Water Bottle Pressure Demo

Materials: ★☆☆ Easy to get from supermarket or hardware store
Difficulty: ★☆☆ Can be easily done by most teenagers
Safety: ★☆☆ Minimal safety procedures required

Categories: Pressure and Fluids

Alternative titles: Three Holed Water Bottle

Summary

By making holes at different heights in a water-filled bottle, students can observe that water squirts out more strongly from the lower holes, demonstrating that pressure increases with depth.

Procedure

Use scissors or a drill to make three small, evenly spaced holes vertically along the side of a plastic bottle.
Cover the holes with tape and fill the bottle with water to the top; screw on the cap.
Place the bottle in a sink or outdoors to contain the water.
Predict how water will flow when the tape is removed — which hole will spray farthest?
Remove the tape and then unscrew the cap to let air replace the escaping water.
Observe that water from the lowest hole shoots out farthest, showing greater pressure at greater depth.

Links

Observing the Effect of Water Pressure - Next Generation Science:

How water pressure changes with depth ~ Water bottle demonstration - Physics Rox by Ms Hoo:

📄 How does pressure change with depth? - Encounter Edu: https://encounteredu.com/take-action/how-does-pressure-change-with-depth

Variations

Try bottles of different sizes to compare the effect of overall height of water.
Use food coloring in the water to make the streams more visible.
Change the liquid (e.g., salt water vs. fresh water) and discuss density effects.
Insert a pressure sensor or force probe at different depths to measure pressure directly.

Safety Precautions

Use child-safe scissors and only under adult supervision.
Conduct outdoors or over a sink to avoid slipping hazards.
Ensure bottle edges around the holes are smooth to prevent cuts.
Handle carefully when removing tape to avoid splashing.

Questions to Consider

Why does the bottom hole produce the strongest stream? (Because pressure increases with depth in a fluid.)
What would happen if you made a hole right at the waterline? (Water would not flow out strongly because pressure difference is minimal.)
How does this principle explain why divers feel pressure on their ears as they descend? (Greater water depth increases the pressure exerted on the body.)
How is this principle important for designing submarines or underwater equipment? (They must withstand increasing pressure as depth increases.)