MCAT Physics and Math 2: Concept Summary

Energy is the property of a system that enables it to do something or make something happen, including the capacity to do work. The SI units for all forms of energy are joules (J).

Kinetic energy is energy associated with the movement of objects. It depends on mass and speed squared (not velocity).

Potential energy is energy stored within a system. It exists in gravitational, elastic, electrical, and chemical forms.

Gravitational potential energy is related to the mass of an object and its height above a zero-point, called a datum.

Elastic potential energy is related to the spring constant (a measure of the stiffness of a spring) and the degree of stretch or compression of a spring squared.

Electrical potential energy exists between charged particles.

Chemical potential energy is the energy stored in the bonds of compounds.

The total mechanical energy of a system is the sum of its kinetic and potential energies.

Conservative forces are path independent and do not dissipate the mechanical energy of a system.

If only conservative forces are acting on an object, the total mechanical energy is conserved.

Examples of conservative forces include gravity and electrostatic forces. Elastic forces, such as those created by springs, are nearly conservative.

Nonconservative forces are path dependent and cause dissipation of mechanical energy from a system.

While total energy is conserved, some mechanical energy is lost as thermal or chemical energy.

Examples of nonconservative forces include friction, air resistance, and viscous drag.

Work is a process by which energy is transferred from one system to another.

Work may be expressed as the dot product of force and displacement, or the product of force and distance traveled with the cosine of the angle between the two.

Work may also be expressed as the area under a pressure–volume (P–V) curve.

Power is the rate at which work is done or energy is transferred. The SI unit for power is the watt (W).

The work–energy theorem states that when net work is done on or by a system, the system’s kinetic energy will change by the same amount. In more general applications, the work done on or by a system can be transferred to other forms of energy as well.

Mechanical advantage is the factor by which a simple machine multiplies the input force to accomplish work.

The six simple machines are the inclined plane, wedge, wheel and axle, lever, pulley, and screw. Simple machines provide the benefit of mechanical advantage.

... the input force necessary to accomplish the work is reduced; the distance through which the reduced input force must be applied, however, is increased by the same factor (assuming 100% efficiency).

Efficiency is the ratio of the machine’s work output to work input when nonconservative forces are taken into account.