Expert: Jayendra Upadhye - 3/17/2009

Question
QUESTION: hi - if time is relative to mass (as I have been taught, please correct me if I am wrong!) then everyone on the surface of the planet can use the same time scale due to the fact that they share a similar environment. Therefore if I move away from the surface of the earth (such as in a rocket) I will experience a different passing of time then someone who is still on the surface of the earth. If I am two floors up in a building though do I share the same time scale as someone who is on the surface of the earth?

ANSWER: Hi,
Yes and No!
Yes because for all practical purposes you will share his time, down to the last microsecond!

No because as you go higher up floors in a building, your rotational velocity increases by a tiny fraction. And so does your relativistic mass.
But how tiny is this tiny fraction?
you could use a calculator to find out.
It would be so small as to be a millionth of a microsecond!
[I am just being figurative, find exact fraction using time dilation speed / velocity formula).

What use would that be to you?

Sometimes science is good to know, but bad if you fail to see WHEN to apply it.

Secondly, time dilation has nothing to do with hieght from earth, but ones velocity as a proportion of C.

regards
Jayen

---------- FOLLOW-UP ----------

QUESTION: thanks! are you able to answer one more?

if my weight changes according to the planet that I am
on or in close approximation to is the same found with planets, so the earth
will weight more or less if put into orbit with a Star of appropriate relative size?

As in the time question, is it relative to the velocity rather than mass or with respect to weight is mass the determining factor. I can understand that this may be difficult as gravity has yet to be defined but was wondering if you could shed more light on this issue? In essence would earth weigh more if placed next to a star (or another body) of more mass or would the velocity of orbit be a more determining factor (I ask this as artificial gravity is currently achieved with rotational velocity)?

Answer
Hi,
1 - The weight or gravitational force on earth will vary as per the inverse square law.
Mutual pulling force between earth and any new star you place in place of the sun will be
f = G*(Mass of star)*(Mass of earth)/(square of the distance of separation).
Or
f/(Mass of earth) = G*(Mass of star)/(square of the distance of separation).

Or
Gravitational intensity g for earth (not self gravity g between objects close to earth and earth), g as between earth and the new star...
g = G*(Mass of star)/(square of the distance of separation).
Naturally for a given distance betwen the two cases, it will be greater if the new mass is larger than solar mass.


2 - Rest Mass is NOT important.
Velocity is.
As the velocity of the object becomes a significant percentage of that of light, its relativistic mass starts increasing. Consequently incrementing that velocity even a fraction requires a very large kinetic energy to be added! That energy has to be expended by something else (the driving power or force) in order for the body to axquire it. THAT is why travelling close to the speed of light is sooo difficult and expensive.

3 - Artificial gravity achieved by rotation is just an illusion.
It is an analogous force at best.
It is like simulating gravity on an iron piece using a magnet!
Not the real thing.
The walls of the revolving cylinder give you a centripetal reaction when your body attempts to move tangentially away in the rotating drum. The change in direction is percieved as inward acceleration.
That happens because, acceleration is defined as rate of change of velocity.
Velocity has two components or aspects speed and direction. Change only one, and keep the other constant, you will percieve that as acceleration. Keep spaeed same, and turn on a road, your body will stick tightly to the outer wall of the vehicle.
It doeanot mean there suddenly appeared a gravitating mass THAT side of the car!
It simply means you experienced first hand what "change in velocity" by direction means!!

regards
Jayen