Pre-lecture: Gravitation
- Earlier we talked about mg
- It turns out that is an approximate form for the interaction between two objects with mass, which i'll describe now
- Consider the Earth and the Moon.
- Certainly, you've heard the Earth and Moon are attracted to each other
- That attraction is how the Earth and Moon interact – through the gravitational force – it is a force that involves no contact
- Newton developed the model for universal gravitation by studying data collected by Brahe and Kepler
- Used it to predict the motion of astronomical objects
- Here's Earth and Moon
- The force that the Moon exerts on the Earth
- Write out equation
- Describe all the bits (G, separation vector, minus sign, unit vector)
- What about Earth on Moon? different separation vector
- This force is really weak; astronomical objects are affected by gravity
- On Earth, most objects are unaffected by the gravitational interaction with other objects, because overwhelming affected by interaction with Earth.
- But we already have a model for that - mg = GMEm/RE^2
- Motion? Objects move in elliptical orbits (special case circular)
- Predicting the motion of astronomical objects in general requires computation