Density & Density & BuoyancyBuoyancy

DensityDensityDensity = Mass/VolumeDensity = Mass/Volume

What is the SI Unit for Mass? Volume?What is the SI Unit for Mass? Volume?

SI Unit for Density = kg/mSI Unit for Density = kg/m33

Also…g/cmAlso…g/cm3 3

g/ml and kg/Lg/ml and kg/L

The Density of Water = 1 g/cmThe Density of Water = 1 g/cm33

Important to Remember…1 mL = 1 Important to Remember…1 mL = 1 cmcm33

What is density?What is density?

Density = Density = mass mass OR mass ÷ OR mass ÷ volume.volume.

volumevolume

You can also rearrange the formula and solve for mass or You can also rearrange the formula and solve for mass or

volume.volume.

Volume = mass/densityVolume = mass/density

Mass = volume x densityMass = volume x density

ALWAYS REMEMBER

UNITS!

Let’s try a density Let’s try a density problem togetherproblem together

Frank has a paper clip. It has a mass of Frank has a paper clip. It has a mass of 9g and a volume of 3cm9g and a volume of 3cm33. What is its . What is its density?density?

Frank also has an eraser. It has a mass Frank also has an eraser. It has a mass of 3g, and a volume of 1cmof 3g, and a volume of 1cm33. What is its . What is its density?density?

Work on these problems with your Work on these problems with your neighbor.neighbor.

Jack has a rock. The rock has a mass Jack has a rock. The rock has a mass of 6g and a volume of 3cmof 6g and a volume of 3cm33. What is . What is the density of the rock?the density of the rock?

Jill has a gel pen. The gel pen has a Jill has a gel pen. The gel pen has a mass of 8g and a volume of 2cmmass of 8g and a volume of 2cm33. . What is the density of the rock?What is the density of the rock?

Now, try these on your Now, try these on your own.own.

Al’Licia has a watch. It has a mass of Al’Licia has a watch. It has a mass of 4g and a volume of 2cm4g and a volume of 2cm33. What is the . What is the density of the watch?density of the watch?

Mia has a wallet. It has a mass of Mia has a wallet. It has a mass of 15g and a volume of 5cm15g and a volume of 5cm33. What is . What is the density of the wallet?the density of the wallet?

Which one is more Which one is more dense?dense?

Demonstration: People in a squareDemonstration: People in a square

How about this: Which square is How about this: Which square is more dense?more dense?

Which one is more Which one is more dense?dense?

Now which one is more dense?Now which one is more dense?

By Comparing Densities, By Comparing Densities, you can predict whether an you can predict whether an object will float or sink in a object will float or sink in a

fluid.fluid.

Liquid LayersLiquid Layers

If you pour together liquids that If you pour together liquids that don’t mix and have different don’t mix and have different densities, they will form liquid densities, they will form liquid layers.layers.

The liquid with the The liquid with the highest density highest density will will be on the bottom.be on the bottom.

The liquid with the The liquid with the lowest density lowest density will be will be on the top. on the top.

Liquid LayersLiquid Layers Check out this picture from Check out this picture from

your book. Which layer has your book. Which layer has the highest density?the highest density?

Which layer has the lowest Which layer has the lowest density?density?

Imagine that the liquids Imagine that the liquids have the following densities: have the following densities: 10g/cm10g/cm33.. 3g/cm3g/cm33.. 6g/cm6g/cm33.. 5g/cm5g/cm33..

Which number would go Which number would go with which layer?with which layer?

Liquid Layers – Try with your Liquid Layers – Try with your neighborneighbor

Which liquid has Which liquid has the highest the highest density?density?

Which liquid has Which liquid has the lowest density?the lowest density?

Which liquid has Which liquid has the middle the middle density?density?

Liquid Layers – Try on Liquid Layers – Try on your own!your own!

Imagine that the Imagine that the liquids on the right liquids on the right have the following have the following densities:densities: 15g/cm15g/cm33 10g/cm 10g/cm33

3g/cm3g/cm33 9g/cm 9g/cm33

7g/cm7g/cm33 12g/cm 12g/cm33

Match the colors to Match the colors to the correct the correct densities.densities.

3g/cm3

7g/cm3

9g/cm3

10g/cm3

12g/cm3

15g/cm3

How do Submarines Float How do Submarines Float and then Sink?and then Sink?

Buoyancy & Archimedes Buoyancy & Archimedes PrinciplePrinciple

An An upward forceupward force acting on a acting on a submerged object… opposite to the submerged object… opposite to the direction of gravity.direction of gravity.

If weight of object is > than the buoyant If weight of object is > than the buoyant force, the object will sink. force, the object will sink.

If weight of object is < than the buoyant If weight of object is < than the buoyant force, the object will float.force, the object will float.

Archimedes PrincipleArchimedes Principle = = The Buoyant The Buoyant force acting on a submerged object is force acting on a submerged object is equal to the weight of the fluid equal to the weight of the fluid displaced by the object.displaced by the object.

The pressure on the bottom of a submerged object is greater than the pressure on the top.

The result is a net force in the upward direction.

The block of wood weighs The block of wood weighs less that the weight of the less that the weight of the

water displaced.water displaced.So if floatsSo if floats

The Oak block sinks…we The Oak block sinks…we know that the weight of the know that the weight of the

wood is greater than the wood is greater than the weight of the water weight of the water

displaceddisplaced

A balloon filled with air is A balloon filled with air is more dense than more dense than

surrounding air b/c under surrounding air b/c under pressure. In hot air pressure. In hot air

balloon, air is heated…balloon, air is heated…making it less dense and making it less dense and

therefore it floats.therefore it floats.

ReviewReview

What is the formula for density?What is the formula for density? What happens if you pour together What happens if you pour together

liquids that have different densities?liquids that have different densities? Will the liquid on the top have the Will the liquid on the top have the

highest or lowest density?highest or lowest density? Will the liquid on the bottom have Will the liquid on the bottom have

the highest or lowest density?the highest or lowest density?

Super Scientist Question Super Scientist Question of the Dayof the Day

Jake has a book, a ruler, and a Jake has a book, a ruler, and a balance. balance.

How can Jake find the density of How can Jake find the density of the book with the tools he has?the book with the tools he has?