7.3 Mass and Temperature 429 Mass in the Metric System Weight and mass are not the same. Mass is a measure of the amount of matter in an object. It is determined by the molecular structure of the object, and it will not change from place to place. Weight is a measure of the gravitational pull on an object. The weight of an object varies depending on its location in space. But the mass of the object remains the same regardless of its location. For example, the weight of a rock is less on the moon that it is on the Earth, but the rock has the same mass everywhere. Because the mass of an object does not vary with location, scientists generally use mass rather than weight. Although weight and mass are not the same, on Earth they are proportional to each other (the greater the weight, the greater the mass). Therefore, for our purposes, we can treat weight and mass as the same. The kilogram is the base unit of mass in the metric system. It is about 2.2 pounds. Items that we normally measure in pounds are usually measured in kilograms in other parts of the world. The gram (a unit that is 0.001 kg) is relatively small and is used for items normally measured in ounces. A paper clip has a mass of about 1 g, a cube of sugar has a mass of about 2 g, and a nickel has a mass of about 5 g. It is January, and you visit Niagara Falls, Canada. The thermostat in your hotel room is set on 20 Celsius. ° Will you need to adjust the thermostat? If the temperature outside is ° 15 C, how should you dress? While watching television, you see an astronaut floating while working on the International Space Station. Does this floating astronaut have any weight? Does the astronaut have any mass? In this section, we will discuss these two important metric measurements: temperature and mass. Mass and Temperature SECTION 7.3 LEARNING GOALS Upon completion of this section, you will be able to: 7 Understand mass in the metric system. 7 Understand temperature in the metric system. 7 Convert temperature from Celsius to Fahrenheit or from Fahrenheit to Celsius. Why This Is Important Temperatures in most countries outside the United States are given in degrees Celsius. When temperature is involved in science, it most often is measured in degrees Celsius. Mass is an important concept to all of the sciences. Identify a Suitable Metric Mass Unit 100. Jupiter The planet Jupiter is composed of gas that is in the shape of a sphere. The diameter of Jupiter is 143,000 km. The formula for the volume, v, of a sphere is π = V r , 4 3 3 where r is the radius of the sphere. Determine the volume of the gas that makes up Jupiter. Write your answer using scientific notation (see Section 5.6). 1.5310 km 15 3 ≈ × 101. Square Mile In Example 3, we illustrated how to change an area in a metric unit to an area measured with a different metric unit. Convert 1 square mile to square inches. 4,014,489,600 sq in. 102. Cubic Miles Convert one cubic mile to cubic inches. See Exercise 101 and Example 3. Write your answer using scientific notation. 2.5410 in 14 3 ≈ × Research Activity 103. The Meter and the Liter Write a report on the history and the use of the meter and the liter. Include various definitions that have been used throughout history. Photomanz/ Shutterstock
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