This interactive is used in Chapter 5.
This Interactive is as much a game as it is an educational experience: you could call it the Isaac Newton Universal Gravitation Challenge. Place yourself on the Sun, the Moon, or any of the planets, and fire a cannonball with such precision that its trajectory lands it on a target. You’re trying to balance the force of gravity, which depends on the size and mass of the world on which you stand (or hover, for worlds with no solid surface). Now, choose your world, feel the force, and fire!