ASTR 101 1st Edition Lecture 10 Outline of Last Lecture II Clicker questions III Conservation laws in astronomy IV Basic types of energy Outline of Current Lecture I The force of gravity II Changing orbit III Tides and phases of the moon Current Lecture I The force of gravity a What determined the force of gravity First you must have 2 objects They objects are separated by the distance r Define the mass of the 2 objects The larger the mass the stronger the force b How does newton s law of gravity extend Kepler s law Kepler s first 2 laws apply to all orbiting objects not just planets Ellipses can be more than just orbital paths II Changing an orbit a It s not that easy to change an orbit because the angular momentum and energy are both conserved unless an external force is applied EX if a comet comes into our solar system it may temporarily orbit the sun and then fly off With Jupiter though it may transfer some angular momentum and then settle into a new orbit around the sun b Escape velocity if you throw something hard enough it will escape It doesn t matter how heavy the object is it just needs speed EX you could shoot a bullet through with strong enough velocity and it will escape Escape velocity from the Earth 11 km sec which is very fast III Tides and phases of the moon a The moon s speed in rotation is locked we see only one side of the moon tidal interaction The tidal bulge of the Earth is misaligned with the moon This changes the gravitational force between the Earth and the moon if the Earth rotates faster the moon will produce a drag to bring it back The tidal force also has a reverse effect on the moon The bulge pulls the moon ahead increasing its These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute orbital distance The moon is being accelerated by the Earth when it passes some of its angular momentum to the moon which means that the moon s distance from the Earth is actually increasing with time