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?

What will sink or float in water?
• Penny 1.3 g/ml
• Egg 0.9 g/ml
• Pencil 1.6 g/ml
• Iron 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