1. Measurements and Calculations
Chapter 2
Measurements and Calculations
p29

2. HRW 2.1 Scientific Method
Describe the purpose of the scientific method.
Distinguish between qualitative and quantitative observations.
Differentiate hypotheses, theories, and models.
HRW 29 Section 2-1

3. Types of measurement Quantitative - use numbers to describe
Qualitative - use description without numbers
Which are the following?
4 feet
extra large
Hot
100º C
System: specific portion of matter in given region of space selected for study
HRW 29 Section 2-1 Observing & Collecting Data

4. Scientists prefer Quantitative - easy to check
Easy to agree upon, no personal bias
The measuring instrument limits how good the measurement is.

5. Scientific Method A way of solving problems or answering questions.
Starts with observation - noting and recording facts.
Not necessarily stepwise. May repeat steps.
HRW 29 Section 2.1

6. Scientific Method
Model - Explanation of how phenomena occur. Not real.
Theory - Broad generalization that explains a body of facts or phenomena.
Hypothesis- an educated guess as to the cause of the problem or answer to the question.
HRW 29 Section 2.1

7. Scientific Method Experiment- designed to test the hypothesis
Only two possible answers
hypothesis is right, or
hypothesis is wrong
Generates data observations from experiments.
Modify hypothesis - repeat the cycle

8. Observations Hypothesis Experiment Cycle repeats many times.
The hypothesis gets more and more certain.
Becomes a theory
A thoroughly tested model that explains why things behave a certain way.
Observations
Hypothesis
Experiment

9. Theory can never be proven.
Useful because it predicts behavior
Helps us form mental pictures of processes (models)
Observations
Hypothesis
Experiment

10. Another outcome is that certain behavior is repeated many times
Scientific Law is developed
Description of how things behave
Law - how
Theory - why
Observations
Hypothesis
Experiment

11. Law Modify Observations Theory (Model) Hypothesis Experiment
Prediction
Modify
Experiment
Experiment
Law

12. HRW 2.2 Units of Measurement
Distinguish between a quantity, a unit, and a measurement standard.
Name SI units for length, mass, time, volume, and density.
Distinguish between mass and weight.
Perform density calculations.
Transform a statement of equality to a conversion factor.

13. Measuring The numbers are only half of a measurement It is 10 long
10 what.
Numbers without units are meaningless.
Rod = 1.5 feet (furlong = 660 ft; 1 league = 24 furlongs)

14. The Metric System Easier to use because it is a decimal system
Every conversion is by some power of 10.
A metric unit has two parts
A prefix and a base unit.
prefix tells you how many times to divide or multiply by 10.

15. SI Measurement Le système International d’Unités
World’s scientists adopted this in 1960.
Don’t use commas because this means a decimal point in some countries.
Use a “space” instead.
75,000 is written as (with a space)
Otherwise, if you wrote 75,000 a German scientist would think you meant
Hrw 33

16. The 7 Base SI Units - (Table 2-1 p. 34 )
Length - meter (more than a yard) - m
Mass - grams (about a raisin) - kg
Time - second - s
Temperature - Kelvin (ºCelsius) K or (ºC)
Energy - Joules- J
Volume - Liter - half a two-liter bottle - L
Amount of substance - mole - mol
Kilogram = base unit, but we will use grams

17. Prefixes (Table 2-2 p. 35, Tr 4A)
kilo k 1000 times
deci d 1/10
centi c 1/100
milli m 1/1000
kilometer - about 0.6 miles
centimeter - less than half an inch
millimeter - the width of a paper clip wire

18. Learning Check Indicate the prefix to use for
1. A mass that is 1000 times greater than 1 gram
1) kilo 2) milli 3) mega
2. A length that is 1/100 of 1 meter?
1) deci 2) centi 3) milli
3. A unit of time that is 1/1000 of a second.
1) nanosecond 2) microsecond 3)millisecond
kilo
centi
millisecond

19. Mass Weight is a force (pull of gravity)
Mass is the amount of matter - the resistance to a change in motion.
1 gram is defined as the mass of 1 cm3 of water at 4 ºC.
1000 g = 1000 cm3 of water
1 kg = 1 L of water
Hrw 34

20. Mass 1 kg = 2.2 lbs 1 g = 1 paper clip
1 mg = 10 grains of salt or 2 drops of water.

21. Length SI base unit = meter 1 meter = 1 m = about width of a doorway.
1 km = 1000 m = about 0.6 miles
5K race is about 3 miles.
Hrw 35

22. Volume A derived unit (combo of base units)
Calculated by multiplying L x W x H
Liter = volume of a cube 1 dm (10 cm) on a side = 1 dm3
So, 1 L = 10 cm x 10 cm x 10 cm
1 L = 1000 cm3
1/1000 L = 1 cm3
1 mL = 1 cm3 - Know this!
Hrw 37

23. Volume 1 L is about 1/4 of a gallon - a quart
1 mL is about 20 drops of water or 1 sugar cube

24. Density How heavy something is for its size
The ratio of mass to volume for a substance
D = m / v (triangle method)
Independent of how much of it you have
An Intensive physical property
gold - high density
air - low density.
Hrw 38. Triangle method on teacher notes p. 38

25. Calculating The units tell you how to calculate.
units will be g/mL or g/cm3
A piece of wood has a mass of 11.2 g and a volume of 23 mL what is the density? (“triangle” on whiteboard)
A piece of wood has a density of 0.93 g/mL and a volume of 23 mL what is the mass? (“triangle” on whiteboard)
Show “triangle” trick to remember density.
0.49 g/ml (2 sig figs)
21 g

26. Floating Lower density floats on higher density.
This is not the same as weight.
Ice is less dense than water
Most wood is less dense than water
Helium is less dense than air.
A ship is less dense than water.
2 x 250 bkrs, one with 200 ml water, other with 200 ml acetone or alcohol, 2 ice cubes; put ice cube in each; one sinks, one floats.

27. Density of water 1 g of water is 1 mL at 4ºC (exact).
So, density of water is 1 g/mL at 4ºC
Otherwise, it is less.

28. Tr 6A Table 2.4 p. 38 Some Densities
Which liquid is the densest?
Mercury
Which has greater mass: 2 cm3 butter or 2 cm3 ice?
Ice
Does ice float or sink in turpentine?
Sink.
Why isn’t water’s density 1.00 g/mL?
It’s not at 4º C.

29. Learning Check D1 Osmium is a very dense metal. What is its
density in g/cm3 if g of the metal occupies
a volume of 2.22cm3?
1) g/cm3
2) 22.5 g/cm3
3) 111 g/cm3
22.5 g/cm3

30. Learning Check 1) 0.2 g/ cm3 2) 6 g/cm3 3) 252 g/cm3
What is the density (g/cm3) of 48 g of a metal if the metal raises the level of water in a graduated cylinder from 25 mL to 33 mL?
1) 0.2 g/ cm ) 6 g/cm ) g/cm3
33 mL
25 mL
6 g/cm3

31. Conversion factors “A ratio of equivalent measurements.”
Start with two things that are the same.
One meter is one hundred centimeters
Write it as an equation.
1 m = 100 cm
Now write it as a ratio
Hrw 40

32. Write the conversion factors for the following
kilograms to grams. Answer . . .
1 kg/1000 g or 1000 g /1 kg
feet to inches. Answer . . .
12 in/1 ft or 1 ft/12 in
1.096 qt. = 1.00 L Answer . . .
1.096 qt/1.00 L or 1.00 L/1.096 qt

33. What are they good for?
We can multiply by one creatively to change the units .
13 inches is how many yards?
We know that 36 inches = 1 yard.

34. Dimensional Analysis (Whiteboard)
A ruler is 12.0 inches long. How long is it in cm? (1 inch is 2.54 cm)
In meters?
A race is 10.0 km long. How far is this in miles?
1 mile = 1760 yds
1 meter = yds
30.5 cm
0.305 m
1.61 mi
4301 m

35. Multiple units The speed limit is 65 mi/hr. What is this in m/s?
1 mile = 1760 yds
1 meter = yds
29 m/s