Torricelli's Tank (Draining Through a Hole)
Punch a hole in the side of a water tank and watch the jet arc out and the level fall — the jet speed depends only on how deep the hole is below the surface, and the tank empties on a curve you can predict.
Preview — sign up free to change the numbers yourself
What you can adjust
- Tank height (H)
- 0.5 – 3 m
- Hole height above floor
- 0 – 1 m
- Hole diameter
- 5 – 30 mm
- Tank diameter
- 0.3 – 1.5 m
- Discharge coefficient (Cd)
- 0.6 – 1
How tall the tank is. The tank starts completely full — the water level begins right at the top.
Where the hole is punched in the side wall, measured up from the floor. Must be below the tank height — draining stops once the water level falls to the hole.
A bigger hole drains the tank faster but doesn't change the jet's initial speed — that depends only on how deep the hole sits below the surface.
A wider tank holds more water over the same hole, so it takes longer to drain.
How much a real hole's shape slows the jet down compared to the ideal Torricelli speed. A sharp-edged hole loses the most; a smoothly rounded one loses almost nothing.
About this simulation
What it shows
A full tank drains through a hole in its side. A jet arcs out of the hole while the water level falls.
The key idea
Water leaves at the speed it would have after falling from the surface to the hole, v = √(2gh), so a deeper hole gives a faster jet. As the level drops, the jet slows and the tank empties on a curve.
Try this
Raise Hole diameter from 10 mm to 20 mm: the tank empties about four times faster, but the jet leaves the hole at the same speed.
The hole is assumed small compared with the tank. The discharge coefficient (Cd) covers how the hole's shape slows the jet compared with the ideal case.