Main Question or Discussion Point
I am not really sure I have the concept of an inertial reference frame down, can anyone help me?
Ok I have a few questions. First you say that an inertial reference frame is one that is not accelerating. Is that a necessary and sufficient condition for a reference frame to be inertial, or is that just a necessary condition.Originally posted by HallsofIvy
More simply, an inertial frame is one that is not accelerating.
Velocity is "relative"- always measured with respect to something that is taken to be stationary. Acceleration is not relative so asserting that a frame of reference is or is not accelerating can be done independently of other frames.
Of course, in general relativity it is shown that such tests of acceleration depend on effects that could be attributed to forces such as gravity so the idea of an inertial frame becomes blurred in general relativity.
I disagree. You can always tell that you are accelerating no matter how something else is moving relative to you. Acceleration can be defined dynamically. (a=f/m) If I am moving at a constant V and I see a ship accelerating toward me, I can't say it's relative because I know I'm not accelerating.Tempest: Consider a free floating body in space, say a spaceship. The engines are off, and you release your apple. The apple floats. From that simple observation, you know the net force on the ship is zero, from which you conclude that the ship is not accelerating. Now consider another person in another ship which has its engines on, and is accelerating as it passes by you. You see it moving faster and faster, and suppose somehow you measure its rate of acceleration as 9.8 meters per square seconds. Now, in a reference frame whose origin is the center of mass of the rocket, you are accelerating at a rate of 9.8 meters per second. Hence, acceleration is relative. What isn't relative is force.
How is it that you don't fully understand the concept of an inertial reference frame and yet you are able to find errors in General Relativity?Tempest: I am not really sure I have the concept of an inertial reference frame down, can anyone help me?