3 It is important to realize that in physics today, we have no knowledge of what energy is. Richard P. Feynman
4 When is expenditure of energy required? * tossing a ball* lifting a rock* launching a rocketWhen is expenditure of energy not required?* Rocket coasting through space
5 Satellite orbitingEarth requires noexpenditure ofenergy.Expenditure of energy seems torequire motion and force.
6 Some Varieties of Energy * Kinetic Energy (Energy of Motion)> Thermal (heat) energy* Potential Energy (Stored Energy)> Elastic energy> Gravitational energy> Chemical energy> Electrical energy> Magnetic energy> Mass-energy* Radiative Energy
7 Kinetic Energy (KE)Mass (m)Speed (v)* KE m* KE v2
20 Atoms are usually neutral: # protons = # electrons Ions: atoms with one or more electrons added and/or removed A chemical element consists of atoms with equal numbers of protons
21 Isotopes consist of atoms of an element with a different number of neutrons #protons #neutronse.g.,Hydrogen 1 0DeuteriumTritium Atoms can bind together in molecules A molecule is the smallest unit of a compounde.g., CO2, H2O, etc