Because I'm Picky

(...and I apparently inhierited my dad's fondess for lecturing...)

Inertia is something objects have. It doesn't change unless the make-up of the object itself changes. Mass is a measurement of inertia.

A superpower that allows one to change an object's inertia would be very cool and very useful. I could make someone "light" enough that I could easily throw him or her, and I can make myself (or just parts of myself) "heavy" enough that my opponent would have a difficult time harming me. I could even start doing all sorts of cool things most people only get to do in zero g. The acrobatics I could do would be more useful and unique than my ability to use my powers as a substitute for super strength. Like Superman, I could be both impenetrable to bullets and able to leap tall building in a single bound - I would just find it more difficult to do both at the same time.

Momentum is also a quality that objects posses, but it is dependent upon both mass (inertia) and velocity. (p=m*v) Velocity is a vector, which means that it must include not only an amount (speed) but a direction. A change in velocity may consist of nothing more than a change in direction. A change in velocity will, of course, change momentum as well.

Kinetic energy is a kind of mechanical energy. Again, it is a quality used in describing objects. Like momentum, it relies on mass and velocity, but unlike momentum it relies on velocity more than mass. (KE=1/2*m*v*v)

A superpower that allows one to change an an object's kinetic energy would be rather like a superpower that allows one to change an object's momentum. Anyone can do that by applying force and affecting velocity. It's only a superpower if you can do it ten times better than normal humans. This is what Superman does - he uses super strength to change momentum and kinetic energy to a greater degree than a normal human could.

Being able to simply transfer kinetic energy from one object to another is only a superpower if you can do it without having to touch the object with anything else. Being able to play pool is not a superpower. If you are able to transfer more kinetic energy than a normal human would then your superpower is the ability to change an object's kinetic energy to an abnormal degree, not the ability to "transfer" kinetic energy. If you are able to store kinetic energy and transfer it at will, then that is your superpower. It has very little to do with inertia and claiming that your superpower is the ability to transfer kinetic energy is like saying Nighcrawler's superpower is the ability to travel from one place to another.

Sorry for the physics lesson.

I just read Jake's excellent snark on Inertia (via When Fangirls Attack) and I'm not going to blame anyone in particular (I have no idea if the fault lies with the people who created Inertia or with the people describing her powers), but there seems to be a lot of misunderstanding of basic physics terms going on here. Plus, I've run across even more in trying to find her powers described further: Yes, Nightcrawler's inertia does not change when he teleports, but I still rather think you meant to say that his momentum does not change when he teleports. Inertia may sound fancier and kinetic energy may sound cooler, but cool and fancy sounding words just make you sound stupid when you use them incorrectly.

I realize that comics are all about suspending disbelief (radioactive spiders, genetic mutation, crime fighting aliens that pass as bumbling reporters) but it's one thing to not limit yourself to what is known or possible, it's another to toss out Newton for no reason. I'm enjoying Runaways, Astonishing X-Men and the new Wonder Woman very much, but I worry that reading most superhero comics would be like watching The Core: I'd laugh hysterically through most of it, and yell during the rest.