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Topic 1
Earth Science Introductory Unit
è Observations and Inferences
An observation is the use of any of your five senses (touching, tasting, seeing, hearing, smelling) to find out something about your environment (your environment could be your house, bedroom, classroom, etc.).
Because our senses are limited, we sometimes use instruments to help us make better observations.
EX/
Using a ruler to determine the exact length of a table
Using a microscope to see cells
Using a hearing aid to distinguish between bird songs
Sometimes it is necessary to organize our observations in a more meaningful way. This is called classification. Things are classified based on similarities among properties of objects.
Once a lot of observations have been made, you can draw conclusions from them. This is called an inference. [Think of it this way: observations are generally facts; inferences are generally guesses.]
Practice
Determine which of the following statements are observations and which are inferences:
1. The boy’s hair is black. (O)
2. The boy’s hair has not been washed for three days. (I)
3. The boy measures 4 feet, 7 inches tall. (O)
4. The boy’s room smells like a gym locker. (O)
5. The boy likes sports. (I)
è Measurement
Every measurement consists of a numerical quantity and a unit.
Mass: the amount of matter in an object, measured in grams
Volume: the amount of space an object takes up, measured in milliliters or cubic centimeters
Weight: the gravitational pull on an object, varies with distance from the center of the Earth, measured
in Newtons
Density: the amount of matter in a given amount of space (mass divided by volume), measured in g/mL or
g/cm3
Measuring allows us to make detailed, accurate observations. In science, we always measure using the metric system.
Metric prefixes:
Kilo = 1000.
*Hecto = 100. *these prefixes are
*Deka = 10. rarely used
(standard) = 1.
*Deci = 0.1
Centi = 0.01
Milli = 0.001
To convert measurements within the metric system, you can either set up a mathematical proportion and cross multiply, or use the “metric number line.”
kg gram cg mg
km meter cm mm
kL liter cL mL
Rule: Always go from what you know to what you don’t know, and count spaces (not lines!). Move the decimal that many places in that direction.
EX/ How many grams are in 47 kilograms?
To go from kilograms (what you know) to grams (what you don’t know), you move 3 spaces to the left. In the number “47” the decimal is at the end, so move it 3 spaces to the left. Fill in empty spaces with zeroes. The answer is 0.047 grams. (the zero in front of the decimal doesn’t matter)
Practice:
1) How many liters are in 2.96 milliliters? (0.00296 L)
2) 44 meters is equal to how many centimeters? (4400 cm)
3) If you walked 65,028.0 millimeters, how many kilometers would that be? (0.065028 km)
Every measurement contains some error, not always on the part of the person doing the measuring. Sometimes, the equipment is poor. The amount of error in a measurement can be determined by using the following formula, found on your ESRT.
Difference between measured & accepted values
% error = ------Ñ 100
(% deviation) accepted value
è Density
Density is a measure of how much matter is concentrated into a given amount of space, or “mass per unit volume.”
Mass (g)
Density = ------
Volume (cm3)
- The density of a particular substance is always the same, unaffected by size or shape.
- Each pure substance has its own density; therefore, density is a characteristic that helps to identify a substance.
- The density of a particular substance can be changed only by changing its temperature or pressure.
A temperature increase means an increase in volume (because heat makes molecules move faster and spread out)
Increase temperature, decrease density (£ T, ¤ D)
Decrease temperature, increase density (¤ T, £ D)
[an inverse relationship]
An increase in pressure means a decrease in volume (because molecules are getting pushed closer together)
Increase pressure, increase density (£ P, £ D)
Decrease pressure, decrease density (¤ P, ¤ D)
[a direct relationship]
- Temperature and pressure affect gases to a large degree; solids and liquids are only slightly affected
- The maximum density of most substances occurs in the solid phase (state)
- Water is the exception: it’s the only natural substance found in all 3 phases on the Earth and has its maximum density as a liquid at 4°C.
è Graphing
Direct relationship: As one variable goes up, the other goes up also. And, as one variable goes down, the other goes down also. [On a line graph, the line goes up from left to right.]
EX/ Amount of practice shooting hoops and points scored in a game generally have a direct relationship: the more you practice, the more points you should have.
Inverse relationship: As one variable goes up, the other goes down. [On a line graph, the line goes down from left to right.]
EX/ Amount of drugs you do and the number of brain cells you have. The more drugs you do, the fewer brain cells you have.
Constant relationship: As one variable changes, the other is unaffected. [On a line graph, this is either a straight horizontal or vertical line.]
EX/ Time and location of classroom desks. As the days go on, the desks in the classroom stay in the same place. There is no relationship between the two variables.
A state of dynamic equilibrium exists when changes are occurring but there is a balance among the changes so that overall conditions remain the same within the system.
EX/ Water is flowing into a lake at one end and out of the lake at the other end so that the overall water level and conditions within the lake remain basically the same.
Quite often, it is useful to put the data in the form of a graph so it can be understood better.
[Hint: It is extremely rare to use bar graphs or pie graphs in science. It will almost always be a line graph.]
Rules for Making Graphs
1. Pencil only!
2. Use a straight-edge to draw each axis.
3. The independent variable goes on the horizontal (X) axis. The dependent variable goes on the vertical
(Y) axis.
4. You must label the units on each axis! This tells the reader what the numbers represent. [If your
horizontal axis is labeled “TIME,” you must put the unit in parentheses (hours, days, years, etc.)]
5. Lines must be smooth and solid and should not be thicker than the points they’re connecting.
[Although a “best-fit” line is acceptable, we prefer a point-to-point line.]
6. Use an appropriate scale for each axis -- every space along that axis is worth the same amount.
If your data includes a zero, it MUST be at the origin of your graph (unless you also have
negative numbers)
Use a scrunch sign only if you must and use it only at the origin and if you don’t have a zero in
your data
7. All data must fit on the graph scale. If it doesn’t fit, choose a more appropriate scale.
8. The graph should make the best use of all available space (it should not be crammed into a quarter of
the piece of paper).
9. A key must be provided if there is more than one independent variable.
10. The title must include both variables.