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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