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Review

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**Which of the states of matter are fluids?**

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**Which direction are the particles going to flow?**

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**Name some examples of fluids going from high pressure to low pressure**

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**All fluids exert pressure**

Equation? Force Area Pressure =

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**What happens to air pressure as you go up?**

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**What happens to water pressure as you go up?**

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Buoyant Force

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Buoyant force the upward force that fluids exert on all matter

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There is more pressure at the bottom of an object because pressure increases with depth. This results in an upward buoyant force on the object

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**Archimedes Greek Mathematician 267-212 B.C.**

Discovered how to determine buoyant force

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**Archimedes’ principle**

the buoyant force of an object is equal to the weight of the fluid displaced by the object

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**the buoyant force of an object is equal to the weight of the fluid displaced by the object**

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**The weight of the object does not affect buoyant force**

Only the weight of the displaced water determines the buoyant force on an object

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Weight does not determine the buoyant force, but it does determine whether the object will sink or float

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**An object will sink if its weight is greater the buoyant force**

Sinking An object will sink if its weight is greater the buoyant force 12 N 5 N

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**An object will only float if its weight is equal to the buoyant force**

Floating An object will only float if its weight is equal to the buoyant force 12 N

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**Floating 9 N Buoyant force is equal to the weight**

Only the feet, legs, and stomach have to be underwater to displace 9 N of water which is equal to the duck’s weight 9 N

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Buoying Up If the duck dove underwater, it would displace more than 9 N of water…

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Lab Time!!!

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Why does the rock sink? Weight of rock is greater than the weight of the water it displaced! Mass is proportional to weight so the rock has more mass per volume than the water does.

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Density Mass per unit volume

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Sinking Objects that are more dense than the surrounding fluid will sink

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Floating Objects that are less dense than the surrounding fluid will float

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**Steel is almost 8 times denser than water… so how does it float?**

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**Changing Overall Density**

Mass Volume Shape

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MASS

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MASS When water is added to the ballast tanks of a submarine, the mass increases so the density also increases. When water is removed, mass decreases so density decreases

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Chambered nautilus Can fill or empty their chambers with water to control buoyancy

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VOLUME Inflated swim bladders in fish create more volume so the density decreases

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Swim bladder Controls buoyancy Dar

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Puffer fish

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SHAPE a hollow shape increases the volume so the density decreases

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**An object weighs 20 N. It displaces a volume of water that weighs 15 N.**

What is the buoyant force on the object? Will this object float or sink?

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**What is the density of an object that has a mass of 150 g and a volume of 50 cm³?**

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**Iron has a density of 7. 9 g/cm³**

Iron has a density of 7.9 g/cm³. Mercury is a liquid with a density of 13.5 g/cm³. Will iron float or sink in Mercury?

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