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# Test yourself now

High marks in science are the key to your success and future plans. Test yourself and learn more on Siyavula Practice.

## Chapter summary

Presentation: VPfvd

• 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 ($$\text{J}$$).

• 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:

 Potential Energy $${E}_{P}=mgh$$ Kinetic Energy $${E}_{K}=\frac{1}{2}m{v}^{2}$$ Mechanical Energy $${E}_{M}={E}_{K}+{E}_{P}$$
 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

Table 22.1: Units used in mechanical energy