Energy on a Track: Kinetic and Potential Energy
Release a cart from rest on a curved track and watch its energy change hands. Going down, stored (potential) energy becomes motion (kinetic) energy, and climbing again stores it back. Live bars show the kinetic, potential and heat energy in joules, and the total never changes. Add friction to see energy turn into heat, so each swing is lower than the last until the cart stops. Change the track, height, mass and gravity, and start high enough on the hilly track to roll right over the hill and off the end.
Preview — sign up free to change the numbers yourself
What you can adjust
- Track shape
- 0 – 2
- Release height
- 1 – 10 m
- Mass of the cart
- 0.5 – 5 kg
- Friction coefficient
- 0 – 0.3
- Gravity
- 1.6 – 24.8 m/s²
Valley is a smooth bowl. Valley and hill has a 7 m hill on the right, and a cart with enough energy rolls over it and off the end. Double dip has a 4 m hill between two dips.
How high above the lowest point of the track the cart starts, at rest on the left slope. The higher it starts, the more energy it has.
A heavier cart has more energy to start with, but it moves in exactly the same way: the mass cancels out of the motion.
How rough the track is. At 0 the track is perfectly smooth and the cart never loses energy. A higher value turns more energy into heat on every metre it travels.
The strength of gravity on the cart. A stronger pull gives it more energy at the same height, and makes it move faster.
About this simulation
What it shows
A cart is let go from rest on a curved track. Live bars show its kinetic (motion), potential (height) and thermal (heat) energy in joules next to their total, with its speed, height and time beside them.
The key idea
Energy is not used up, it is moved between stores. Going down, potential energy becomes kinetic energy; going up, it changes back. Friction moves some energy to the thermal store for good, so the total stays the same but each swing is lower.
Try this
Set Friction coefficient to 0 and the cart swings back to its starting height every time. Then set Release height to 10 m on Valley and hill: it rolls off the end at about 12.9 m/s.
A simple model: the cart is a point that stays on the track, the friction is the same everywhere and there is no air resistance. The cart stops where friction can hold it. The mass changes how many joules there are but not the motion.