since velocity is always based on a frame of reference, can I just change my frame of reference to have different amounts of kinetic energy? Where does that energy come from?
In: Physics
Yes and no.
While not usually elaborated as such, the kinetic energy of an object is usually assumed to be in reference to something. For example, when car is driving on a highway, the kinetic energy of the car implies in relation to a stationary object on earth. But if you consider your reference point to be the Sun, then the kinetic energy of the car is much higher, because the velocity is now not the 100 kph, but more like 1600 kph.
Or imagine two people in different cars driving parallel to each other throwing apples at each other. The kinetic energy of those apples is relatively small when hitting each other, but if you miss and hit an innocent pedestrian, he will be hit with an apple with kinetic energy much higher, due to combined velocity of the apple throw + velocity of the car from where the apple was thrown. Basically the resultant kinetic energy comes from the difference in relative velocities of two objects
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