How it works
Gravitational potential energy is stored height: mass × gravity × elevation. Lift something up and you bank energy; let it fall and the bank pays out as motion, heat or electricity.
The numbers are humbling. Carrying 75 kg up 10 m of stairs stores only 7,355 J — under 2 food-calories. Human effort is worth astonishingly little in energy terms, which is exactly why cheap electricity transformed civilisation.
Entire industries run on this equation: hydroelectric dams convert the mgh of elevated water into a fifth of the world's electricity, and pumped-storage plants are the planet's biggest 'batteries' — they store energy by pumping water uphill.
Use it in real life
Home energy intuition: one kWh — a few cents of electricity — equals hauling 3,670 kg up 100 m. Understanding this gap explains why electric machines beat manual labour everywhere.
Hydropower: a reservoir 100 m above its turbines yields ~0.27 kWh per tonne of water. Scale explains everything about why dams are enormous.
Exercise: climbing stairs burns calories at a physics-calculable floor rate (plus your body's ~75–80% inefficiency, which turns 2 kcal of pure lifting into ~8–10 kcal actually burned).
Frequently asked questions
Does potential energy depend on the path taken?
No — only on net height gained. Taking the long gentle ramp or the steep stairs stores exactly the same energy (the stairs just demand more power, i.e. energy per second).
How much energy does a hydroelectric dam get per litre?
PE = mgh: one litre (1 kg) falling 100 m yields 981 J, about 0.27 Wh. A large dam moves millions of litres per second — that's the trick.
Why do I burn more calories than mgh predicts when climbing?
Muscles are ~20–25% efficient, you also move limbs, balance, and generate heat. mgh is the physics floor; your metabolism pays 4–5× that.