Buoyancy!Buoyancy!

Why Things Float!Why Things Float!

BuoyancyBuoyancy

• The force that acts upwards on an The force that acts upwards on an object, opposite of gravitational object, opposite of gravitational force, on a floating objectforce, on a floating object

• The “push up” on the object (boyant The “push up” on the object (boyant forces) needs to be greater than the forces) needs to be greater than the “push down” pull of gravity on an “push down” pull of gravity on an object or it will not float.object or it will not float.

Buoyancy Cont’Buoyancy Cont’

• The buoyant forces causing an object The buoyant forces causing an object to float are equal in magnitude to the to float are equal in magnitude to the weight of the object (or the volume weight of the object (or the volume of water that it is displacing)of water that it is displacing)

Center of GravityCenter of Gravity

• The center of gravity that is pulling The center of gravity that is pulling down on the boat is the center of the down on the boat is the center of the overall volume of the boat.overall volume of the boat.

• However, the center of gravity However, the center of gravity changes as the boat rocks and rolls changes as the boat rocks and rolls on the water. This can cause on the water. This can cause problems in controlling the boat.problems in controlling the boat.

Archimedes’ StoryArchimedes’ Story

• What did he discover?What did he discover?

• How did he do it?How did he do it?

• What does it have to do with What does it have to do with buoyancy?buoyancy?

• What does it have to do with our What does it have to do with our boat building project?boat building project?