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Measuring Mass Using a Digital Scale.
Suppose that you needed to measure 5 grams of flour into a plastic weighing boat.
Using the digital scale provided, write a procedure that begins with unlocking the
balance and turning on the scale. Then explain how to zero the scale, zero the scale
with the empty container, and how you would go about placing 5 grams of flour in a
plastic weighing boat using a scoopula.
Explain cleanup (turn off scale and remove pan to clean it) and relocking the balance.
PROCEDURE:
What is the range of the electronic balance?
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CALCULATIONS AND GRAPHING
When completing labs, you will often be asked to utilize your measurements and make some type of
calculation or create a graph.
Calculations
One common kind of calculation in science and math is determining rates. One definition of rate is the
speed at which something happens. For example, you may need to know how often something occur
per minute, or determine the growth of a plant per day.
Rates are used by ecologists to determine birth and death rates. Rates are utilized by chemists or
biologists to determine how rapidly a reaction occurs. If you know the rate at which something
happens, you can use this information to determine how often something happens in any given time
period. For example, you check your pulse and determine that there are 20 pulses in a 15 second
period. You are now asked to determine your pulse rate per minute. To determine this, you need to
CONVERT the time unit you have into minutes.
Conversion is accomplished by multiplying by a term that is equivalent to 1, but contains both the unit
you start with and the unit you wish to end with. For example: 1 minute = 60 seconds.
20 pulses
15 seconds
We want to replace seconds with minutes. If we multiply this rate by 60 seconds
1 min
You can cross out “seconds” and are left with
1200 pulses
15 min
=
80 pulses
1 min
When asked to do calculations, show work, and each step of the calculation. Be sure you show units
and the conversion factor. Make sure your final answer is labeled with the correct units.
Complete the Skills Practice: Calculations
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Graphing
Graphs are utilized to help interpret data. Graphs are utilized so that patterns in the data can be seen.
Patterns help us to understand how the dependent and independent variable are related.
Data should be placed in a table (or in a spreadsheet) before attempting to draw a graph. It is
important to order the data in the table so that it best addresses the question you are trying to answer.
Example: Suppose that a scientist is measuring the speed that sound waves travel at different air
temperatures. An experiment was performed, and data were gathered on different days . All
temperatures are in oC.
Date
Temperature
Speed of sound (m/s
June 5
10
336
July 19
30
348
Aug 5
20
342
Oct 1
0
330
Oct 10
-10
324
Jan 20
-20
318
What question is the scientist trying to answer?
Which two columns of data are most important in answering the question
Which measure DEPENDS on the OTHER VARIABLE?
Rearrange the data in a new table on the next page, then graph the data and provide an appropriate
title
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Graph Title
Title:
Which variable, X or Y is dependent
variable? (it DEPENDS on the setting of
the other). Which variable is the
INDEPENDENT variable?
Variable on Y axis:______________
Variable on X axis:________________________
Be sure to name the graph AND name the table and label the two axes (with the UNITS)
What number did you choose to start each axis? Why ? What type of graph did you choose? Why?
What can you conclude (or infer) from your graph?
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On Your Own
Number of Frog Croaks at Different
Temperatures
Croaks/Minute
30
25
20
15
10
20
22
24
26
28
30
32
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Temperature C
Write a sentence that summarizes the data.
What is the difference between the greatest number of croaks measured in a minute and the least
number of croaks measured in a minute?
What was the greatest temperature at which information about frog croaks was collected?
What number of croaks would you expect to hear if the temperature were 21 C? Why?
Does the number of frog croaks increase the same amount for each degree of temperature increase?
Write a sentence that describes any trends you note in the data.
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OPERATIONAL DEFINITIONS
In science, exact definitions are important. An exact definition allows scientists to repeat their own
work and the work of others. An operational definition is a statement that describes how a particular
variable is to be measured, or how an object or condition is to be recognized. The word operational
means “to describe what to do”). Operational definitions are used whenever a term doesn’t have a
clear single meaning. In experiments, operational definitions are contained in “Materials and
Procedures”.
OPERATIONAL DEFINITIONS (PROCEDURES) IN EXPERIMENTS
Suppose you are conducting an experiment to determine how air temperature in a room affects the
growth rate of plants. If the lab report said “some of the plants were kept in a cold room, while others
were kept in a warm room”, you would not be able to repeat the conditions of the experiment. The
words cold and warm do not have a single clear meaning. An operational definition should be used in
your lab report. A statement such as “some of the plants were kept in a room with an air temperature
of 10 C and other plants were kept in a room with an air temperature of 30 C”, would have the
information that you needed to repeat the experiment’s conditions.
Operational definitions are also used to describe how variables are measured. In the
experiment described above, we are measuring the growth of a plant over time. So a lab report must
include how the rate of plant growth was determined.
EXAMPLE: The height of the plants was measured once every 24 hours using a centimeter ruler. The
height was measured to the nearest centimeter. The change in height was determined by subtracting
the previous day’s height from the current height. The rate of growth was reported based on change
in centimeters per day.
When you write an operational definition, make sure it describes what to do or what to observe. Be
sure that any terms in your lab report that do not have a single, clear meaning have an operational
definition. Here are some examples of operational definitions.
MORE EXAMPLES:
1. The maple tree population in an area of 100 square meters increased compared to last year.
OPERATIONAL DEFINITION: The maple tree population in an area was determined by counting
the number of maple trees in one tenth of the area and multiplying that number by 10.
2. Cut flowers stay fresh longer if they are kept in room temperature water (70F) than they do if
they are kept in cold water (45F).
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OPERATIONAL DEFINITION: Fresh: cut flowers are considered “fresh” if they were cut within 2
hours of being placed in water and have not lost any petals.
A good operational definition should also tell how frequently a particular measurement is made.
1. If an experiment requires the measurement of the temperature of a beaker of water as it heats
over a flame, the operational definition might be: the temperature of the water is measured in
o C at 5 min intervals, using a thermometer.
SUMMARY: Operational Definitions should be:
1.
2.
3.
4.
5.
Written as you plan your investigation or experiment
Written when a term does not have a single, clear meaning
Used to clarify methods used to measure variables
Used to allow someone to duplicate your work
Be checked by someone to ensure the directions are accurate.
Complete Worksheet: Forming Operational Definitions
For each phrase that is underlined on the next page, define what the phrase means (YOU assign
a definition to the phrase
Example: Look at the first example: smallest one is underlined. Does smallest mean: smallest
diameter or smallest mass? You define it more precisely.
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