What is Buoyancy? Buoy = float (in Latin) Archimedes discovered this with the golden crown. (He then ran around buck nekkid!!!)

What is Buoyancy? Buoyancy= “the floating force” Water is “heavier” than the object…so the object floats Low density-more likely to float

What are the units for Buoyancy? Buoyant force is measured in Newtons (N)

What is displacement? Displace = push away The amount of water displaced by an object tells you the volume of that object. The weight of the displaced water is the buoyant force acting on that object.

How much fluid was displaced here?

What is buoyant force? Buoyant force is the upward force of a fluid on an object.

What is a fluid? A fluid is any liquid or gas.

What are the types of buoyancy? Positive buoyancy: Buoyant force is greater than weight so the object floats. Neutral buoyancy: Buoyant force is equal to weight so the object is suspended in the fluid. Negative buoyancy: Buoyant force is less than weight so the object sinks.

When does an object FLOAT? An object will float if the buoyant force is greater than or equal to the weight of object. WEIGHT BUOYANT FORCE

When will an object SINK? An object will sink if the buoyant force of the object is less than than the weight of the object. WEIGHT BUOYANT FORCE

How do you Calculate B F ? Buoyant Force= Weight of displaced fluid OR B F = W air - W water Buoyant = Weight of - Weight of object Force object in air in water

Buoyant Force = Weight of Displaced water When the object is submerged in water, it displaces an amount of water that weighs 3 lbs. Therefore the buoyant force pushing up on the object is 6 cm 3

Buoyant Force = Weight of object in air minus weight of object in water W air = 7 lbs W water = 4 lbs Buoyant Force = 7-4 = 3 lbs Volume of object=Volume of displaced water 6 cm 3

Why do things float? 1. Things float if they are less dense than the fluid they are in. 2. Things float if they weigh less than the buoyant force pushing up on them. 3. Things float if they are shaped so their weight is spread out.

Such as these: Hot air balloons: heat to go up Submarines: fill tanks with air to surface fill with water to submerge

Lowest Mass, Lowest Density, Floats Low Mass, Low Density, Neutral High Mass, High Density, Sink Sub’s carry compressed air tanks to re-fill their ballast tanks Ballast tanks Density

Air Density= 0.04 g/ml Balloon Density = g/ml SINK Density

Air Density= 0.04 g/ml Balloon Density = g/ml NOT MOVING UP OR DOWN Density

Air Density= 0.04 g/ml Balloon Density = g/ml FLOAT

Shape How can you get 5000 pounds of solid steel to float?

Ouch! You know the Buoyant Force.

Soooooooooooo…… A rock has a mass of 76 g and displaced 80 mL of water when it was submerged. What is the volume of the rock? If it displaced a volume of 80mL, then the volume of the rock is 80mL! Or 80 cm3

And………… A volume of 200 mL of water is displaced by a duck that weighs 10N. The weight of the displaced water is 20N. What is the buoyant force on the duck and will it sink or float? B F = 20N The duck will float because 20N (weight of the displaced fluid) is greater than 10N (weight of the duck).

There’s more…….. A little 27g fish displaced a volume of water that weighed 25N. The weight of the fish was 30N. What is the buoyant force on the fish and will it sink or float? B F = 25N The fish will sink because the weight of the fish is greater than the buoyant force.

Some More……. A person weighs 250N while swimming in the dead sea. When outside of the water they weigh 600N. What is the buoyant force acting on them? Will they sink or float? B F = W air – W water = 600 – 250 = 350N The person will float because their weight in the water is less than the buoyant force.

Another????????? A dog jumps into a pool. The water holds him up because he only weighs 10N in water. On land, he weighs 45N. What is the buoyant force? B F = 35N

Observation Time!

Don’t forget your conclusion: