Topic · 3 games

Gravitation: the pull between masses

Every mass pulls on every other mass with F = G·M·m ÷ r². That one law sets your weight on the Moon, keeps satellites in orbit, and fixes how long every planet takes to go around the Sun.

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3 games

PLAY NOW · 29

Planet Scale: Gravity on Other Worlds

Weigh an astronaut and drop a ball on the Moon, Mars, and a super-Earth. Predict g = G·M ÷ R², the weight W = m·g, and the fall time, and find out what happens to the mass.

Surface gravityWeight and mass
Play Planet Scale
Surface gravity
g = G·M ÷ R²
Weight
W = m·g

PLAY NOW · 30

Satellite Launch: Universal Gravitation

Launch a satellite above Earth. Use F = G·M·m ÷ r² to predict the pull, see why twice as far means a quarter of the pull, and find the speed for a circular orbit and the geostationary radius.

Universal gravitationOrbits
Play Satellite Launch
Universal gravitation
F = G·M·m ÷ r²
Circular orbit
v = √(G·M ÷ r)

PLAY NOW · 31

Kepler's Clock: Periods and Distances

Time the Moon, Jupiter's moons, Earth, and Mars. Use Kepler's third law, T² = 4π²·r³ ÷ (G·M), to predict periods, weigh Jupiter, and find how far Mars is from the Sun.

Kepler's third lawOrbital period
Play Kepler's Clock
Kepler's third law
T² = 4π²·r³ ÷ (G·M)
Mass from an orbit
M = 4π²·r³ ÷ (G·T²)

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