Energy is the ability to cause change or do work. There are many forms of energy: mechanical, kinetic, potential, electrical, solar, sound, chemical, etc.
Mechanical energy is the total energy of a system. It is the sum of potential energy (energy of position) and kinetic energy (energy of motion).
Examine the image to the right. The coaster is at the top of the hill, and assuming that it is not moving, it has potential energy. When the coaster begins moving, the potential energy converts to kinetic energy.
Kinetic energy (KE) has the formula: ½ mv2 (v is squared) where m is mass and v is velocity (m/s)
There are two variations of potential energy (PE). Gravitational potential energy (GPE) is the stored energy of an object as a result of its mass and height. The formula is
GPE = m * g * h where m is mass (kg), h is height (m), and g is gravity (9.8 N/kg)
Elastic potential energy (EPE) is the energy stored in elastic materials as the result of their stretching or compressing ability. It is the energy found in rubber bands, bows, springs, trampolines, etc.
Mechanical energy (ME) = KE + PE allows an object to do work. Whenever PE > 0, KE = 0. Whenever KE > 0, PE = 0. KE and PE can’t have values at the same time, as one represents position and the other represents motion.
Work (W) is when a force acts on an object to cause displacement. In other words, work is force applied through a distance. Work is done only when force is directly applied. Once the force is no longer applied, work is no longer being done.
W = f * d where force is in newtons (N) and distance is in meters (m). The unit for work is joules (J). However, a more accurate formula for work includes multiplying by the cosine of angle theta. There are three main scenarios:
Any scenario involves some angle between the force and the displacement vector.
Simple machines do work with one movement of the machine. There are six simple machines: lever, pulley, wedge, screw, inclined plane, and wheel/axle.