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## Chapter summary

• The gravitational potential energy of an object is the energy the object has because of its position in the gravitational field relative to some reference point.

• The kinetic energy of an object is the energy the object has due to its motion.

• The mechanical energy of an object is the sum of the potential energy and kinetic energy of the object.

• The unit for energy is the joule (J).

• The Law of Conservation of Energy states that energy cannot be created or destroyed, but can only be changed from one form into another.

• The Law of Conservation of Mechanical Energy states that the total mechanical energy of an isolated system (i.e. no friction or air resistance) remains constant.

• The table below summarises the most important equations:

Table 1
 Potential Energy $E P =mgh$ Kinetic Energy $E K =1 2mv 2$ Mechanical Energy $E M =E K +E P$
Table 2: Units used in mechanical energy
 Physical Quantities Quantity Unit name Unit symbol Potential energy ($E P$) joule J Kinetic energy ($E K$) joule J Mechanical energy ($E M$) joule J