Earth to Class

Key ideas -- Observations and Measurements

Observations are made with the senses (seeing, hearing, tasting, touching, smelling). For example, "This book is red."

Inferences are conclusions based on one's observations. For example, "The book is old."

Using instruments for measurement extends the senses and makes observations more precise. Instruments may include a centimeter ruler, a triple beam balance, an electronic balance, etc. For example, "The book is 39 cm long" is more precise than saying that "The book is large."

Classification is organizing observations in a meaningful way. For example, "The book is science fiction."

Density is an important property of matter.

Density is defined as mass / volume, and may be expressed in units such as g/cm3 or g/mL.

The same substance always has the same density no matter how big or small the size of the piece, under the same conditions of temperature and pressure.

When pressure increases, its density increases. (For example, this is why you can ride a bicycle on tires filled with air, which is gaseous and low-density.

When the temperature of a gas increases, the density decreases. This explains why a hot air balloon can rise into the atmosphere.

For most substances, as the temperature increases, it expands and the density decreases, and as temperature decreases, it contracts and density increases. This means that a solid sample has the greatest density, a gaseous sample has the leas, and a liquid sample would be in the middle.

Water, an exception to this rule, expands when it freezes. The density of solid ice is less than the density of liquid water. That is why ice floats in water.

Water achieves its greatest density at 4 degrees Celsius in the liquid phase.

Energy flow occurs an interface (boundary between regions with different properties).

The flow is usually from an energy source (object with greater energy) toward the heat sink (object with less energy). This is why your hand will feel a hot metal surface.

Most changes in the environment are cyclical. (lunar phases, seasons, movement of stars and planets, sunspot cycles)

Other changes in the environment are noncyclical, such as volcanic eruptions and earthquakes.

Dynamic equilibrium occurs when a system is in equilibrium (balance) because of constant changes. For example, if one holds a cup under running water, the cup is constantly "full" because an equal amount of water is entering and leaving the cup at the same time. Another example is water behind a dam. Water constantly flows in and out, but the water level behind the dam stays the same.

Pollutants are harmful solids, liquids, gases, biologic organisms, or forms of energy such as heat, sound, and nuclear radiation. Anything that can harm humans or other living things in the environment may be a pollutant. Some forms of pollution are nat

Very large numbers and very small numbers may be expressed more conveniently using powers of ten. For example, 10³ = 1000

Percent deviation or percent error is the difference between the measured and accepted values divided by the accepted value X 100. It tells how far one's answer is from the accepted answer. For example, if the table's measured length is 12.0 cm and the table' actual length is 10.0 cm, the percent error is 2/10 X 100 = 20.0%

Data may be graphed in a variety of ways, such as line graphs, bar graphs, and pie chart.

Data that are graphed may show several different relationships between the x-axis and y-axis components of the data, such as a "direct" relationship, (x increases as y increases; x decreases as y decreases,) an inverse relationship (x increases as y decreases; x decreases as y increases,) x is unaffected by y (as y changes, x remains the same,) and y is unaffected by x (as x changes, y remains the same.)