The Effect of a Bubble’s Radius on the velocity it Rises: Introduction | Procedure and Design | Problem | Hypothesis | Data | Conclusion | Bibliography | Other Links | Go Up

Natasha Arnan, Nicole Hebda

Physics IA


Introduction | Top

            Why do hot air balloons float? Why do boats float? Why do bubbles rise? All these things occur because of buoyancy. Buoyancy was discovered by Archimedes, a Greek mathematician and physicist, in 212 BC. Buoyancy is the lifting force on an object submerged in a fluid. When the object is less dense than the fluid surrounding it, the object rises. For example, air is less dense than corn syrup; hence, air bubbles rise through corn syrup.

            Another important aspect that goes hand in hand with buoyancy is viscosity. Viscosity is a physical property that characterizes the flow resistance of simple fluid. Isaac Newton was the first person to discover viscosity. It helped further differentiate fluids by physical properties (Newtonian and Non-Newtonian fluids).

            We were intrigued by both of these concepts, so we wanted to incorporate them into our experiment. Being able to find the buoyant force of the bubbles that we created while putting into account the viscosity of our fluid, we investigated the relationship of the radius and velocity of an air bubble in a fluid with high viscosity (corn syrup). We wanted to use a fluid that has a higher viscosity because we wanted the bubble to rise slower in order to more accurately calculate its measurements. This would, not only, show us the relationship of both, but watching the bubbles rise to the surface of the corn syrup fulfilled our childhood expectations of what blowing bubbles into our drinks is supposed to look like. Our experiment should be posted on an oddly satisfying instagram account.


Procedure and Design | Top


     Corn Syrup (1.131*10^-4 m^3)

     Beaker (holds 240 ml)

     12 inch metal ruler

     Twisty orange straw

     iPhone 8 camera

     A paper towel to catch possible messes


Untitled drawing.jpg



We started to collect our materials in order to set up our experiment. We began to search for the perfect clear container that was small enough for the amount of corn syrup that we had and big enough for us to see the bubbles that we create. After we filled the 240 ml beaker with corn syrup, we tested out straws of different sizes: wide and thick, regular, and twisty and skinny. We found that the twisty and skinny straw worked best for our beaker because it created bubbles that were small enough for it to not be deformed and for us to be able to find the velocity. We used corn syrup because the density caused the bubbles to rise slower than other clear consistencies, corn syrup allowed us to be able to measure the bubbles.

We started the experiment by pouring corn syrup in a 240 ml beaker. One of us held up a 12 inch ruler right next to the beaker in order for us to measure the radius of the bubbles and the other used an iPhone 8 to take a video with the ruler and beaker in the shot. The one holding the ruler was also using the twisty orange straw to blow consistent bubbles in the corn syrup. We did multiple takes in order to blow the most consistent and easily readable bubbles. In order to get the most accurate measurements of the radi, we downloaded the videos to a Mac and zoomed into the video find the most precise measurements with the ruler in the video. We also used all the measurements that we found to try to find an accurate measurement of the viscosity of corn syrup.


In our experiment, we tested how the radius bubbles affects the velocity they rise through corn syrup at. The independent variable in our experiment was the radius of the bubble. We blew bubbles of various sizes through a straw to get 15 data points. The dependent variable in our experiment was the velocity the bubbles rose through the corn syrup at. We analysed a video of the bubbles rising to determine both the radius of each bubble and their velocity. Variables that remained constant in our experiment were the beaker we used, the camera we used to film, and the way we timed the experiment. To maintain the time measurement we used to find the velocity, we started an iphone timer right when the bubble came out of the straw and stopped it when the top edge of the bubble reached the top of the corn syrup. Our times are rounded to the hundredth place.



Statement of Problem | Top

The purpose of this experiment is to find the relationship, if any, between the radius of a bubble and the velocity that it rises in corn syrup.


Hypothesis | Top

If the radius of the air bubble in the corn syrup increases, then the velocity of the air bubble will increase because the volume of the displaced fluid (or air bubble) increase therefore increasing the buoyant force going up. In other words, there is more fluid that is displaced with a larger bubble, making it rise faster in a container of fluid that has a higher density than air.




Data | Top






















Data File: Text / Excel



Conclusion | Top

            The results of our experiment demonstrate that a larger radius increases the velocity of the air bubble. Our results supports our hypothesis, making it a valid statement. To prove that our hypothesis was correct, we used the scientific equation of the buoyant force in order to find our results.

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            We noticed that the volume displaced is our air bubble and by increasing the volume displaced (or creating a larger bubble) we are increasing the buoyant force, therefore if the buoyant force is increasing, the velocity is increasing as well. Because we used one fluid, the density is constant, while gravity is constant as well. As both of these variables are constant, it is evident that the volume displaced controls the buoyant force of this experiment, therefore the radius increases the velocity. A larger radius means greater volume displaced, and a greater buoyant force means the bubble has a faster velocity.

            However, besides using the equation to validate our findings, we first measured the time and radius of each air bubble that we created. By finding the time and radius, we found each of the bubbles’ velocities (radius/time). As we found the velocity, we created a graph with our findings. The trend line of our graph is increasing, justifying that our hypothesis is correct using the data we collected.The increasing trend line means that a larger air bubble radius means a larger velocity.

            Our experiment had many limitations. First, the shape of the bubbles was somewhat unpredictable. Some of the bubbles were much more oval shaped that sphere shaped. Also, our timing may have been a little off due to human error. In our experiment, being off by a small amount when timing could have a drastic impact on our results. Third, our data did not have a huge amount of variation. The radii of the bubbles did not have a huge amount of variation which led the velocities to have little variation. Lastly, our experiment was filmed on an iPhone camera so when zooming in to find the radius of the bubbles, the video quality left the image pixelated and somewhat difficult to decipher.

            One way to improve our experiment would be to have a longer distance for the bubbles to travel so they could become more spherical. Additionally, we could have had a timer in the video of the experiment so we wouldn’t have to rely on a person to time the bubbles after. Also, we could have had a larger variety of straws and a bigger beaker in order to have a wider range of radii. Lastly, having a higher quality video would make it easier to zoom in and find the radii of the bubbles.


Bibliography | Top

“Buoyancy.” The Columbia Encyclopedia, 6th Ed,, 2019., 5 Feb. 2012.

“Buoyancy – The Physics Hypertextbook.” Free Fall – The Physics Hypertextbook.

Engrraihan. “What Is Viscosity ? States Newton's Law of Viscosity & Define Newtonian and Non-Newtonian Fluid.” Mechanical Engineering, 30 Jan. 2016.

“What Is Buoyant Force?” Khan Academy, Khan Academy.


Links | Top

This website explains buoyancy and equations:

This website explains buoyancy with respect to the Archimedes Principle:

This website explains the relation between size and speed of a bubble:

This website explains viscosity:

This website talks about finding the velocity of a bubble: