Kinetic Energy | Earth Satellite vs. Truck: Same Ref Frame?

[SarahM]

Is the comparison of the kinetic energy of a satellite in orbit around the Earth to that of a truck traveling down a road realistic? Are they in the same reference frame?

 

[Andrew Mason]

Is the comparison of the kinetic energy of a satellite in orbit around the Earth to that of a truck traveling down a road realistic? Are they in the same reference frame?

It depends on how fast the truck is moving.

They are not in the same reference frame. They are both in an accelerating reference frame since they are both moving in a circle around the earth.

AM

 

[Tide]

That's actually an interesting question! Consider the situation when the truck is traveling down the road at 60 mph while the satellite is in geostationary orbit and you're observing from some comfortable perch that is fixed with respect to the Earth's surface. The satellite has no kinetic energy while the truck has quite a bit.

Clearly, there is something amiss with the comparison. To compare their kinetic energies properly you should use the same reference frame but the problem here is that the obvious reference frame (connected to the Earth's surface) is a rotating frame. Going to a nonrotating reference frame gives a very different picture.

 

[SarahM]

Well the truck has a velocity of 0.0289km/s and a K.E of 0.844 kgkm^2/s^2 and the satellite a tangential velocity of 7.473 km/s and a K.E of 279249 kgkm^2/s^2.
I was trying to compare the two K.E values but wasnt sure if it was realistic to do so.

 

[Tide]

It is realistic only in the sense of giving you some appreciation of the magnitudes.

Incidentally, energy is usually expressed in Joules = kg m/s^2 so the truck has 844,000 Joules of KE while the satellite has 2.79 x 10^11 Joules of KE.