Using Measurements in Calculations

Density is an example of a value that is calculated using two measurements. Density represents the amount of mass in a particular volume of a substance. The units used for density are grams per milliliter (g/mL) or grams per cubic centimeter (g/cm3). Density is calculated by dividing an object's mass by its volume.

Example

Follow these steps to calculate the density of an object.

  1. Measure and record the mass of an object in grams.

  2. Measure and record the volume of an object in mL or cm3.

  3. Use the following formula to calculate density:

Density is equal to Mass divided by Volume.

Effects of Measurement Errors

Density is calculated using two measured values. An error in the measurement of either mass or volume will result in the calculation of an incorrect density.

Example

A student measured the mass of an object as 2.5 g and its volume as 2.0 cm3. The actual mass of the object is 3.5 g; the actual volume is 2.0 cm3. What is the effect of the measurement error on the calculation of density?

Follow these steps to determine the effect of a measurement error on calculation.

  1. Determine the density using the student's measurements.

    Density = Mass/Volume

    Density = 2.5 g/2.0 cm3

    Density = 1.25 g/cm3

  2. Determine the density using the actual values.

    Density = Mass/Volume

    Density = 3.5 g/2.0 cm3

    Density = 1.75 g/cm3

  3. Compare the calculated and the actual values.

In this case, a measurement of mass that was less than the actual value resulted in a calculated value for the density that was less than the actual density.

Accuracy

The accuracy of a measurement is its closeness to the actual value. Measurements that are accurate are close to the actual value.

Both clocks on this page show a time of 3:00. Suppose, though, that these clocks had not been changed to reflect daylight savings time. The time shown on the clocks would be inaccurate. On the other hand, if the actual time is 3:00, these clocks would be accurate.

Precision

Precision describes the exactness of a measurement. The clocks shown on this page differ in precision. The analog clock measures time to the nearest minute. The digital clock measures time to the nearest second. Time is measured more precisely by the digital clock than by the analog clock.

A digital and an analog clock shows the time as 3.

Comparing Accuracy and Precision

There is a difference between accuracy and precision. Measurements can be accurate (close to the actual value) but not precise. Measurements can also be precise but not accurate. When making scientific measurements, both accuracy and precision are important. Accurate and precise measurements result from the careful use of high-quality measuring tools.

End ofPage A-20

Table of Contents

Miller & Levine Biology
About the Authors
Changing the World of Biology Education
Contents
Diversity of Life: A Visual Guide DOL•1–DOL•64
Labs and Activities
Features
UNIT 1 The Nature of Life
1 The Science of Biology
2 The Chemistry of Life
Unit Project
UNIT 2 Ecology
3 The Biosphere
4 Ecosystems and Communities
5 Populations
6 Humans in the Biosphere
Unit Project
UNIT 3 Cells
7 Cell Structure and Function
8 Photosynthesis
9 Cellular Respiration and Fermentation
10 Cell Growth and Division
Unit Project
UNIT 4 Genetics
11 Introduction to Genetics
12 DNA
13 RNA and Protein Synthesis
14 Human Heredity
15 Genetic Engineering
Unit Project
UNIT 5 Evolution
16 Darwin's Theory of Evolution
17 Evolution of Populations
18 Classification
19 History of Life
Unit Project
UNIT 6 From Microorganisms to Plants
20 Viruses and Prokaryotes
21 Protists and Fungi
22 Introduction to Plants
23 Plant Structure and Function
24 Plant Reproduction and Response
Unit Project
UNIT 7 Animals
25 Introduction to Animals
26 Animal Evolution and Diversity
27 Animal Systems I
28 Animal Systems II
29 Animal Behavior
Unit Project
UNIT 8 The Human Body
30 Digestive and Excretory Systems
31 Nervous System
32 Skeletal, Muscular, and Integumentary Systems
33 Circulatory and Respiratory Systems
34 Endocrine and Reproductive Systems
35 Immune System and Disease
Unit Project
A Visual Guide to The Diversity of Life
HOW TO USE THIS GUIDE
THE TREE OF LIFE
Bacteria
Protists
Fungi
Plants
Animals
Appendices
Appendix A Science Skills
Appendix B Lab Skills
Appendix C Technology & Design
Appendix D Math Skills
Appendix E Periodic Table
Glossary
A
B
C
D
E
F
G
H
I
J
K
L
M
N
O
P
Q, R
S
T
U
V
W
X, Y, Z
Index
A
B
C
D
E
F
G
H
I
J
K
L
M
N
O
P
Q
R
S
T
U
V
W
X
Y
Z
Credits
Go to previous page Go to next page