Roller Coaster Physics

1. Pick a car from the Car collection. The cars have different masses: 35 g, 50 g and 100 g.
2. Use the Hill 1, Hill 2 and Hill 3 sliders to set how tall each hill is. You can also type a number in the box next to a slider. The car starts at the top of Hill 1.
3. Set the Coefficient of friction. 0 means no friction. A bigger number means more friction.
4. Press Play (the triangle). Watch the Speed and Time above the track. When the car stops, a message tells you what happened to the egg.
5. Use the menu above the graph to pick what to graph: speed (v), kinetic energy (K), potential energy (U), total energy (E), or where the car is (x across, y up). The t axis is time.
6. Press Pause to freeze the car. Press Reset to put the car back at the top. You must reset before you can change the car or the hills.
7. Press Export data to see a table of the run, one row for every 0.05 s. Copy it into a spreadsheet or save it as a file.

Potential energy (U) is stored energy. Here it comes from height. The higher the car is, the more potential energy it has.

Kinetic energy (K) is the energy of motion. The faster the car goes, the more kinetic energy it has.

When the car rolls downhill, potential energy turns into kinetic energy, so the car speeds up. When it climbs a hill, kinetic energy turns back into potential energy, so it slows down.

Total mechanical energy (E) is U + K. With no friction, E stays the same for the whole ride. Energy is not made or lost. It only changes form.

Friction is a force that rubs against the moving car. It changes some of the car's energy into heat (thermal energy). With friction, E goes down as the car rolls, and the car may not make it over the next hill.

A heavier car has more energy at the same height and speed. If the car hits the egg with too much kinetic energy, the egg breaks.

• Potential energy: U = m × g × h
• Kinetic energy: K = ½ × m × v²
• Total mechanical energy: E = U + K
• Use m in kilograms (35 g = 0.035 kg), h in meters (70 cm = 0.70 m), v in meters per second (290 cm/s = 2.90 m/s), and g = 9.81 N/kg. Then the energy comes out in joules (J).
• With no friction, the speed after a drop does not depend on the mass: v = √(2 × g × drop)