8th Grade
Science 100 Facts
The Nature of Science
1.
Technology is the application of science to make products or
tools that people can use.
2.
An observation
is information gathered by using one of our five senses.
3.
An inference
is a logical conclusion based on observations and experience.
4.
Variables are parts of an experiment that can change.
5.
The independent
variable is the factor in the experiment that is manipulated (changed)
and is plotted on the x-axis.
6.
The dependent
variable is the factor in the experiment that is being measured and
is plotted on the y-axis.
7.
Constants are variables that stay the same, so that they do
not interfere with the experiment.
8.
A control
is a sample that is treated like the other experimental groups except that the
independent variable is not applied to it.
Chemistry of Matter
9.
Atoms are the basic building block of all matter.
10.
The nucleus
of the atom contains protons and neutrons.
11.
Protons have a positive charge; neutrons are electrically
neutral or without a charge.
12.
Electrons have a negative charge and are outside the nucleus.
13.
Most of the
atom is empty space occupied by nearly massless
electrons.
14.
The electron
cloud model explains the unpredictable wave behavior of electrons, which
could be anywhere in the area surrounding the nucleus.
15.
Atomic
number is the number of protons in
the nucleus of an atom.
16.
Mass number is the number of protons plus the number of neutrons.
17.
A stable atom
has an equal number of protons and electrons.
18.
Isotopes of an atom have the same number of protons but
different numbers of neutrons.
19.
An ion
is a charged atom with an unequal number of protons and electrons.
20.
The strong
nuclear force holds protons and neutrons together in the nucleus.
21.
A chemical
bond is a force that holds two or more atoms together.
22.
Ionic bonds form when positive and negative ions attract
each other and gain or loose electrons.
23.
Metallic bonds occur when metal atoms share their pooled
electrons.
24.
Covalent bonding occurs when nonmetals share electrons.
25.
The neutral
particle formed when atoms share electrons is called a molecule.
26.
Matter can
change physically or chemically; a process that produces a chemical change is a
chemical reaction.
27.
Physical changes in a substance affect only physical
properties, such as its size, shape, or state.
28.
All matter
has mass and volume (the space matter occupies).
29.
Density is the mass of a substance divided by the volume of
a substance
(d=m/v = g/mL). Water has
a density of 1.0 g/mL.
30.
The law of
conservation of mass states that the mass of the reactants must equal
the mass of the products.
31.
When reactions release
energy (exothermic reactions = increased temperature), the products have bonds
with less energy than those of the reactants.
32.
When reactions absorb
energy (endothermic reactions= decreased temperature), the reactants are more
stable and their bonds have less energy than those of the products.
Ecology
33.
The cell
is the smallest functional unit in an organism.
34.
Organic compounds contain carbon and make up living things
(carbohydrates, lipids, nucleic acids, proteins).
35.
Inorganic substances come from non-living things (e.g.:minerals and water)
36.
Digestion is the breakdown of foods into molecules that cells
can use.
37.
Cellular respiration is a series of chemical processes in which oxygen
combines with food molecules and energy is released; carbon dioxide and water
are waste products.
38.
Photosynthesis occurs in plants and other organisms which contain
chlorophyll; using the energy of sunlight, chlorophyll converts water and
carbon dioxide into sugar (glucose) and oxygen.
39.
Evaporation occurs when a substance changes from a liquid into
a gas; condensation occurs when a substance changes from a gas into a liquid.
Energy and Work
40.
The amount of work
applied to an object is equal to the force multiplied by the distance the
object moved in the direction of the force and is measured in joules (J).
41.
Power is the rate of work or energy is transfer. It is
determined by dividing the work by the time and is measured in watts or
kilowatts. P = W/t = J/s = watts
42.
The five main
forms of energy are: mechanical, heat, chemical, radiant (EM), and
nuclear.
43.
The energy of
motion is called kinetic energy.
44.
The energy of
position is potential energy.
45.
Temperature is a measurement of the average value of the
kinetic energy of the molecules in random motion.
46.
All molecular
motion is theorized to stop at absolute zero (0 K, -273°C).
47.
Heat always moves from warmer objects to cooler objects
until they reach equilibrium.
48.
Conduction is the transfer of heat by direct contact of the
molecules.
49.
Convection is the transfer of heat by molecule movement due to
density changes.
50.
Radiation is the transfer of heat by electromagnetic waves;
which can travel through a vacuum.
Motion and Forces
51.
A force
is a push or pull and is measured in Newtons (N).
52.
Friction is a force that acts to resist movement.
53.
Net force is the sum of all the forces acting on a
mass.
54.
A net force
applied to a mass results in acceleration.
55.
Position (x) is the location of an object at any given time.
56.
Motion is the act of changing position.
57.
Distance (d) is how far an object travels from an initial (xi)
to a final position (xf).
58.
The Greek
letter delta (Δ) represents change.
59.
Speed (v) is the distance an object travels in a unit of
time. (v = d/Δt)
60.
The steeper
the slope of the line on a distance-time graph; the greater the speed.
61.
Velocity is the speed of an object and its direction of
motion. (e.g.: 10 mi/h, east)
62.
Acceleration is change in velocity per unit of time.
63.
The amount of
matter in an object is its mass; inertia is the tendency of an object to
resist a change in its motion.
64.
Momentum is calculated by multiplying mass times velocity.
65.
66.
67.
Newton’s third
law states that forces always act in equal but opposite pairs; for every action
there is an equal and opposite reaction.
68.
Gravity is the attractive force between two objects and depends
on mass and distance.
69.
Mass is constant, but weight changes depending on the gravitational
force.
Earth’s Changes Over
Time
70.
Earth’s crust
and upper mantle are broken into sections.
71.
The sections,
called plates, move on a plastic-like layer of the mantle.
72.
Convection currents in Earth’s mantle are thought to be the
force behind plate tectonics.
73.
Most volcanoes
and earthquakes occur where plates are colliding or moving apart.
74.
Divergent plate boundaries occur where plates move apart.
75.
Most sedimentary
rocks are formed when sediments are deposited, compacted, and cemented.
76.
Igneous rocks are formed when magma cools.
77.
Metamorphic rock is formed when igneous or sedimentary rock is
transformed by heat and pressure.
78.
Transformations
that change one type of rock into another are known as the rock cycle.
79.
The major
causes of erosion are water, ice, plants, wind, and gravity.
80.
Soils are composed of minerals, microorganisms, and
decayed organic matter.
81.
According to
the principle of superposition, in undisturbed layers of rock, the oldest
rocks are on the bottom.
Sound, Light, and Electricity
82.
Waves carry energy,
not matter.
83.
Electromagnetic
waves (EM) which we can see, known
as visible light, have wavelengths from 700-400 billionths of a meter.
(ROYGBIV)
84.
Two types of
waves are transverse (EM) and compression (sound).
85.
Light travels 300,000
km/s or 186,000 mi/s. The distance
light travels in a year would be about 9.5 trillion km (1012) or 5.9
trillion miles away.
86.
At room
temperature, sound travels through air at 340 m/s (1,130 ft/s).
87.
Frequency of
waves is measured in Hertz (Hz).
88.
Electric
current is the flow of charge
through a conductor, measured in amperes.
89.
Like charges
repel, unlike charges attract.
90.
Voltage is a measure of how much electric energy an
electron in a circuit can gain from a battery.
91.
A circuit
is a closed conducting loop through which electric currents continuously flow.
Earth’s Place in the
Universe
92.
The distance
from the Earth to the Sun changes during the year due to the elliptical
orbit.
93.
The impact
theory of the Moon origin states that it was formed 4.6 billion years ago
from Earth material thrown off when a large object collided with Earth.
94.
Earth is the third
planet from the Sun and has over 70% of the surface covered with water.
95.
Earth’s atmosphere
protects us from most meteors and some of the Sun’s radiation.
96.
Scientist
hypothesize that the movement of material inside Earth’s core, along with its
rotation, generate a magnetic field similar to a bar magnet.
97.
Earth’s magnetic
axis moves over time and is currently about 11.5° from the rotational axis.
98.
The Sun is an average,
middle-aged star. Light from the Sun
reaches Earth in about 8 minutes.
99.
Nuclear fusion
occurs in the core of stars where temperatures may exceed 15,000,000 K. During fusion, hydrogen atoms collide with
enough force to make helium and release large amounts of energy.
100.
The Milky Way Galaxy
is usually classified as a spiral galaxy, containing one trillion stars,
and about 100,000 light-years wide.