Jump to main content

Make a Straw Siphon

1
2
3
4
5
1 review

Summary

Active Time
10-20 minutes
Total Project Time
< 10 minutes
Key Concepts
Gravity, pressure, energy
Credits
Ben Finio, PhD, Science Buddies
Make a Straw Siphon

Introduction

What's an easy way to move liquid from one place to another? A siphon! With just a little effort to get it started, you can then sit back and watch liquid flow from one container to another, as it seemingly defies gravity by going uphill. Try this activity to make your own simple siphon using straws.

This activity is not recommended for use as a science fair project. Good science fair projects have a stronger focus on controlling variables, taking accurate measurements, and analyzing data. To find a science fair project that is just right for you, browse our library of over 1,200 Science Fair Project Ideas or use the Topic Selection Wizard to get a personalized project recommendation.

Materials

  • Flexible drinking straws
  • Scissors
  • Electrical tape or modeling clay
  • Tall glass or container
  • Shorter glass or container
  • Water
    Materials for straw siphon science experiment

Prep Work

Do this experiment in an area where you can easily clean up spills. You may want to work in a large pan, baking tray, or other shallow container.

Instructions

  1. Fill your tall container to the brim with water and place it next to your small container.
  2. If needed, cut the long end of a straw so it fits into your tall container, with the flexible part resting on the lip.
  3. Place the long end of the straw into the tall container of water.
    Think about:
    Does anything happen?
  4. Remove the straw from the water.
  5. Now, place your finger over the short end of the straw.
  6. Quickly put the long end of the straw into the tall container, then release your finger.
    Think about:
    What happens this time?

    A drinking straw siphoning water out of a plastic cup into a shallow container.
  7. Keep watching the siphon.
    Think about:
    When does the water stop flowing?
  8. Refill your tall container with water.
  9. Now try to make a longer siphon that can move more of the water.
  10. Cut off the long part of a straw.
  11. Cut one end to make a point.

    The end of a straw cut to make a point.
  12. Push the point into the short end of another straw.

    The pointed end of one straw inserted into the end of another straw.
  13. Seal around the connection with tape or modeling clay.

    Two straws joined and connected with electrical tape.
  14. Now, repeat the process you followed earlier. Cover one end of the straw with your fingertip. Quickly put the other end in the tall container and release your finger.
    Think about:
    What happens this time? How much water flows into the shorter container?

    Two connected straws siphoning water from a tall cup to a shorter container
  15. Note: if you get air bubbles in the straw and the water stops flowing, you do not have a good seal around the connection between the straws. Try re-applying your tape or pressing the modeling clay on more firmly. Make sure there are no gaps where air could get in.
  16. Do you think you can start the siphon without covering one end with your finger? Check out the Self-Starting Siphon activity to find out!

Cleanup

Wipe up any spills.

What Happened?

When you put the single straw into the tall container and release your finger, water should shoot up over the top, then start flowing down into the other container. The water will stop flowing once the water level in the tall container reaches the same height as the other end of the straw. When you make a longer siphon (so the end in the short container is underwater instead of suspended in the air), the water will keep flowing until the water levels in the two cups are equal. Read the Digging Deeper section to learn more about how siphons operate.

Digging Deeper

The physics of a siphon can seem confusing and even counterintuitive at first. We all know that water flows downhill. It would be no surprise if you just poked a hole in the side of the taller container and water spilled out into the lower container. But a siphon requires water to go uphill first, going against gravity, before flowing down into the lower container. Because of this, the siphon needs a little help to get started. One way to do this is to suck the liquid through the straw. That is OK with water, but it is certainly a bad idea with a poisonous liquid like gasoline (so if you ever see someone do that in a movie or on TV—it is not safe!). Instead, in this activity, you plugged one end of the straw with your finger. This prevents air from escaping the straw, and therefore prevents water from entering the straw when you first insert it into the water. When you quickly release your finger, water shoots up the straw, and it has enough energy to make it over the top. Once the water starts flowing, it will keep going until the water levels in the two containers are equal (or, if the siphon's exit is above water, until the water level in the tall container is at the same height as the exit—this is explained by something called Bernoulli's Equation). The water in the second container can never get higher than the first container, because this would violate conservation of energy. That would be like a ball rolling up a hill all by itself!

icon scientific method

Ask an Expert

Curious about the science? Post your question for our scientists.

For Further Exploration

  • Does the height of the siphon's inlet matter? What happens if you hold the straw and keep the inlet just below the surface of the water in the tall container, instead of at the bottom? Does your siphon still work?
  • Does the shape of your siphon matter? What happens if you connect more bendy straws or use flexible tubing to add loops to the middle of your siphon?
  • Can you make a self-starting siphon that does not require you to cover one end with your finger? Check out the Self-Starting Siphon Activity to find out!

Activities

    STEM Activity
    1
    2
    3
    4
    5
    4 reviews
    Have you ever used a crazy straw? Some spiral their way up. Others have fancy colors or decorations. Some are thin and others are wide. But just about all of them leave you sipping your drink from about the same distance. Why? Wouldn't it be fun to poke your head out of an upstairs window and secretly take a sip from a drink way below? Would it even be possible? With this activity, you'll see if you can set your own record for the longest working straw! Read more
    STEM Activity
    1
    2
    3
    4
    5
    3 reviews
    Have you ever wondered how a musical instrument produces the beautiful sounds that it does? To make a certain note, the instrument has to make a certain sound wave. Depending on the instrument, the sound wave that is made can be affected by changing the length of part of the instrument, such as the strings in a piano or on a guitar, or a trombone’s air column. In this science activity, you will make your own musical instruments using drinking straws and explore how changing the length of the… Read more
    STEM Activity
    If you have ever seen someone use a siphon in a movie, they probably sucked on the tube to get it started. That can be dangerous with liquids like gasoline! Can you make a siphon that will start on its own? Try this activity to find out! Read more

Careers

Career Profile
When you think about a city that is a great place to live, what do you consider? Probably a community where the citizens are happy, healthy, and comfortable. Part of being all three is having a clean, safe, and constant water supply. Many of us take for granted that when we turn the faucet on we will be able to get a glass of water or that when we flush the toilet our waste will be carried away and treated somewhere. Well, that is what a water or wastewater engineer does. Their job is to design… Read more
Career Profile
Physicists have a big goal in mind—to understand the nature of the entire universe and everything in it! To reach that goal, they observe and measure natural events seen on Earth and in the universe, and then develop theories, using mathematics, to explain why those phenomena occur. Physicists take on the challenge of explaining events that happen on the grandest scale imaginable to those that happen at the level of the smallest atomic particles. Their theories are then applied to… Read more

Reviews


|
Science Buddies |
Was this review helpful?

Top
Free science fair projects.