When a light switch is turned on, electrical energy runs through the wires and is transferred to the bulb where electrical energy is converted to light and heat energy. This is an example of energy transfer. When a bowling ball that has kinetic energy strikes the bowling pins which are stationary, energy is transferred from the ball to the pins, causing the pins to move.
Energy can be neither created nor destroyed, according to the law of conservation of energy, but it can change from one form to another or transfer from one object to another. A rock placed on a tall cliff has potential energy due to the height at which it is placed. If the rock starts to fall, its potential energy is changed to kinetic energy since the rock traded in the height of its position for velocity of its movement.
Electrical energy is changed to kinetic energy when a fan is turned on. Chemical energy of food is changed to mechanical energy whenever organisms do work. Batteries convert chemical energy to electrical energy to power various devices. Electric generators convert the chemical energy of gasoline to kinetic energy to move a coil of wire relative to a magnet to generate electrical energy. When a stationary book on a table is pushed, energy from the person pushing it is transferred to the book, causing the book to move. When striking a drum, the kinetic energy of the stick changes to sound energy.