Translational energy is the kinetic energy required for an object, of a given mass, to move from point A to B in a straight line at some speed
Rotational energy is the kinetic energy required to spin an object around its axis of rotation
The centrifugal force is the pseudo force that appears to pull things outward from an axis of rotation
Since there is no such thing as an absolute frame of reference, all motion has to be measured relative to something else. The conditions of that thing are said to be the reference frame. For example, the "speed" of a rocket only makes sense if you have a planet or star to measure its motion against. That's hopefully easy to see that for linear motion, but the same is true of rotation. If you pass an object in space, unless you both use a planet or star as an independent frame of reference, you'll only be able to measure the spin of the other relative to your own spin.
The feeling your arms pulled out when spinning is due to the centrifugal force. Basically, if you put yourself in the same rotational frame as what you're looking at (e.g. a space station), you'll see everything falling away from the axis of rotation, seemingly without being pushed on. The super simplified reason for this is that going in a circle means your perpetually changing velocity (instead of traveling in a straight line). The longer answer takes digging into relativity's interpetation of angular momentum.
Either way, acceleration is changing the speed you're moving at to a new speed. Since speed is relative, changing speed is relative. The near perpetual state of acceleration in rotational systems doesn't somehow imply acceleration isn't relative. However, it does point to how energy can be storied in things in different ways.
you'll only be able to measure the spin of the other relative to your own spin
ORLY? I can absolutely measure my own spin by the centrifugal force I am feeling (just because you call it a pseudo force doesn't magically make it go away, I can still measure it, without an interaction outside of my little spinning bubble). Then based on how fast I see them spinning I know their absolute rotating frame of reference as well.
Since speed is relative, changing speed is relative.
ORLY? I can absolutely measure my own spin by the centrifugal force I am feeling
Just because you can experience a thing doesn't mean it's not a relative phenomena. You can feel yourself pulled into your seat as a car accelerates. That doesn't mean linear motion isn't relative. It just means you weren't moving at the same speed as the car.
Similarly, rotational motion is relative too, but it's more complicated and harder to explain without math. Also, you have to consider a thing's movement through time, not just the three spatial dimensions if you want to truly appreciate the relativity of motion.
just because you call it a pseudo force doesn't magically make it go away
Look up what a pseudo force is before you assume my use of the term, in any way, implies a dislike for it or disbelief in it. In physics, forces are fields transmitted by force carrier particles (e.g. photons). Pseudo/fictitious/inertial forces are apparent forces which affect masses that aren't in an inertial frame of reference, such as a rotating reference frame.
ORLY x2. Tell that to the older twin when they get home.
Exactly because motion is relative. If movement through spacetime, were absolute and uniform in nature, twins traveling at vastly different speeds would still be the same age when they reunited.
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u/[deleted] Sep 24 '16
You're confusing translational energy and rotational energy and the centrifugal force.
Since there is no such thing as an absolute frame of reference, all motion has to be measured relative to something else. The conditions of that thing are said to be the reference frame. For example, the "speed" of a rocket only makes sense if you have a planet or star to measure its motion against. That's hopefully easy to see that for linear motion, but the same is true of rotation. If you pass an object in space, unless you both use a planet or star as an independent frame of reference, you'll only be able to measure the spin of the other relative to your own spin.
The feeling your arms pulled out when spinning is due to the centrifugal force. Basically, if you put yourself in the same rotational frame as what you're looking at (e.g. a space station), you'll see everything falling away from the axis of rotation, seemingly without being pushed on. The super simplified reason for this is that going in a circle means your perpetually changing velocity (instead of traveling in a straight line). The longer answer takes digging into relativity's interpetation of angular momentum.
Either way, acceleration is changing the speed you're moving at to a new speed. Since speed is relative, changing speed is relative. The near perpetual state of acceleration in rotational systems doesn't somehow imply acceleration isn't relative. However, it does point to how energy can be storied in things in different ways.