What it shows
Water squirts furthest from the lowest hole in a bottle, because the weight of all the water above it presses on it. Pressure in a liquid increases with depth, which is why dam walls are thickest at the bottom.
The science
Every layer of water in the bottle has to carry the weight of all the water above it, so the deeper you go, the harder the water presses on the walls. At a hole, this pressure pushes the water out, and a bigger push gives a faster jet that travels further before it falls. The top hole has only a little water above it and gives a weak, short jet. This rule is the same in a lake or the sea, which is why divers feel pressure on their ears as they go down.
Materials
Cost: free. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- A 1 or 2 litre plastic bottle (free)
- A nail or a pin to make three holes, used by an adult
- Tape to cover the holes while filling
- A jug of water and a tray or a place outdoors
- A ruler and chalk to mark where each jet lands
Safety
For this project: An adult must make the holes with a heated nail or a sharp pin. Do the experiment outdoors or on a tray.
Never use mains electricity: power models with cells, batteries or a low-voltage adapter. Sharp and hot tools, flames and lab chemicals need an adult or your teacher beside you. Keep magnets, button cells and small parts away from young children, and wash your hands after making.
All the safety rulesStep by step
8 steps. Do them in order, and test each part before you go on to the next. Write what you notice in a notebook as you go.
Ask an adult to make three holes of the same size in a straight line up the side of the bottle, at about 5 cm, 12 cm and 19 cm from the bottom.
Cover all three holes with a single strip of tape and fill the bottle with water to the top.
Stand the bottle at the edge of a table or step so the jets have room to fall, with the tray or the ground below.
Pull the tape off quickly and watch the three jets; the bottom jet shoots furthest and the top jet barely dribbles.
Mark with chalk where each jet lands and measure the distance from the bottle with the ruler.
Refill and repeat twice to check the pattern is the same each time.
Let the water level fall and notice that all the jets get shorter as the bottle empties.
Write a table of hole height against jet distance and draw a labelled sketch of the jets.
What you should see
Three clear jets of different lengths: the lowest hole throws water the furthest and the highest hole the least, and all the jets shorten as the level drops.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
1Why does the bottom hole squirt the furthest?
It has the most water above it pressing down, so the pressure there is greatest.
2What happens to the jets as the bottle empties?
They get shorter because there is less water above each hole.
3Why are dam walls thicker at the bottom?
The water pressure is greatest at the bottom, so the wall must be strongest there.
4Does the pressure depend on the width of the bottle?
No, only on the depth of water above the hole.
Take it further
Make a second bottle with three holes at the same height round its sides and show that the jets are all equal, so pressure acts equally in all directions at the same depth.
Change one thing, measure what happens, and add a table or chart of your readings: that is what turns a model into your own investigation.
Free ebooks for this project
Science projects
Best Out of Waste Science Projects
Working models from bottles, cardboard, CDs and old parts
Science projects
Easy Science Projects for Class 1 to 5
Simple, safe projects young children can make with a little help