Physics by topic

Each topic is a ladder of 8 levels, and each level holds several full lessons. It starts with something you can try with your hands and climbs, one level at a time, to the physics of the end of high school and a first step beyond. Every topic keeps coming back to one question: what would this mean on Mars?

Every lesson has the same parts: a question to start, the idea explained with pictures, worked examples, questions to try (answers hidden until you tap them), a common mistake, and where it leads.

For parents and teachers: level 1 suits most children from about 5, level 3 from about 9, level 5 from about 12, level 7 from about 15, and level 8 is the bridge to university. These are rough guides; curious readers ignore them.

Topics

Topic	From	To
Gravity and orbits	Why things fall down	Hohmann transfers, launch windows and Lagrange points
Rockets and landing	A balloon that flies	The rocket equation and landing in thin air
Forces and motion	Pushes and pulls	Newton's laws, friction and circular motion
Energy and power	What makes things go	Solar power at Mars's distance, batteries and reactors
Heat and matter	Hot and cold	Gases, pressure and boiling at 70 kPa
Air and fluids	Wind and bubbles	Lift, drag and a helicopter in air sixty times thinner
Waves, sound and light	Echoes and rainbows	Spectra, telescopes and the blue sunsets of Mars
Electricity and magnetism	Magnets and batteries	Fields, motors and a planet that lost its magnetic field
Radiation and the atom	What everything is made of	Cosmic rays, doses and shielding a city
Space and time	How fast is light?	Radio delay, clocks on Mars and relativity