Matter & Energy

Give me matter and motion, and I will construct theuniverse.

Rene Descartes

ENERGY

It is important to realize that in physics today,we have no knowledge of what energy is.

Richard P. Feynman

When is expenditure of energy required?

* tossing a ball* lifting a rock* launching a rocket

When is expenditure of energy not required?

* Rocket coasting through space

Satellite orbitingEarth requires noexpenditure ofenergy.

Expenditure of energy seems torequire motion and force.

* 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

Some Varieties of Energy

Kinetic Energy (KE)

Mass (m)

Speed (v)

* KE m

* KE v2

2mv2

1 KE

Heat & Temperature

Higher Temp. Lower Temp.

Conservation of Energy

Energy neither appears nor disappears. It may be converted from one kind to another, in whichcase the total amount of energy is unchanged.

Conservation of Energy + Mass

* Einstein: mass and energy are interchangeable

2mc E mass

(speed of light)2

* Total of mass + energy is what’s really conserved!

0.1 kg mass Energy

equivalent to detonating

1 million tons TNT(1 ‘megaton’)

MATTER

ATOMS

When it comes to atoms, language can be usedonly as in poetry. The poet, too, is not nearly so concerned with describing facts as withcreating images.

- J. Bronowski

Old Picture:

ElectronsorbitNucleus:

larger orbit moreenergy

(‘Bohr Atom’)

New Picture

Electron ‘cloud’

Distance from Nucleus

Pro

bab

ilit

y of

Fin

din

g E

lect

ron

lowest energy

next lowest energyor

or ornext lowestenergy

In 3-D

HydrogenEnergyLevels(1 electron)

Ground State

Excited States

SodiumEnergyLevels(11 electrons)

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

Isotopes consist of atoms of an element with a different number of neutrons

#protons#neutrons

e.g.,Hydrogen 1 0 Deuterium 1 1 Tritium 1 2

Atoms can bind together in molecules

A molecule is the smallest unit of a compound

e.g., CO2, H2O, etc

Phases of Bulk Matter

• Solid

• Liquid

• Gas

• Plasma

Tem

per

atu

re

(Avg

. Kin

etic

En

ergy

)

Solid

Liquid

Gas

Plasma

Fully Ionized