advertisement

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

• 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