Download This lesson introduces mechanical energy, the form of energy that is

This lesson introduces mechanical energy, the form of energy that is easiest to observe on a daily
basis. All moving objects have mechanical energy. There are two types of mechanical energy:
potential energy and kinetic energy. Potential energy is the energy that an object has because of
its position and is measured in Joules (J). Potential energy can also be thought of as stored
energy. Kinetic energy is the energy an object has because of its motion and is also measured in
Joules (J). Due to the principle of conservation of energy, energy can change its form (potential,
kinetic, heat/thermal, electrical, light, sound, etc.) but it is never created or destroyed.
Within the context of mechanical energy, potential energy is a result of an object's position, mass
and the acceleration of gravity. A book resting on the edge of a table has potential energy; if you
were to nudge it off the edge, the book would fall. It is sometimes called gravitational potential
energy (PE). It can be expressed mathematically as follows:
PE = mass x g x height or PE = weight x height
where PE is the potential energy, and g is the acceleration due to gravity. At sea level, g = 9.81
meters/sec2 or 32.2 feet/sec2. In the metric system, we would commonly use mass in kilograms
or grams with the first equation. With English units it is common to use weight in pounds with
the second equation.
Kinetic energy (KE) is energy of motion. Any object that is moving has kinetic energy. An
example is a baseball that has been thrown. The kinetic energy depends on both mass and
velocity and can be expressed mathematically as follows:
Here KE stands for kinetic energy. Note that a change in the velocity will have a much greater
effect on the amount of kinetic energy because that term is squared. The total amount of
mechanical energy in a system is the sum of both potential and kinetic energy, also measured in
Joules (J).
Total Mechanical Energy = Potential Energy + Kinetic Energy
Engineers must understand both potential and kinetic energy. A simple example would be the
design of a roller coaster — a project that involves both mechanical and civil engineers. At the
beginning of the roller coaster, the cars must have enough potential energy to power them for the
rest of the ride. This can be done by raising the cars to a great height. Then, the increased
potential energy of the cars is converted into enough kinetic energy to keep them in motion for
the length of the track. This is why roller coasters usually start with a big hill. As the cars start
down the first hill, potential energy is changed into kinetic energy and the cars pick up speed.
Engineers design the roller coaster to have enough energy to complete the course and to
overcome the energy-draining effect of friction.
Your Task:
1. Calculate Potential Energy
a. PE = mass x g x height or PE = weight x height
2. Calculate Kinetic Energy
a.
3. Calculate Total Mechanical Energy
a. Total Mechanical Energy = Potential Energy + Kinetic
Energy