PHYSICS 50: Lecture 11.1 RICHARD CRAIG

Homework #11 Chapter 12 We will skip , 12.13, 12.23, 12.54, Due Tuesday April 22

Today Force of Gravity Examples Acceleration due to gravity Gravitational Potential energy Escape velocity Circular Orbits Examples

Newton’s Law of Gravitation There is a force of attraction between any two masses F = Gm 1 m 2 /R 2 G is a universal constant G = 6.67 x Nm 2 /kg 2

Newton’s Law of Gravitation

Examples Me and you Me and earth Three particles

Calculate gravitational variables To add forces due to multiple masses you must add vectors

Weight (skip Weight Watchers, just climb upward) Gravity (and hence, weight) decreases as altitude rises.

Things that effect your “weight” Altitude Latitude “Local” variations in rocks Barometric pressure

Gravitational force changes densities below sea level Just as it’s interesting to remember that all gravitational forces are calculated from the center of the planet, it’s interesting to follow the density as one proceeds from crust to mantle to core. “Want to get away”? Consider Example 12.4 to calculate gravity on Mars.

Gravitational potential energy Objects changing their distance from earth are also changing their potential energy with respect to earth.

If an object has enough kinetic energy to overcome the gravitational potential energy it can escape from the gravitational pull 1/2 mv 2 > GmM/R Escape Velocity

Satellite motion

Consider satellite orbits

Circular Orbit Examples Low Earth Orbit (LEO) Geosynchronous orbit Moon