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Build a Levitating Water Fountain with the Stroboscopic Effect

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Can you make water fall up? Or make drops of water hover in mid-air? While you might not be able to make water defy gravity, you can create the illusion that it does using something called the stroboscopic effect. In this project you will make use of the stroboscopic effect to build your own "levitating water" fountain.


Areas of Science
Time Required
Short (2-5 days)
Material Availability
Materials from hardware store or online supplier required.
Low ($20 - $50)
This project requires use of a strobe light. Flashing lights may be unsafe for people with epilepsy or other conditions with sensitivity to light.
Ben Finio, PhD, Science Buddies
The Stroboscopic Effect with Water Drops


Design and build a "levitating water" fountain that can make it look like water drops are frozen in mid-air.


A wooden frame supports tubing over a container of water with a pump inside. An inset photo shows drops of water that look like they are frozen in midair.

The stroboscopic effect is an optical illusion generated by repeated flashes of bright light. To understand the effect, imagine that you are looking at a clock that only has a second hand. The hand completes one revolution every 60 seconds. If you keep your eyes open and look at the clock, you will see the second hand moving forward continuously.

Now imagine that you close your eyes and only open them very briefly at a certain interval.

Figure 1 illustrates these three scenarios.

Three rows, each consisting of five clocks with second hands only.

The first row shows the second hand moving backward by 1 second for each clock, with 59-second gaps indicated between the images. The second row shows the second hand in the same position on each clock, with 60-second gaps indicated between the images. The third row shows the second hand moving forward by one second for each clock, with 61-second gaps indicated between the images.

Figure 1. What you would see if you looked at a clock with a second hand and only briefly opened your eyes every 59 (top), 60 (middle), or 61 (bottom) seconds.

The stroboscopic effect works in a similar manner, except instead of closing your eyes and opening them periodically, you keep your eyes open and the object is illuminated by a bright strobe light that flashes periodically. The number of flashes per second is called the strobe light's frequency. Frequency is measured in hertz (Hz). A frequency of 10 Hz, for example, means that the strobe light flashes 10 times per second.

The period is the amount of time from the beginning of one flash to the beginning of the next flash. You can calculate the period using this equation:

Equation 1:  

So a strobe light with a frequency of 10 Hz has a period of 1/(10 Hz) = 0.1 seconds.

For the stroboscopic effect to work well, the frequency of the strobe light must be above the flicker fusion threshold. This means that the light will flash fast enough that your eye perceives continuous illumination instead of flickering light. Sometimes this effect is also called persistence of vision. If the light flashes too slowly, though, you will see the dark periods in between flashes, and the motion of objects will look jerky.

The stroboscopic effect works for rotating objects like the clock, a fan, or a wheel with spokes, but it also works on a series of falling objects, like a stream of water drops. In this project you will use a strobe light app on your phone to illuminate falling water drops. As explained in this video, the stroboscopic effect can make it look like the water drops are frozen in mid-air, moving up, or falling down very slowly.

Note: Filming objects illuminated by a strobe light is difficult due to something called the rolling shutter effect. You will see this effect as dark bands sweeping across the screen in the video, but you will not see it in person.

For the stroboscopic effect to work well, the frequency of the strobe light should be very close to the frequency of the falling water drops (the number of drops per second). The bursts of light should also be very short. This will result in crisp, clear illumination. If the flashes of light are too long, the drops of water will appear blurry.

The duration of each flash of light is controlled by the strobe light's frequency and its duty cycle. The duty cycle is the percentage of each period that the strobe light is on. Figure 2 shows two flashing patterns, both at 10 Hz (meaning they flash 10 times per second, and they have a period of 0.1 seconds).

The first pattern has a duty cycle of 50%, so the strobe light is on for half of each period and off for half of each period (0.05 seconds each). The second pattern has a duty cycle of 10%, so the strobe light is only on for 10% of each period (0.01 seconds) and off for 90% of each period (0.09 seconds).

For this project it is important to find an app that lets you adjust both the frequency and the duty cycle of the strobe independently. Some strobe light apps might only let you control the frequency.

Diagram of two rectangular waveforms showing how the strobe light alternates between ON and OFF. In one the ON and OFF sections are equal length, representing a 50% duty cycle. In the other, the ON section is much shorter than the OFF section, representing a 10% duty cycle. Both waveforms are at 10 hertz, which means they have 10 periods in one second.
Figure 2. Top: A strobe pattern with a frequency of 10 Hz and a duty cycle of 50%. Bottom: A strobe pattern with a frequency of 10 Hz and a duty cycle of 10%.

Now that you understand the stroboscopic effect, frequency, and duty cycle, you are ready to build your own "levitating water" fountain!

Terms and Concepts



Materials and Equipment

Note: this is an engineering design project. You will decide how to build your "levitating water" fountain, so the project does not have an exact list of materials. If you have a question about materials for this project, you can ask on our Ask an Expert forums.

Disclaimer: Science Buddies participates in affiliate programs with Home Science Tools, Amazon.com, Carolina Biological, and Jameco Electronics. Proceeds from the affiliate programs help support Science Buddies, a 501(c)(3) public charity, and keep our resources free for everyone. Our top priority is student learning. If you have any comments (positive or negative) related to purchases you've made for science projects from recommendations on our site, please let us know. Write to us at scibuddy@sciencebuddies.org.

Experimental Procedure

Note: This engineering project is best described by the engineering design process, as opposed to the scientific method. You might want to ask your teacher whether it's acceptable to follow the engineering design process for your project before you begin. You can learn more about the engineering design process in the Science Buddies Engineering Design Process Guide.

Strobe Light Warning

Strobe lights may not be safe for people with epilepsy or other conditions with sensitivity to light.

Build Your Levitating Water Fountain

Build the experimental setup as shown in Figure 3 and described in the following steps. You can also watch this video for an overview of how to build the fountain. Remember, however, that this is an engineering design project, so your fountain does not have to look exactly like the one shown in the video.

DIY Levitating Water Drop Fountain

A handmade fountain built on a wooden frame.

The fountain has a rectangular plywood base and a vertical piece of wood with a horizontal piece extending to one side at the top. The frame supports tubing that is connected to a pump sitting in a container of water at the base. A C-clamp is placed over the tubing at the top of the frame. The end of the tubing is aimed down so water will drip back into the container.

Figure 3. A homemade "levitating water" fountain.
  1. Build a frame to support the tubing about one foot above a container of water. The frame can be made from scrap wood or other materials. Tip: Do not use cardboard, paper, or other materials that will lose their strength if they get wet, since the water tends to splash.
  2. Fill a container of water and place it at the bottom of the frame.
  3. Read the instructions for your pump. Some pumps are "submersible," meaning they are designed to be submerged in water, and other pumps are not. Some pumps are "self-priming," meaning they can initially suck water up through a tube, and others are not. This will determine where you place your pump. You might need to place the pump directly in the container of water, or you might need to place it next to the container with a tube going into the water.
  4. If needed, attach tubing to the inlet nozzle of your pump and run it into the container of water.
  5. Attach tubing to the exit nozzle of your pump, run it up along the frame, and point the end down into the container of water. Attach the tubing to the frame with tape to hold it in place. Tip: Small diameter tubing (about 1/8 inch) works well to create drops of water. If your pump has a larger nozzle, you can step down to smaller diameter tubing using adapters or pieces of tubing that fit inside each other (Figure 4).

    A pump with three tube segments of different diameters.

    The pump outlet attaches to the widest tube piece, which attaches to a medium-diameter piece, which attaches to a narrow tube the right size to create a stream of water droplets.

    Figure 4. An intermediate piece of tubing used as an adapter to step down from the larger-diameter pump nozzle to smaller tubing. The largest piece of tubing is 5/16 inch ID and 7/16 inch OD. The middle piece of tubing is 3/16 inch ID and 5/16 inch OD. The smallest piece of tubing is 1/8 inch ID and 3/16 inch OD. The inner diameter of one piece matches the outer diameter of the next piece.
  6. Make sure your pump is ready to pump water. (It should either be submersed in water or have a tube going into the water, depending on the type of pump.) Caution: Some pumps can overheat and be damaged if they run without water flowing through them.
  7. Connect the power supply to your pump. How you connect them will depend on the pump and power supply you purchased. Figure 5 shows one example. Your pump may have a red wire or a "+" sign to indicate the positive connection. The two wires of the wall adapter are stripped and connected to the pump's wires with alligator clips. Be careful, as your pump will turn on as soon as you connect the power supply. Tip: If your pump runs in reverse (it does not appear to suck up any water, or it blows bubbles into the water), or if does not run at all, the positive wire of your pump might be connected to the negative wire of your power supply. To correct this, switch the positive and negative wires.)

    A DC wall adapter with two wires connected to a pump with two wires using two alligator clip leads. Red and black leads are used to indicate positive and negative, respectively.
    Figure 5. A pump's wires connected to the wires from a 12 V wall adapter. Red and black indicate the positive and negative wires, respectively.
  8. Watch the water flowing out of the tubing. If the water comes out as a rapid series of drops, you are ready to move to the next section. If the water seems like a jet or continuous stream, you need to slow the water flow down. Place a C-clamp over the tubing as shown in Figure 6. Tighten the clamp to adjust the water flow rate until it falls as a rapid series of drops.

    A c-clamp squeezes the tubing against the wooden frame in order to reduce water flow.
    Figure 6. C-clamp placed over tubing to control the water flow rate.

Test the Stroboscopic Effect

Now that you have finished building your fountain, it is time to test it and fine-tune it to generate the "levitating water" illusion.

  1. Turn off all the lights in the room and close any window curtains or blinds.
  2. Turn on your pump.
  3. Open the strobe light app on your phone. Set the duty cycle to 10% and the frequency to about 30 Hz.
  4. Aim your phone at the water drops from the front. Slowly start increasing the frequency, 1 Hz at a time.
  5. Watch the water drops carefully. Which way do they appear to be moving? Does their apparent speed or direction change as the frequency of the strobe changes?
  6. Keep increasing the frequency of the strobe. If you see an illusion, does it disappear at some point?
  7. Continue to adjust the frequency. Can you find frequencies where the water drops appear to
    1. Move up slowly?
    2. Move down slowly?
    3. Hover in place?
  8. If needed, you can also try adjusting the frequency of the water drops by tightening or loosening the C-clamp. Tightening the clamp should lower the frequency (fewer drops per second) and loosening the clamp should increase the frequency (more drops per second). If you have trouble getting the illusion to work just by adjusting the strobe light, try adjusting the clamp, then try testing different strobe frequencies again.
  9. There are other things you can adjust to change the appearance of your fountain.
    1. If the room is still somewhat bright (for example, daylight is leaking in around curtains), try running the fountain at night.
    2. Try changing the angle at which you illuminate the water drops. What happens if you hold your phone above or to the side of the drops instead of in front of them? Just be careful not to drop your phone in the water!
    3. Try changing the background color of the fountain by putting it in front of a different-colored wall or by holding a piece of posterboard or other material behind it.
  10. Keep adjusting your fountain until you think you have the best conditions for your illusion. Then you are ready to show off your fountain to family or friends, or at a science fair! Can you convince people that water drops are falling up or hovering in mid-air? Can people figure out how the illusion works?
icon scientific method

Ask an Expert

Do you have specific questions about your science project? Our team of volunteer scientists can help. Our Experts won't do the work for you, but they will make suggestions, offer guidance, and help you troubleshoot.


  • Can you make a video of your fountain? Note that filming the stroboscopic effect can be tricky. You will probably need to manually adjust the camera settings instead of leaving it in automatic mode. Experiment until you find the settings that work best. Your phone might not let you run the strobe light app and use the camera at the same time, so you might need a separate phone or camera to film. Even then, the light from the strobe app on your phone might not be bright enough to record a good video. You could use a separate stroboscope, which will be much brighter. Stroboscopes are expensive, so see if you can borrow one from a science teacher at your school. You can also build your own brighter strobe light (see next point).
  • You can build your own much brighter, strobe light using LED strips and an Arduino. You can program the Arduino to flash the LEDs at a specified frequency and duty cycle. See the RGB Time Fountain video for an example. This project will require prior experience with an Arduino or willingness to learn. See the Science Buddies How to Use an Arduino resource for help.
  • Can you try out the stroboscopic effect on a rotating object, like a fan or wheel?


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General citation information is provided here. Be sure to check the formatting, including capitalization, for the method you are using and update your citation, as needed.

MLA Style

Finio, Ben. "Build a Levitating Water Fountain with the Stroboscopic Effect." Science Buddies, 29 Apr. 2023, https://www.sciencebuddies.org/science-fair-projects/project-ideas/Phys_p120/physics/stroboscopic-effect-levitating-water-drops. Accessed 6 Dec. 2023.

APA Style

Finio, B. (2023, April 29). Build a Levitating Water Fountain with the Stroboscopic Effect. Retrieved from https://www.sciencebuddies.org/science-fair-projects/project-ideas/Phys_p120/physics/stroboscopic-effect-levitating-water-drops

Last edit date: 2023-04-29
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