Science Buddies: "Ask an Expert"

Hello everyone,

I am trying to conduct an experiment on density and buoyancy of a toy boat. I have read about Archimedes Principle, buoyancy and density but am still a bit unsure on how to tackle my experiment. In my design lab we are instructed to provide an independent variable and a dependent variable. I was thinking of constructing a toy boat out of Styrofoam and letting it float on a tub of water, then changing the total mass of the boat by adding weights. I know that the density of the object will obviously change.

My independent variable would be : the total mass of the toy boat
Dependent Variable: The force of buoyancy on the boat? The surface area of the boat? The total depth and volume occupied by the boat?

Please help and I would love to hear some feedback. If you guys have any recommendations for an easier project (I need to change something) please recommend them. I'm not very bright at Physics and would appreciate all the help you could provide. Thank you!

Hello pdesco,

I think you've outlined an interesting experiment and you've correctly identified a good independent variable. Dependent variables respond to changes in the independent variable. So, dependent variables could be the buoyancy force or the volume displaced by the boat (which could be used to find the buoyancy force). The surface area of the boat might be another independent variable to consider. It's another factor that can change buoyancy.

If you want some additional ideas there is a project on this website that explores buoyancy factors including weight, shape and surface area:

https://www.sciencebuddies.org/science- ... ml#summary


I hope this helps. Please ask again if you have more questions.

A. Norman

Hello norman40,

Thanks for the help. This made it clear. I saw the website link and found some helpful comparisons. My question is: if the dependent variable is the volume displaced by the boat -- assuming that I could calculate for the buoyancy force using a corresponding formula -- would I be calculating the changing volume using the same method as instructed by the Website?

Hello pdesco,

For the project described at this link:

https://www.sciencebuddies.org/science- ... ml#summary

the independent variables are boat volumes and “cargo weight” (pennies added to the boats). The dependent variable is the weight needed to sink the boats.

This project demonstrates that a boat will float if its density (including cargo) is less than the density of water. You could add a tabulation of the buoyancy forces for the boats. The buoyancy force will equal to the weight of water displaced by a floating boat.

A simple way to find the amount of water displaced would be to measure the depth of the boat in the water. With the depth and the area of the hull, you can calculate the volume displaced. With the volume displaced and the density of water you can calculate the weight of water displaced. An example is shown at this link:

https://www.boundless.com/physics/textb ... -344-5623/


I hope this helps. Please post again if you have more questions.

A. Norman