Motion

About this course

Around 1603 Galileo wanted to study falling, but a dropped ball moves too fast to time with the clocks of his day. His answer, published in Two New Sciences in 1638, was to slow gravity down. He rolled a bronze ball down a long, smooth wooden groove at a gentle slope and, in his own account, let water run from a large vessel into a cup during each roll and weighed the water. In equal time intervals the ball covered distances in the ratio 1 : 3 : 5 : 7, so the total distance grew as 1, 4, 9, 16, the squares of the time. That is d = ½ a t², found with a plank and a cup of water.

The seven units start with position, distance and displacement: one lap of a 400 m track is 400 m of distance and zero displacement. Speed and velocity come next, and acceleration after that. Reading motion graphs treats a steeper line as faster. Free fall includes the Apollo 15 moment on 2 August 1971, when Commander David Scott released a 1.32 kg aluminium hammer and a 0.03 kg feather from about 1.6 m and they struck the dust together. Projectile motion follows, where a ball thrown at 20 m/s and 45° stays up 2.9 seconds and lands about 41 m away. The last unit adds air resistance, and a ball that would land 92 m away in a vacuum lands near 60 m in the model. The motion lab launches a ball on Earth, the Moon or Mars and works out time, height and range, with a grey line showing the path without air.