Unit 18
Orbits and spaceflight.
Real spaceflight: Kepler's laws, escape speed, the Lagrange points, and what a rocket gets from its fuel.
Before this unit
The unit, lesson by lesson
Lessons
4 lessons · 26 practice questions · about 2 hours
Kepler's laws
Orbits are ellipses with the Sun at one focus, a planet is faster when it is close to the Sun, and the length of the year depends only on the size of the orbit.
Escape velocity
How fast you have to go never to come back. Kinetic energy against the well of gravity, the escape speed from the Earth, the Sun and the Moon, and stretched orbits that come close to it.
Lagrange points
Five points where a probe goes round the Sun in step with the Earth. Why L1 and L2 are so close to the Earth, why they are unstable, and why L4 and L5 hold asteroids.
Rockets and the rocket equation
A rocket throws mass backward and gets momentum forward. Tsiolkovsky's rocket equation, why each last per cent of propellant is worth more, the exhaust speed, stages, and what it takes to reach orbit.