Density Notes - Jamestown School District

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DENSITY

Goal: To measure density using the proper units and equipment

What is density?

• Density is:

The number of particles packed into a space

• Formula:

Density = Mass/Volume

How do you calculate density?

1. Mass of object (grams)

2. Volume of object (ml or cm 3 )

3. Mass divided by volume

4. Round to nearest tenth

5. Label answer (g/ml or g/cm 3 )

Density Example

• Density = Mass/Volume

• Example 1:

–The mass of a block is 100 g.

The volume of the block is 5 cm 3 . What is the block’s density?

ANSWER:

• M= 100g

• V= 5 cm 3

• D = m/v

• D= 100g / 5 cm 3

• D= 20.0 g/cm

3

Example 2

• The mass of a rock is 20.5 g. The volume of the rock is 41.0 ml. What is the rock’s density?

• M= 20.5 g

• V= 41.0 ml

• D= m/v = 20.5 g / 41.0 ml

• D= 0.5 g/ml

DENSITY

• When you find the density of an object, the number you calculate tells you whether the object will sink or float when placed in water.

• Density of water= 1 g/ml

• Less dense items float in water

• More dense items sink in water

So……………

• Density > 1 g/ml, the object will sink

• Density < 1 g/ml, the object will float

• Here’s an example

• A toy car with a mass of 20 g and a volume of 10 ml would have a density of what?

• Density = 20/10 = 2 g/ml

• Would this sink or float in water?????????

• SINK- Why?

• It’s density is greater than 1 g/ml.

Example

• A bar of soap has a mass of 15 g and a volume of 45 cm^3. Will it sink or float when placed in water?

• FLOAT- Why?

• It has a density of .3 g/cm^3, which is less than 1, the density of water

Which objects will sink or float?

HOLD UP SINK IF THE

OBJECT WILL SINK,

HOLD UP FLOAT IF THE

OBJECT WILL FLOAT

What will sink or float in water?

• Penny 1.3 g/ml

• Egg 0.9 g/ml

• Pencil

• Iron

1.6 g/ml

4.8 g/ml

• Pumice 0.7 g/ml

• Silver 3.2 gml

• Rock 1.1 g/ml

Density of liquids

• What will liquids with different densities do when poured into the same jar?

• They will layer according to density

• Liquids with higher densities will go to the bottom, liquids with lower densities will float to the top

• Look at the example on the front counter

Example on counter

• The jar contains the following:

• Which layer is which then?

– Water = 1 g/ml

– Oil = 0.7 g/ml

– Syrup = 3.2 g/ml

– Liq. Soap = 2.5 g/ ml

• Draw a picture in your notes and label it with the correct name of each liquid

Which is which?

• Top = Oil

• 2nd = Water

• 3rd = Soap

• Bottom = Syrup

Example

• Please draw a picture of how the following liquids would layer out in a jar:

• Mercury = 5.6 g/ml

• Italian dressing = 0.7 g/ml

• Water = 1 g/ml

• Antifreeze = 1.4 g/ml

• Paint thinner = 0.3 g/ml

Answer:

Top= PAINT THINNER

• ITALIAN DRESSING

• WATER

• ANTIFREEZE

Bottom =MERCURY

Is there a way to estimate density?

• You can estimate density by putting the object in water

• If it sinks d > 1 g/ml

• If it floats d < 1 g/ml- see how much of the object is below the water

• Remember: Density corresponds to the amount of the object below the water’s surface !

• Look at the block on the front counter.

What is it’s approximate density???

• What would happen to the density of this block if I were to cut in in half?

• How about if I cut it into six pieces?

• NOTHING WOULD HAPPEN TO ITS

DENSITY!!

• Density of an object remains the same even when the object is cut into smaller pieces

• An object’s density always remains the same !!!!

• The density of copper is always 8.9 g/mlno matter how big or small!

• The density of Nylon is always 1.13 g/mlno matter how big or small !

• Density can help identify what a material is made of !!!

Last Example

• A cube has a mass of 14.3 g and a volume of 5.3 ml. What is the cube made of?

• A. Copper 8.9 g/ml

• B. Acrylic 1.17 g/ml

• C. Oak 0.7 g/ml

• D. Aluminum 2.7 g/ml

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