Title: Measuring Mass, Calculating Density

Activity 9

Read pg. A-36

Problem: How can you use the mass and volume of an object to calculate its density?

Hypothesis/Initial Thoughts:

What is mass (in science!)?

•Mass is a measure of the number of atoms in an object combined with the density of those atoms. Usually people measure mass in kilograms. You can tell how much mass something has by measuring how hard it is to get that thing to change directions or slow down.

What is the difference between mass and weight?

• Mass is the amount of matter in an object.

• Weight is a measurement of a gravitational force between two objects.

• People often get mass mixed up with weight, because when you're on Earth, the two are pretty much the same - things with more mass also have more weight.

Mass vs. Weight

Mass vs. Weight

• On the Moon, an object weighs less than it does on Earth because the Moon is smaller and has less gravitational pull on the object.

• An object will have the same mass on both the Moon and on Earth because it is taking up the same amount of space.

• Mass is not the same as size - some big things, like balloons, are very light, while some small things, like a lead fishing weight, are very heavy. A truck would be the same size whether it was empty or full, but it would have a lot more mass if it was full - and it would be even harder to stop.

Density

• In Activity 7, you looked at relative density. What does that mean?

• These observations of density are qualitative; they do not include measurements, but only provide comparisons with water or ethanol.

Density• What is Density?

– Density is the mass per volume. – Finding density through measurement is

quantitative

• Your job is to measure the density of each object and see how the objects compare to each other.

How do the densities of the light gray and dark gray materials

compare with each other?

• Density = mass/volume

• Measure the mass and divide it by the volume you calculated in Activity 8.

• UNITS!!!!

• Look at Table 3 on A-40

• Make sure to rotate who is taking the mass.

Balances

• Handle carefully

• Calibrate to Zero

• Be ACCURATE!!!

• Units?

–Grams

Data/Observations:Table 1: Mass, Volume, and Density of Six Objects

Object Mass (g) Volume (cm3 or mL)

Density calc. Density (g/cm3 or g/mL)

Lt. gray bar

Drk. gray bar

Lt. gray cube44.105 g 15.6 cm3 d = 2.8 g/cm3

Drk. Gray cube

15.6 cm3

Lt. gray cylinder

Drk. gray cylinder

From Activity 8

44.105 g

15.6 cm3

Discussion

• Compare your densities to those of other groups.

• Why may they be different?

Does the density of a material change if its size changes?

What do you think will happen to the density of this clay if I

cut it in half?

• If a piece of clay that is 10 g in mass and has a volume of 5 cm3 (density 2 g/cm3) is cut in half, what will be the density of the two new pieces of clay?

Conclusion

• Mass and volume depend on the object.

• Density depends on the material the object is made of.

• Density is independent of the amount of the material

Unit A Major Concept• Physical Properties can be measured

or observed using one or more of your 5 senses.

• Chemical properties of matter describes its "potential" to undergo some chemical change or reaction.

Unit A Major Concept

• Substances have characteristic properties, such as density, that are independent of the amount of the sample.

• Density = Mass/Volume

in g/cm3 or g/mL

• 1 mL = 1 cm3

Unit A Major Concept

• To find the density of a regular object, calculate the volume (length x width x height) and then divide mass (g) by volume (cm3).

• To find the density of an irregular object, find the volume using water displacement and then divide divide mass (g) by volume (mL).

Unit A Major Concept

• If an object is more dense than a liquid, it will sink.

• If an object is less dense than a liquid, it will float.

• This is called relative density

Quiz Next Week!

• The quiz will be on the Unit A Major Concepts (Mastery Quiz) and the Unit A Vocabulary.