What you’ll need
- Two empty 0.5-liter plastic bottles
- A measuring jug with water
- Knife or scissors
- A cutting board
- An awl
- Watercolor paints and paint brush
- A waterproof felt-tipped pen
- A stopwatch
How to do it
- If you look carefully, you’ll notice that the gaps between the markings you made are not exactly equal. The emptier the funnel bottle gets, the closer the gaps. This is because the water flows through the hole faster at the beginning than at the end.
- If the funnel bottle is only half-full, you’ll notice that 30 seconds of flow time do not match up with the markings you made the first time around when the funnel bottle was full: after 30 seconds the first marking still hasn’t been reached.
What's the secret?
It’s not just the size of the hole that determines how quickly the water flows: the shape of the funnel (the top of a bottle) also matters. The water would flow differently if the funnel were cylindrical like a tube or round like a wide bowl. The way the water flows depends mainly on the pressure of the water above the hole. The more water in the container, the higher the pressure above the hole. Logically, the water flows more quickly at the start, when the container is full.