Two Body Orbits (M + m)P2 = a3 It does! Center of Mass How come the Sun doesn’t go around the Earth? It does! Center of Mass The Center of Mass is where the two masses would balance The objects go around each other (M + m)P2 = a3

Applies to planets around the Sun Kepler Vs. Newton Applies to planets around the Sun P2 = a3 (M + m)P2 = a3 Always applies Masses in Solar Masses Sun + Earth M + m = 1 + .000003  1

Gravity Vs. Pressure = Sphere Gravity wants to squish everything to a point Pressure wants it to spread out They balance to make a sphere If an object rotates, it makes a flattened (oblate) sphere Small objects can be any shape

Precession Gravity pulls unevenly on the flattened Earth Earth is like a top – its tilt changes over time 26,000 year cycle

Gravity vs. Rotation = Disk Dust or gas or chunks - disk forms Rotation keeps it from falling in Gravity keeps it from escaping Rings around Planets Spiral Galaxies Accretion disks Protoplanetary disks

Tidal Forces

Q. 11: How Often Do Tides Occur? Tidal Distortion Greatly Exaggerated Q. 11: How Often Do Tides Occur?

Spring (Big) and Neap (Small) Tides Big Tides Small Tides

Bulges and the Earth/Moon System with rotation without rotation Earth Earth Moon Q. 12: Tidal Locking Earth and Moon bulge want to align Strong effect on the Moon Rotation causes bulge to be in wrong place Bulge has gravitational pull on Moon Earth rotation slows Moon slung to higher, slower orbit

Tidal Locking Moon Earth Moon Moon Moon

Tidal Heating planet moon Changing shape as distance changes Flexing generates heat planet moon

Roche Limit Planet Moon

Q. 13: Titan and Tidal Forces Roche Limit - Rings Q. 13: Titan and Tidal Forces

Light and Other Electromagnetic Waves Energy Energy is ability to do work Energy comes in many forms Energy can change forms Nuclear Heat Light Chemical Kinetic (motion) Gravitational Heat

Some Types of Energy Kinetic Energy – Energy of motion Heat is actually kinetic energy Electric and Magnetic Energy Light is a kind of electromagnetic energy Gravitational When two objects are far apart, they have a lot of gravitational energy Nuclear energy Powers the Sun and stars