Space Questions (not related to hsc but i am curious) (1 Viewer)

[Miroku]

Three questions
1:Speed of light is always constant.
Q:What happens when it is affected by gravity? (eg Light is pulled into black hole. What would happen if you fire light upward on surface of black hole?)

2:Galileo's "Principle of relativity" states that all steady motion is
relative and cannot be detected without reference to an outside point.
Q:What happens if you measure your mass? If you are moving with
high uniform velocity wouldn't your mass increase relative to your rest
mass?

3:It is said that it is impossible to achieve speed of light because of mass
dillation.
Q:Mass dilation is the increase in the mass of an object as measured from any other inertial reference frame in relative motion to the first. That means if you are travelling inside a rocket travelling at speed of light and measure the mass of the rocket, the mass of the rocket would be the same as the rest mass. The mass only increase when measured by outside observer. This means rocket's mass does not increase.

Even if the mass of the rocket increases, then so does the hot gases expelled through out the nozzle of the rocket. The rocket accelerates by forcing large volume of gases backward behind it. This means if the rocket provide cosntant thrust, then it would continue to accerelate at same rate.

 

[airie]

1:Speed of light is always constant.
Q:What happens when it is affected by gravity? (eg Light is pulled into black hole. What would happen if you fire light upward on surface of black hole?)

Light is not exactly "pulled into a black hole" in this case. Black holes appear black since their gravity is so strong that even light speed cannot overcome the escape velocity. So light still travels at c, it's just that it doesn't ever reach you since even c is insufficient to overcome the gravity of the black hole.

2:Galileo's "Principle of relativity" states that all steady motion is
relative and cannot be detected without reference to an outside point.
Q:What happens if you measure your mass? If you are moving with
high uniform velocity wouldn't your mass increase relative to your rest
mass?

Since you're in your own frame of reference, the mass you measure will be your rest mass.

3:It is said that it is impossible to achieve speed of light because of mass dillation.
Q:Mass dilation is the increase in the mass of an object as measured from any other inertial reference frame in relative motion to the first. That means if you are travelling inside a rocket travelling at speed of light and measure the mass of the rocket, the mass of the rocket would be the same as the rest mass. The mass only increase when measured by outside observer. This means rocket's mass does not increase.

Even if the mass of the rocket increases, then so does the hot gases expelled through out the nozzle of the rocket. The rocket accelerates by forcing large volume of gases backward behind it. This means if the rocket provide cosntant thrust, then it would continue to accerelate at same rate.

For the first part, the acceleration is done with respect to the reference frame of the Earth, so the mass *does* increase in the Earth frame. (Remember the rocket's not accelerating with respect to its own reference frame )

And for the second part, again, consider the reference frames. The energy released from burning an amount of fuel is the same; such energy needs to cater for the acceleration of the rocket with respect to earth, which requires increasing energy due to its increasing mass as observed from earth.

(Btw, acceleration is involved here so *maybe* you should read up on General Relativity yourself too. I don't know it well enough to use it to explain things )

 

[Miroku]

Light is not exactly "pulled into a black hole" in this case. Black holes appear black since their gravity is so strong that even light speed cannot overcome the escape velocity. So light still travels at c, it's just that it doesn't ever reach you since even c is insufficient to overcome the gravity of the black hole.

aa

 

[Miroku]

According to Galileo, the motion of projectile consists of two separate and independent motions superimposed upon each other. The first is vertical, which is accerelation due to gravity, and the second is a horizontal motion, which is constant.

If we consider light as a projectile, when it passes near blackhole parallel to its surface then it will experience the force of gravity. Then its horizontal velocity will always be 'c' while experiencing vertical accereration. Using the trigonometry, wouldn't the combined velocity of light would be greater than 'c'?

 

[airie]

According to Galileo, the motion of projectile consists of two separate and independent motions superimposed upon each other. The first is vertical, which is accerelation due to gravity, and the second is a horizontal motion, which is constant.

If we consider light as a projectile, when it passes near blackhole parallel to its surface then it will experience the force of gravity. Then its horizontal velocity will always be 'c' while experiencing vertical accereration. Using the trigonometry, wouldn't the combined velocity of light would be greater than 'c'?

OK, the process is, normally you see objects cos light is reflected off them. But in the case of black holes, light is shone on them alright, but it doesn't get reflected to you cos its speed is still too slow to overcome black hole's gravity ie. c is less than the escape velocity.

And on the constancy of light speed, I said, go read up on General Relativity. That's the one considering acceleration (including gravity) and all. You realise that light travels in curves, not straight lines, in a gravitational field; therefore a constant c is only limited to Special Relativity, which considers inertial frames alone and ignores gravity.

Did that answer your question? ... Actually, what's your question again? (I get lost quite easily...)

EDIT: If you were thinking an apparently greater-than-c speed of light might let it overcome black hole's gravity...ok, "using trigonometry", what direction is the velocity?

 

[Miroku]

Does that mean speed of light can exeed 'c' in General Relativity?

Thanks for answering my questions.

You know a lot about space.

 

[Skedd]

Did that answer your question? ... Actually, what's your question again? (I get lost quite easily...)

hehe, its funny cause you do/have done physics... the subject that is one of the easiest to get lost in

well, for me anyway...

but what you are saying makes sense to me! didnt know that before, thanks

 

[xds123]

in order to answer your first question you must forget about Newtonian or classical physics, which are increasingly being shown to be wrong, e.g. Newtons laws do not account for anomalies in Mercury's orbit. instead you must look to Einstein's description of gravity which is gravity is a curvature in space time. in other words mass curves spacetime. it is easier to think of space time as being a grid on a rubber sheet, when you place a marble on the sheet the mass causes the sheet to be indented and for the gridlines to curve. the light continues in a straightline along the gridlines and at a constant velocity but since the lines themselves have been 'warped' the path appears curved. experiments conducted in 1919 showed this to be true when observers viewed the 'curving' of light due to the Sun during a solar eclipse see http://en.wikipedia.org/wiki/Solar_eclipse#1919_observations



http://en.wikipedia.org/wiki/Gravity#General_relativity

 

[alcalder]

Actually, the constancy of the speed of light is a matter of contention. There are proponents who argue that the speed of light is slowing down.

But for Year 12 Physics purposes, it is constant.

Just because you are taught something in Year 12 Physics (or Uni Physics) doesn't mean you can't challenge or change it because we don't "know" how everything works, we just think we do.