Chapter 3.2

Chapter 3

Scientific Measurement

Chapter Three: Table of Contents

3.1 Using and Expressing Measurements

3.2 Units of Measurement

3.3 Solving Conversion Problems

Section 3.2

Units of Measurement

What makes metric units easy to use?

All metric units are based on multiples of 10. As a result, you can convert between units easily. 

SI Units

• The International System of Units (abbreviated SI) is a revised version of the metric system. 

• There are seven SI base units, from which all other SI units of measurement can be derived.

• Derived units are used for measurements such as volume, density, and pressure.

Base Units

Commonly Used Metric Prefixes

Metric Units of Length

Metric Units of Volume

Metric Units of Mass

Units of Energy

The SI unit of energy is the joule (J). A common non-SI unit of energy is the calorie. One calorie (cal) is the quantity of heat that raises the temperature of 1 g of pure water by 1°C.

The capacity to do work or to produce heat is called energy. Like any other quantity, energy can be measured.

Temperature

Temperature

• A measure of how hot or cold an object is. 

• Scientists commonly use two equivalent units of temperature, the degree Celsius and the kelvin.

• A change of one degree on the Celsius scale is equivalent to one kelvin on the Kelvin scale. 

• The zero point on the Kelvin scale, 0 K, or absolute zero, is equal to −273.15°C.

Equations to solve for Celsius or Kelvin:

K = °C + 273

°C = K − 273

Example

Normal human body temperature is 37°C. What is this temperature in kelvins?

1 Analyze 

List the known and the unknown. Use the known value and the equation K = °C + 273 to calculate the temperature in kelvins.

KNOWNS

Temperature in °C = 37°C



UNKNOWN

Temperature in K = ? K

2 Calculate: Solve for the unknown

Substitute the known value for the Celsius temperature into the equation and solve.

K = °C + 273 = 37 + 273 = 310 K

3 Evaluate Does the result make sense? 

You should expect a temperature in this range, since the freezing point of water is 273 K and the boiling point of water is 373 K; normal body temperature is between these two values.

Density

• The ratio of the mass of an object to its volume.

• Density is an intensive property that depends only on the composition of a substance, not on the size of the sample.

•  $Density=\frac{Mass}{Volume}$  

Multiple Choice

Which is an example of a base unit?

• g

• mg

• mL

• cm

Multiple Choice

Which prefix represents the numerical value, million?

• k

• G

• m

• M

Multiple Choice

Which of these means 1000 meters?

• 1 millimeter

• 1 kilometer

• 1 centimeter

• 1 decimeter

Multiple Choice

Which of the following units represents a measurement of volume?

• $\frac{g}{mL}$

• g

• mL

• cm

Multiple Choice

What is the base unit for mass?

• kg

• g

• mL

• m

Multiple Choice

Liquid nitrogen boils at 77.2 K. What is this temperature in degrees Celsius?

• -196 °C

• 196 °C

• 350 °C

• -350 °C

Multiple Choice

A 10.0-cm³ piece of lead, for example, has a mass of 114 g. Calculate the density of lead.

• $11.3\ \frac{g}{cm^3}$

• 11.3 g

• -11.3 g

• $-11.3\ \frac{g}{cm^3}$