Height Energy: mgh

Lesson 2 of 10 · 7 min · Free, no account needed

What you will learn

Lifting something stores height energy (gravitational potential energy): E = m × g × h.
Energy is measured in joules (J). Lifting 1 kg by about 10 cm stores about 1 J.
Twice the mass or twice the height gives twice the energy, so 2 kg up 1 m stores the same as 1 kg up 2 m.

Your phone battery holds about 50 kJ. How high could that much energy lift you?
Drag the marker up the building.
Lift the crate with the crane. Watch the energy column and the graph.
The crate is 2 kg. Take it all the way up.
2 kg up to 1 m, or 1 kg up to 2 m. Which stores more energy?
Tap your pick, then Check: both cranes lift.
Height energy has a formula.
Gravitational potential energy, or height energy: E = m × g × h. m is the mass in kg, g is 9.8 m/s² on Earth, h is the height in metres.
The unit of energy is the joule (J). Lifting a 1 kg bag of sugar by 10 cm stores about 1 J. 1 kJ = 1000 J.
h is measured from a level you choose, like the floor. Simplified model: g is the same at every height we use here.
Store exactly 1000 J in a 5 kg crate.
Turn the dial to set the height, then Check.
Game: Hydro dam. Store each night's energy in the high lake.
Hold Pump to push water up, then press Night. Three nights.
Code: this loop climbs 3 m floors until your phone's energy runs out. Press Run.
It adds a floor, works out m × g × h, and stops once that passes 50000 J.
A 60 kg person climbs 10 floors of 3 m. How much height energy, in kJ?
Your dam kept the city lit. Tap where the energy waited all day.

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