Question

if a bar magnet is throw into a coil of wire, it will slow down. WHY??

Answer 1

Because a moving magnetic field will generate an electric current in a coil of high resistance wire. And the electric current in the coiled wire will in turn generate a magnetic field equal in polarity with the original magnetic field. Since same polarity magnetic fields opposes each other, this would then cause the bar magnetic to slow down and eventually stop.