Introduction to Energy


There are various types of energy. For now, we will focus on two types of Mechanical Energy (energy due to movement and position):
Conservative forces are forces for which the energy can be completely recovered.
Gravity and elastic forces are conservative. But friction is not conservative.

Example 1:
If you lift an object, you must apply a force at least equal to the object's weight. F = mg
Lifting the object through a distance d, the work done is PE = W = Fd = mgd
Therefore, PE = weight × height = mgh

Example 2:
The term potential energy implies storing energy to use later for other purposes.
As the archer exerts force on the bow and draw the string back (see figure below)
The (elastic) PE is then released and the force does work on the arrow.
The PE in the bow limbs is transformed into the KE of the arrow.

Example 3:
As illustrate in the figure below, the gravitational force maintains the planets in orbit around the Sun.
Solar System

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Date of last modification: 2024