting still compared to itself. The guy doing the measuring is sitting in the first car and says 'I'm sitting still and that other car is moving away at 20 m/s". Or, if he preferred, he could say 'that other car is sitting still and I'm moving away from it at 20 m/s.
It's all (and I know this is the part you reject) relative.
Motor Daddy
Valued Senior Member
That's ridiculous! Why would you try to measure your velocity compared to yourself?
You don't measure your velocity compared to yourself, you measure the velocity of the other car in relation to yourself.
Motor Daddy
Valued Senior Member
I already said the relative velocity was 20 m/s. I asked you what the velocities were and you said 20 m/s and 0 m/s. How do you know those velocities?
It is one difference of velocity. Delta. It's one number.
There is no way to tell what the two velocities are if they are the only objects in that universe. Only the difference between them. To give them a velocity outside of what their differences are would need introduction of a third party.
There is no way to tell what the two velocities are if they are the only objects in that universe. Only the difference between them. To give them a velocity outside of what their differences are would need introduction of a third party.
If the observer measuring the relative velocity is in an inertial framework, he may consider himself to be stationary, thus his velocity is 0.
All measurements of velocity are made relative to the measurer.
But increasing his speed by 1m/s would then put him over the speed of light from the other frame of reference. So then traveling at a constant speed relative to another object at 99.99% the speed of light wouldn't be the same as starting off from a position of being at rest. How could you say that one relative speed could be harder to attain than another speed when we have no idea what speed we are actually traveling? Say an object is traveling half the speed of light relative to you, you then determine that his mass increase slows him down from trying to accelerate. But what another guy says he is only traveling a quarter of the speed of light? Is he really traveling a half or a quarter of the speed of light? Then to which observer does the actual mass increase apply to him? There is no way to know, you cannot assign one of the observers an absolute frame that says his mass increases by this much because he is traveling that fast relative to that frame. This is because if they are all traveling at a constant speed then they are all equally right in saying they are the ones that are actually at rest. If the mass increased relative to just one of these frames then they would know that he was the one that was actually at rest.
Motor Daddy
Valued Senior Member
That is the relative velocity, which is one velocity. Saying "one car is traveling 20 m/s faster than the other" means there is two separate velocities. What are the two velocities and what are those velocities relative to?
It doesn't matter. And not known.
Car A goes 100 m/s, car B goes 80 m/s. They have the same viewpoint of each other as if car A goes 20 m/s and car B goes 0 m/s. The only way you know the difference is if you are basing their movement on a third point, ie the road. If it's just them and no other object, there is no way to tell.
It's 1 m/s in his frame of reference (and in his frame that's as fast as he's going,) but in the other frame of reference his increase is only a miniscule fraction of 1 m/s, due to length contraction and time dilation. From the other frame of reference, he will never attain the 1 m/s increase which would reach c. To be able to do so would, as AN said, require an infinite amount of energy
Motor Daddy
Valued Senior Member
So all you know is that the relative velocity is 20 m/s. That could mean that each rocket is traveling away from each other at the same rate (10 m/s), or that each rocket is traveling in the same direction at either 80/60, 29/9, 21/1.
So you have no basis for claiming that one rocket is traveling 20 m/s faster, since they could actually be traveling in opposite directions at 10 m/s each, 20 m/s relative velocity between them.
So then if there was an observer traveling at a constant speed close to the speed of light, it would take an infinite amount of energy for AN to put down his booze and get up off of the coach away from the T.V. so that he could approve my post I replied to him in my new thread I just started? I think it would only take infinite amount of energy relative to that observer, if they did observe it to have infinite mass, but black holes can have a velocity. They have infinite mass and still move around, go figure.
Motor Daddy
Valued Senior Member
Right, and that one velocity is not more or less than something that doesn't exist. A relative velocity is not two velocities it's one, so you can't have a faster and slower.