What is the physics behind shake flashlights? What is the physics behind shake flashlights? From what I have read and from what I have seen when I tore one apart is that it is simply a magnet, coiled wire, a capacitor, and a light bulb. Mechanically it appears that by shaking the unit you are forcing a magnet to go through the center of the coiled wire. 
What I do not understand is how this would power a light bulb. What is the physics behind this phenomenon. Both specifically in this situation, and even generally, how would a magnet generate power?
 A: The physics you are looking for is electromagnetic induction (https://en.wikipedia.org/wiki/Electromagnetic_induction#Electrical_generator)
When you move a permanent magnet relative to a conductor (the copper wire), the magnetic field of the magnet influences the electrons in the copper, creating a current. Really, the energy that you put in to the system by shaking the flashlight is converted to electricity. This is how electrical generators work.
A: Koldrakan’s answer explains how the energy is generated. But you might be confused as to why the bulb keeps glowing for some time rather than the light itself fluctuating with the shake. 
If you didn’t already know this, that's due to the capacitor. A capacitor can store energy in the form of charge. When you shake it the electric energy generated gets stored in the capacitor. The circuit is designed in a way that rectifies the AC generated into DC. This DC charges the capacitor and then when you stop shaking it, the capacitor discharges automatically. The DC from the discharging capacitor powers the light bulb.
A: An important point not yet mentioned is that if electrical energy were not taken from the coil, each shake would add kinetic energy to the magnet as it was accelerated to match the velocity of the flashlight; after the flashlight stops, the sliding magnet would then continue until it reached its end of travel, whereupon the magnet would apply some of the kinetic energy back to the flashlight and possibly keep some itself as it rebounds in the opposite direction.  Current in the coil, however, will induce a magnetic force in the direction opposite the magnet's relative motion, thus reducing the amount of kinetic energy the magnet will have when it hits the end of travel.
