BUOYANT FORCE

buoyant force and fluid pressure

Imagine that you have a glass of ice water in front of you. Take your straw and push down the ice cubes.

What happens to the ice cubes?

A force pushes the ice cubes back up This force is called buoyant force

Buoyant force- the upward force that keeps an object immersed in or floating on a liquid.

BUOYANT FORCE AND FLUID PRESSURE

Water exerts pressure on all sides The pressure on the sides is equal- they

cancel Water pressure pushes down and buoyant

force pushes up. The object goes in the direction of the greatest force (N)

DETERMINING BUOYANT FORCE Archimedes, a Greek mathematician

discovered how to determine buoyant force.

The buoyant force on an object in a fluid is an upward force equal to the weight of the fluid that the object takes the place of, or displaces.

I’m so confused!!

Zach

THE BUOYANT FORCE ON AN OBJECT IN A FLUID IS AN UPWARD FORCE ……..

equal to the weight (N) of the fluid that the object takes the place of, or displaces.

SO HOW DO YOU FIND OUT BUOYANT FORCE? Determine the displacement (volume of the

object)

Then, take the weight of that volume of fluid and change it to Newtons

1 kg = about 10 N (9.8 to be more exact)

The buoyant force = the weight in newtons of the displaced fluid

SINKING An object will sink if its weight is

greater than the buoyant force. For example:

A rock weighs 75N and it displaces 5L of water. So, the weight of the displaced water is 50N.

The rock’s weight is great than the buoyant force, so the rock sinks.

FLOATING An object floats only when the buoyant

force on the object is equal to the object’s weight.

For example: The fish weights 12N and displaces a

volume of water that weighs 12N. Because they are equal, the fish can float

BUOYING UP When the buoyant force on an object is

greater than the object’s weight, the object is buoyed up (pushed up) in water For example:

If a duck dives into water it displaces more than 9N of water, which is the buoyant force. So, the buoyant force on the duck would be greater than the duck’s weight

An object is buoyed up until the part of the object under water displaces an amount of water that equals the object’s entire weight.

SO, WILL AN OBJECT SINK OR FLOAT?That depends on whether the buoyant force is less than or equal to the object’s weight.

REVIEW

An object weights 20N. It displaces a volume of water that weights 15N. What is the buoyant force on the

object? Will this object float or sink? Explain.

VIDEOS http://

www.youtube.com/watch?v=2afDLk-JzEY&feature=related

http://www.youtube.com/watch?v=y0SnFCs9z1g&feature=related

Bill Nye the Science Guy video http://www.youtube.com/watch?v=-U1YVZMifMM&feature=related