Special Relativity Questions (1 Viewer)

[QZP]

Hi, I need help understanding special relativity.

Argument: An object approaching the speed of light will increase in mass. Thus, additional energy is required to speed up the object and as its mass approaches infinitely, the energy required approaches infinite. Hence, the object cannot reach the speed of light.
My counter: The effects of time dilation are apparent to only a stationary observer. The object is not physically gaining mass in its rest frame (ignore E = mc^2). Thus, its mass will not increase and it can approach the speed of light.

Another question: I observe length contraction for an object approaching from rest to relativistic speeds, when it returns to be stationary, does it go back to its original length?

Thanks in advance!

 

[CptSpauld1ng]

The rest mass of an object does not increase with its velocity, but in order to increase its velocity you must give the object kinetic energy increasing the total energy the object. This amount of energy is the same for both reference frames. The increase in energy of an object results in an increase in relativistic mass as mass IS energy. You cant ignore this mass-energy equivalency as it is really the central idea and basis of of special relativity.

For the other question, the relativistic length of an object is its apparent length to another observer caused by its velocity.The object (according to itself) is not actually gaining size, it just appears to for other reference frames. So if an object has a true length of one meter and an external observer views it as having a length of two meters, the actual size hasn't increased, it just appears to for the observer. So after an object returns to stationary its length will be the same as if it was being observed by someone moving with the object. Its length never TRUELY changes, just appears to change to other observer.

 

[QZP]

The rest mass of an object does not increase with its velocity, but in order to increase its velocity you must give the object kinetic energy increasing the total energy the object. This amount of energy is the same for both reference frames. The increase in energy of an object results in an increase in relativistic mass as mass IS energy. You cant ignore this mass-energy equivalency as it is really the central idea and basis of of special relativity.

For the other question, the relativistic length of an object is its apparent length to another observer caused by its velocity.The object (according to itself) is not actually gaining size, it just appears to for other reference frames. So if an object has a true length of one meter and an external observer views it as having a length of two meters, the actual size hasn't increased, it just appears to for the observer. So after an object returns to stationary its length will be the same as if it was being observed by someone moving with the object. Its length never TRUELY changes, just appears to change to other observer.

For the first one, the argument that an object can never reach the speed of light is based purely off of mass dilation (no textbook mentions mass energy equivalence; hence why i said ignore it). Also, the energy input is not consistent in both frames (explicitly said by my teacher who has a phd in phys). I already clarified this question today after school with the same teacher, but you can still argue your understanding and ill try to counter it for discussion purposes.

For the second one, that's my understanding too

 

[IR]

The rest mass of an object does not increase with its velocity, but in order to increase its velocity you must give the object kinetic energy increasing the total energy the object. This amount of energy is the same for both reference frames. The increase in energy of an object results in an increase in relativistic mass as mass IS energy. You cant ignore this mass-energy equivalency as it is really the central idea and basis of of special relativity.

For the other question, the relativistic length of an object is its apparent length to another observer caused by its velocity.The object (according to itself) is not actually gaining size, it just appears to for other reference frames. So if an object has a true length of one meter and an external observer views it as having a length of two meters, the actual size hasn't increased, it just appears to for the observer. So after an object returns to stationary its length will be the same as if it was being observed by someone moving with the object. Its length never TRUELY changes, just appears to change to other observer.

w0t, if e=mc^2 + 1/2 mv^2, and that the increase in energy is from the increase in relativistic mass to external observer, but the relativistic mass in both frames is different, hence you might be contradicting yourself on the energy part? Pretty sure my bolded part is based on rest mass and the not bolded KE part is based on relativistic.