Mechanical Energy is the sum of Potential Energy and Kinetic Energy

It is the energy that is possessed by an object due to its motion or due to its position. Mechanical Energy is constant in only gravitational forces or in an otherwise idealized system – such that non-conservative forces like friction and air resistance can be reasonably neglected.

What is Potential Energy?Edit

Potential Energy is energy due to position. Systems or objects with potential energy are able to exert forces (exchange energy) as they change to other arrangements.

Gravitational potential energy describes the energy of an elevated object. The term is often shortened to just "potential energy" in physics because the most common type of potential energy in physics problems is gravitational. Unless otherwise stated, you can assume "potential energy" means gravitational potential energy.

Potential Energy Equation

Potential Energy Equation

The equation used to calculate an object's the potential energy is listed at right:

What is Kinteic Energy?Edit

Kinetic energy is energy of motion.

Objects that are moving also have the ability to cause change. Kinetic energy can easily be transfered into potential energy - The kinetic energy of a basketball tossed upward converts into potential energy as the height increases. Also, the amount of kinetic energy an object has equals the amount of work the object can be exerting force as it stops. Kinetic energy is related to the object's mass and speed.

The equation used to calculate an object's kinetic energy is listed at right:
Kinetic Energy Equation

Kinetic Energy Equation

Real World SituationEdit

The study of mechanical energy is useful because:

1. You will know how much potential energy a textbook in your hand have, by knowing the weight of the book and the height of your hand to the ground.

2. You will know how much kinetic energy a car has while travelling in a constant velocity, by knowing the mass of the car and the velocity it has.

3. By the time you throw a ball in the air, you know that the energy transforms from kinetic energy to potential energy then back to kinetic energy.

Word ProblemsEdit


A weightlifter lifts up a barbell with a mass of 214 kg for 2 meters. How much potential energy does the barbell have?

Use Equation: Ep = mgh

Known: m = 214 kg

             g = 9.8 m/s²

             h = 2 m


            Ep = 214 × 9.8 × 2 = 4194.4 (J)

The barbell has a potential energy of 4194.4 joules.


For a bullet weigh 0.1372 N with a speed of 300 m/s, how much kinetic energy does it have?

Use Equation: Ek = 1/2mv²

Known: m = 0.1372 N/ 9.8m/s² = 0.014 kg

             v = 300 m/s


           Ek = 1/2 × 0.014 × 300² = 630 (J)

The bullet’s kinetic energy is 630 joules.

Topic ReflectionEdit

All studies of physics are useful in real lives. By studying Mechanical energy, we simply know more about how energy can cause change in itself or in other objects. The idea that “Energy can never be created nor destroyed” tells us more of how the world works and organizes. The conservation and study of potential energy and kinetic energy helps us to solve more real life situations, which will make life easier for all of us.

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