Please help (1 Viewer)

[bboyelement]

Obital Decay
im really confused right now... in the jacaranda book it says"as a satellite slows down it loses altitude ...." which doesnt make sense at all ... think about it say if you slow down you would increase the period (say around the Earth) which is true because it would take longer to complete a revolution around the earth ... true?
v=2(pi)r/T ... hence if T increases r would have to increase

you could look at another equation v=root[Gm/r] if you decrease v (orbital velocity) you would have to incease r ....

or you could look at the keplers third law of motion r^3/T^2 = k(constant) ... so if you increase T then you would have to increase r

unless increasing r means losing altitude ... i got no idea...

ok another question ... in Quanta to Quarks you learn that light is a particle and wave duality... rite?
if you apply the equation of mass dilation since the its the speed of light then the mass will move towards infinity hence when it strike us ... shouldnt we be dead ... also that fact that it is constant velocity its in an inertial frame of reference which should be true ... im really confused thanks

 

[zeropoint]

Obital Decay
im really confused right now... in the jacaranda book it says"as a satellite slows down it loses altitude ...." which doesnt make sense at all ... think about it say if you slow down you would increase the period (say around the Earth) which is true because it would take longer to complete a revolution around the earth ... true?
v=2(pi)r/T ... hence if T increases r would have to increase

you could look at another equation v=root[Gm/r] if you decrease v (orbital velocity) you would have to incease r ....

or you could look at the keplers third law of motion r^3/T^2 = k(constant) ... so if you increase T then you would have to increase r

unless increasing r means losing altitude ... i got no idea...

Your argument doesn't follow using the equation v = (2 pi r)/T. The speed of the object is not some kind of conserved quantity as you suggest.

As for v=root[Gm/r]. You cannot use this equation in this circumstance because it is formulated under a different set of assumptions. Namely, that the net force acting on the object is the gravitational force, which is certainly not true for an object undergoing orbital decay. The same argument applies for Kepler's law.

An object undergoing orbital decay experiences frictional forces from the atmosphere which perform negative work on it. Can you explain why this leads to a reduction in altitude based on energy considerations? (Hint: what is the expression for the total energy? What is the effect of friction?)

ok another question ... in Quanta to Quarks you learn that light is a particle and wave duality... rite?
if you apply the equation of mass dilation since the its the speed of light then the mass will move towards infinity hence when it strike us ... shouldnt we be dead ...

Hmm, not really. What you learn is that light can exhibit both wave and particle-like properties. Whether it behaves more like a particle or more like a wave is related to its frequency. In any case, the photon is a massless particle meaning that the relativistic equation of mass increase is not applicable here.

also that fact that it is constant velocity its in an inertial frame of reference which should be true ... im really confused thanks

I'm sorry but Ihave no idea what you're talking about here. Can you rephrase that?

 

[alcalder]

I think the point being made about the speed of light in an inertial frame of reference refers to the observed phenomenon that light has a constant velocity no matter what frame of reference it is in.

The velocity of light is, seemingly, always c, even if it is placed on a train moving at velocity =v. Ie the speed of light does not suddenly change to v+c.

Is that what you mean?

c seems to be the upper limit of the speed of light. Putting a light source on the train will alter the frequency you see (from the front, blue shift - or back, red shift) but not the speed. Light is acting as a wave in this case and not a particle.

 

[bboyelement]

I think the point being made about the speed of light in an inertial frame of reference refers to the observed phenomenon that light has a constant velocity no matter what frame of reference it is in.

The velocity of light is, seemingly, always c, even if it is placed on a train moving at velocity =v. Ie the speed of light does not suddenly change to v+c.

Is that what you mean?

c seems to be the upper limit of the speed of light. Putting a light source on the train will alter the frequency you see (from the front, blue shift - or back, red shift) but not the speed. Light is acting as a wave in this case and not a particle.

yes thats what i meant ... because its a constant velocity the principle of relativity still holds in that circumstance ... but thanks for clearing that up
about the orbital decay the total mechanical energy is E=-1/2(GmM/r) according to JAcaranda which is suppose to be the sum of the kinetic energy and potential energy ... this does make sense that if you lose kinetic energy then you decrease r but then again when do you know which one to use because its so weird in some circumstances this equation works in some its not valid ...

 

[zeropoint]

E = - GM m / 2r is the expression for the mechanical energy of the system as you said. It is _always_ true for any object in orbit (physics is not selective). What may not be true is that the mechanical energy is conserved. Forces like friction can subtract energy from E = - GM m / 2r and other forces like rocket propulsion may add to it. Does that help?

 

[Irskin]

Think about the question logically; a satellite in orbit must have:
gravitational force = centripetal force. Now If the velocity of the satellite dereases then the gravitational force will become larger than the centripital force and therefore the satellite will be pulled in towards the earth, losing altitude. It is also important to note that satellites in low earth orbit are not pulled in towards earth because gravity is too strong, but because it collides with many particles in the upper atmosphere (friction).