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Science project idea

Water siphon from a kitchen tube: height difference and flow rate

A siphon moves water up and over a barrier without a pump, because the longer falling column of water pulls the liquid along. You measure how the height difference between two buckets changes the flow rate.

Make it yourself8 numbered steps, the materials and the science, all free.Go to the stepsGet a ready-made kitReady-made models, kits and spare parts in the store under Physics.Browse PhysicsAsk on WhatsAppAsk the head office whether a model or kit for this idea is available.Send a message

What it shows

A siphon moves water up and over a barrier without a pump, because the longer falling column of water pulls the liquid along. You measure how the height difference between two buckets changes the flow rate.

The science

Once the tube is full of water, atmospheric pressure pushes water into the upper bucket end, and the weight of the longer, falling column pulls water through the bend. The flow speed depends on the height difference between the water surface and the outlet. If air enters the tube, the column breaks and the flow stops.

Materials

Cost: under Rs 200. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.

  • A clear plastic tube about 1 metre long (garden or aquarium tube)
  • Two buckets or large containers
  • A stack of books to raise one bucket
  • A measuring jug
  • A stopwatch
  • A ruler
  • Water

Safety

For this project: Do not suck on the tube to start the siphon; fill it with water by dipping instead. Mop up spills so the floor is not slippery.

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 rules

Step 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.

  1. Place the full bucket on the books and the empty bucket on the floor.

  2. Fill the tube completely with water by dipping it in a bucket, and pinch both ends shut with your fingers.

  3. Put one end under the water in the top bucket, and the other end in the lower bucket below the level of the water.

  4. Release the fingers and watch the water flow without any pumping.

  5. Measure the vertical drop between the water surface and the outlet end in centimetres.

  6. Collect water for ten seconds in the jug and calculate the flow in ml per second.

  7. Change the height difference by adding or removing books and repeat for at least five heights.

  8. Plot a graph of flow rate against the height difference.

What you should see

The water flows through the tube without a pump, and the flow gets faster as the height difference rises. The flow stops when the outlet is raised level with the water surface.

Viva questions

A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.

1What makes a siphon work?

Atmospheric pressure and the weight of the longer water column.

2Why must the tube be full of water?

Air breaks the column and stops the flow.

3When does the flow stop?

When both water levels are equal.

4Where are siphons used?

Emptying tanks and aquariums.

Free ebook: Viva Questions for Science Projects

Take it further

Try tubes of different widths and see how the diameter affects the rate.

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

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