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Measuring Density

Background

All matter has mass and volume. Mass is a measure of the amount of matter an object has. Its measure is usually given in grams (g) or kilograms (kg). Volume is the amount of space an object occupies. There are numerous units for volume including liters (l), meters cubed (m3), and gallons (gal).

Mass and volume are physical properties of matter and may vary with different objects. For example, it is possible for two pieces of metal to be made out of the same material yet for one piece to be bigger than the other. If the first piece of metal is twice as large as the second, then you would expect that this piece is also twice as heavy (or have twice the mass) as the first. If both pieces of metal are made of the same material the ratio of the mass and volume will be the same.

We define density () as the ratio of the mass of an object to the volume it occupies. The equation is given by:

(1.1)

here the symbol M stands for the mass of the object, and V the volume. Density has the units of mass divided by volume such as grams per centimeters cube (g/cm3) or kilograms per liter (kg/l).

Sample Problem #1

A block of wood has a mass of 8 g and occupies a volume of 10 cm3. What is its density?

Solution

The density will be

.

This means that every centimeter cube of this wood will have a mass of 0.8 grams.

Activity 1: (Determine the density of an object with a regular shape.)

Obtain a set of objects (cube, cylinder, sphere, etc.) made of the same material. Calculate the density by measuring the mass and volume of your samples.

Measuring the Mass

Measure the mass of your samples using the triple beam balance provided. You will make this measurement three times and calculate the average. Record your results in the table below.

Trial

Sample 1

Sample 2

1

2

3

Avg.

Measuring the Volume

To determine the volume of an object with a regular shape there are standard equations that may be used. The equations for three common shapes are given below.

Sphere

Cube

Cylinder

(1.2)

Measure the relevant dimensions of your sample and record the reading in the tables below.

Sample #1

Trial

Length (cm)

Width (cm)

Height (cm)

1

2

3

Avg.

Calculate the volume of Sample #1 using equations (1.2). Show all work

Volume = ____________________________________________________.

Sample #2

Trial

1

2

3

Avg.

Calculate the volume for Sample #2. Show all work

Volume = ____________________________________________________.

Calculate the Density

Specimen

Volume

(cm3)

Mass

(grams)

Density

(gm/cm3)

Even though both object have different shape and volume what did you observe about the density of the samples: ___________________________________________________________

Unlike the mass...

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