We start with a ball. Why does it fall, why does a helium balloon do the opposite, and how quickly does gravity work on each of them? Then we throw the ball upwards and watch it come back, and then we throw it sideways instead; and we keep throwing it harder until it stops coming back at all. That is all an orbit is.
This explains why astronauts float, which has nothing to do with being beyond the reach of gravity, and it sets up the real problem. Staying in orbit takes enormous speed; speed takes propellant; and propellant has mass of its own that must also be carried. We look at why a rocket is mostly fuel, why the Saturn V was built in stages, and at the only three ways out of the difficulty: carry more, use what you carry more efficiently, or start somewhere other than the ground.
There are no equations on screen; it is thirty minutes, a lot of photographs, and a single idea followed all the way through.
What people leave with
- Why an orbit is really just falling sideways fast enough to keep missing the ground
- Why astronauts float, which is not because gravity has stopped
- Why rockets are mostly propellant, and why that forces them to be staged
What the room needs
- Nothing but a power socket; I bring my own laptop, projector, screen, speakers and extension lead
Where it sits
This talk is ringed. The others are links.