Matter
Atoms (“indivisible”)
• 3 parts: protons, neutrons, electrons
nucleus
(p+) (no) (e-)
Atomic Number = # of protons in nucleus (defines element)
Each element can be found in different varieties (Isotopes)
Chemical Bonds
Two (or more) atoms can form new substances by bonding to each
other by sharing electrons (covalent) or exchanging electrons (ionic).
H
O
C
Molecule – two or more atoms chemically bonded
N
H2
O2
Compound – molecules made of two or more elements
H2O
NH3 (ammonia)
Organic Molecule – molecules that contain carbon (life)
C4 H 8
Temperature
Measurement of the average energy of atoms within a substance
Low energy = Cold
High energy = Hot
Ways to increase energy:
- Add heat (e.g. light)
- Increase the pressure of the substance by adding more
force or shrinking the volume
States of Matter:
Matter will change states based on temperature (pressure)
The Nature of Light
Light can be described as a long continuous wave (classical) OR
as a packet of energy called a “photon” (quantum)
Continuous Wave
Photon
Wave Properties
Velocity (v) – speed at which the wave moves
Wavelength (λ) – distance over which a wave repeats
Electromagnetic Spectrum
A photon with a small wavelength has high energy
Reflection – the “bouncing” of light off of surfaces
Law of Reflection: Reflected angle = Incident angle
Refraction – the “bending” of light as it passes from one
medium to another
Revolutionized physics with publication of Principia Mathematica
• Principles of optics
• Development of calculus
• Laws of motion
• Law of gravity
• Derives Kepler’s Laws of Planetary Motion
Isaac Newton (Britain)
Laws of Motion
1st law of motion: object @ rest (in constant motion) will stay that way
unless an outside force acts on it (Law of Inertia)
2nd law of motion: Force on an object = mass x acceleration
F = ma
3rd law of motion: every force is countered by another that is equal in
magnitude and opposite in direction.
FA = - FB
Newton’s Law of Gravity
Force of gravity between two objects depends:
• Directly on the mass of each object
• Inversely on the square of the separation
GMm
F=
2
r
G ≡ Gravitational Constant
= 6.67 x 10-11
r = 1.5 x 1011 m
MSun = 2 x 1030 kg
MEarth = 6 x 1024 kg
(6.67 x 10 -11 ) (2 x 1030 ) (6 x 10 24 )
F =
(1.5 x 1011 ) 2
= 3.56 x 1022 N
Planetary Properties
Surface Gravity – strength of a planet’s gravitational pull at its surface
- depends on a planet’s size & mass
Earth’s surface gravity
9.8 m/s2 (1 g)
Moon’s surface gravity
1.6 m/s2 (1/6 g)
Weight = mass x surface gravity
W = mg
Planetary Properties
Escape Velocity – speed required to escape a planet’s gravitational pull
Earth’s escape velocity:
11 km/s
25,000 m.p.h.
Laws of Planetary Motion
Planet
Sun
Perihelion
Aphelion
Johannes Kepler (Germany)
1st: Planetary orbits are elliptical w/ the Sun @ one focus
Planetary Properties
Semi-major axis (a) – average distance between Sun and planet
c
a
Eccentricity (e = c/a) – describes the “flatness” of the ellipse
Kepler’s Laws of Planetary Motion
2nd : A line connecting a planet to the Sun will “sweep out”
equal areas in equal time
1 month
1 month
1 month
Kepler’s Laws of Planetary Motion
3rd: The orbital period (Porb) is related to the average distance (a)
according to the relation:
2
(Porb ) = (a)
Planet
3
a (AU)
a3
Porb (yrs)
(Porb)2
Mercury
0.387
0.05796
0.241
0.05808
Venus
0.723
0.37793
0.615
0.37823
Mars
1.524
3.5396
1.881
3.5382
Jupiter
5.204
140.93
11.86
140.66
Saturn
9.582
879.77
29.46
867.89
Planetary Properties
Orbital Plane: “flat surface” that a planet’s orbit lies on
Earth’s orbital plane = “ecliptic plane”
Side View
Top View
Orbital Inclination (iorb) – angle a planet’s orbital plane makes with
respect to the ecliptic plane
Planetary Properties
Rotational Inclination (irot) – angle a planet’s rotational pole makes
with respect to the normal to the orbital plane
Earth: irot = 23.5º
Planetary Properties
Average density (ρ) – ratio of a planet’s mass to its Volume (m/Vol)
Material
Iron
Rock
Water
Oak
Air
Density (g/cm3)
7.86
2.0 – 5.5
1.0
0.6 – 0.9
0.0013
Albedo – the fraction (%) of sunlight reflected by a planet (0 – 1.0)
High albedo indicates: presence of an atmosphere
liquid/ice on surface of a planet
Planetary Properties
Surface Gravity – strength of a planet’s gravitational pull at its surface
- depends on a planet’s size & mass
Earth’s surface gravity
9.8 m/s2 (1 g)
Moon’s surface gravity
1.6 m/s2 (1/6 g)
Weight = mass x surface gravity
W = mg
Planetary Comparison
Solar System planets are separated into two groups:
• Terrestrial (Earth-like) – Mercury, Venus, Earth, Mars
• Jovian (Jupiter-like) – Jupiter, Saturn, Uranus, Neptune
Property
Terrestrial
Jovian
Pluto
a (AU)
0.39 – 1.52
5.2 – 30.1
39.48
Porb (yrs)
0.24 – 1.88
11.9 – 163.7
248
e
0.007 – 0.21
0.009 – 0.054
0.25
iorb
0° - 7°
0.8° - 2.5°
17.1°
Req (Earth radii)
0.38 - 1
3.87 – 11.0
0.18
M (Earth masses)
0.055 – 1
14.5 - 318
0.0025
ρavg (g/cm3)
3.93 – 5.52
0.69 – 1.64
1.1
Prot (days)
1 – 243
0.41 – 0.73
6.39
Oblateness
0 – 0.005
0.03 – 0.11
~0
Albedo
0.11 – 0.65
0.41 – 0.52
0.3