Department of Energy Argonne National Laboratory Office of Science NEWTON's Homepage NEWTON's Homepage
NEWTON, Ask A Scientist!
NEWTON Home Page NEWTON Teachers Visit Our Archives Ask A Question How To Ask A Question Question of the Week Our Expert Scientists Volunteer at NEWTON! Frequently Asked Questions Referencing NEWTON About NEWTON About Ask A Scientist Education At Argonne Buoyancy and Bubbles

Name: Mmaryam
Status: student
Grade: 9-12
Country: Nigeria
Date: Winter 2011-2012

How does the buoyancy of an object depend on the presence of bubbles?

On the whole, bubbles reduce the density of water and reduce buoyancy. In fact, in teaching sailing classes we were told to warn small boat sailors about getting too close to the back of large ships and their wakes. The air bubbles in the wake close to the stern of the ship could cause real buoyancy problems!

R. W. "Mr. A." Avakian

The buoyancy of an object depends upon the mass of the volume of the fluid displaced. Since bubbles have a large volume per unit mass, they displace a lot of the fluid. This makes the object appear a lot lighter if bubbles are attached.

Vince Calder


An object will float if it weighs less than the water it displaces.

So if I put an object in a bucket that is filled to its very top with water Then collect and weight all of the water that spills over the side of the bucket, Then if the object weighs less than the spilled water, the object will float. If the object weighs the same as the spilled water it will neither sink nor float, it will just hang there And if the object weighs more than the spilled water, it will sink.

Bubbles in an object that is underwater displaces water but weighs nothing. So in that way, bubbles effect the buoyancy of an object.

US Navy submarines have ballast tanks. When they want to dive, they fill the ballast tanks with water until the submarine weighs more than the water it displaces. When they want to surface they blow compressed air into the ballast tanks which expels the water from the ballast tanks and causes the submarine to weigh less than the water it displaces and the submarine floats to the top of the water.

Sincere regards, Mike Stewart

Click here to return to the Physics Archives

NEWTON is an electronic community for Science, Math, and Computer Science K-12 Educators, sponsored and operated by Argonne National Laboratory's Educational Programs, Andrew Skipor, Ph.D., Head of Educational Programs.

For assistance with NEWTON contact a System Operator (, or at Argonne's Educational Programs

Educational Programs
Building 360
9700 S. Cass Ave.
Argonne, Illinois
60439-4845, USA
Update: June 2012
Weclome To Newton

Argonne National Laboratory