8th Grade CST Science
Concept Review
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Created by: Monica Sevilla
Speed
Speed = Distance/Time
Distance = Speed x Time
Time= Speed/Time
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Average Speed
The Average Speed:
Total distance/Total Time
d1 + d2…/t1 + t2
(for distances at different time intervals)
Position of an Object
The position of an object is the reference
point of an object in relation to a set of
reference directions ( I.e. north, south,
east, west,..)
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Velocity
Velocity is the rate of change in the position of
an object.
Velocity specifies both the speed and the
direction of an object. (i.e. 40 m/s north)
Velocity may be due to changes in speed,
direction, or both.
Changes in Velocity
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Changes in Velocity can occur when there is a
change in speed or direction.
Remember, that speed includes distance and
time. Any change in distance or time will
result in a change in the speed.
Acceleration
Acceleration = Speed/Time
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Speed = Acceleration x Time
Time = Speed/Acceleration
Force
Force = Mass x Acceleration
Mass = Force/Acceleration
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Acceleration = Force/Mass
A force has both magnitude and direction.
The greater the mass of the object, the more force is
needed to achieve the same rate of change in
motion.
Forces
There are always 2 or more
forces acting on static or
stationary objects.
Examples of these forces are:
friction, gravity, elastic
forces due to tension or
compression of matter.
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Unbalanced Forces
Unbalanced [pp[forces cause QuickTime™ and a
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When an object has 2 or more
forces acting on it at the
same time, the result is the
cumulative effect of all the
forces.
Force
Force = Pressure x Area
Force/Pressure = Area
Force/area = Pressure
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Gravity
Gravity is an acceleration of an
object towards the center of the
Earth.
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It is calculated at 9.8m/s2
It plays an important role in forming
and maintaining the shapes
(spheres) of planets, stars, and the
solar system (elliptical orbits).
Balanced Forces
If 2 forces (A and B) are equal in
magnitude (balanced) but opposite
directions, the resultant force is 0. This
will not change the motion of the object.
Example:
2N - 2N = 0
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When Forces Balance
Each Other
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Weight of an Object
Weight is a force due to the mass of an object
and the acceleration due to gravity acting
upon it.
= Mass x Speed/Time
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Weight = Mass x 9.8 m/s2
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When the upward force of air resistance becomes
equal to the downward pull of gravity on a falling
object, the two forces are balanced and the object
will slow to a stop.
Resolving Unbalanced Forces
If 2 forces (A and B) acting on an object have
different magnitudes and are in opposite
directions, the resulting force is the difference
between the two forces. The velocity of the
object changes as well.
Example:
20 N North - 15N South = 5 N North
The resulting direction of the force is assigned to
the larger of the two forces. In this case, 20 N
North is the larger of the two forces. Therefore,
the resulting force is assigned the North
direction.
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Weight of an Object
Weight is a force due to the
mass of an object and the
acceleration due to gravity
acting upon it.
Force = Mass x Acceleration
Weight = Mass x 9.8 m/s2
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Physical Properties
Substances can be classified by their physical
properties.
Physical Properties Include:
Density
Melting Temperature
Hardness
Thermal conductivity
Electrical Conductivity
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Physical Properties
Substances can be classified
by their physical
properties.
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Metals are strong thermal
and electrical Conductors.
Chemical Properties
Chemical Properties include:
Reactivity: the ability of a
substance to change into one
or more new substances.
Flammability: the ability of a
substance to burn
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Density
Density = Mass/Volume
Mass = Density x Volume
Volume = Density/mass
Volume
Volume = area x height
Volume = L x W x H
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Density of Water
The density of water is 1.0 g/cm3
An object or substance will float if
its density is lower than water.
An object or substance will sink if
its density is higher than water.
Oil floats on top of water because
its density is lower than water.
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Buoyant Force
The Buoyant Force
on an object in a
fluid is an upward
force equal to the
weight of the fluid
the object has
displaced.
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Structure of Matter
Each of more than the 100 elements of
matter has distinct properties and a
distinct atomic structure.
All forms of matter are composed of one
or more of the elements.
The Atom
The Atom is composed of a
core of protons, neutrons,
surrounded by electrons.
The nucleus of the atom is
composed of protons and
neutrons.
Electrons are are found
farthest from the center of
the atom.
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Compounds
Compounds are formed by combining 2 or
more different elements together.
Compounds have properties that are
different from the individual elements.
Example: H20 water
The Periodic Chart
Be able to identify the elements and symbols
from the periodic chart.
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The Periodic Chart
Periods: Each horizontal row in the chart.
Changes in chemical properties of elements
across the period correspond to changes in
the electron arrangements of the atoms of
the element.
Groups: Each vertical column in the chart.
The elements in the group have a similar
chemical properties because their atoms
have a similar number of electrons in their
outer energy level.
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The Periodic Chart
Be able to find: metals, nonmetals on the chart
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Solids
Atoms and molecules form solids by
buiding up repeating patterns such as
crystal structures or long chain
polymers such as glucose (C6H12O6).
Example of a crystal: NaCl
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States of Matter
The States of Matter (Gases, Liquids, and Solids)
depend on the motion of molecules.
Gases: molecules are free to move independently and
collide frequently.
Liquids: molecules are more closely connected, collide,
and can move past one another.
Solids: molecules are closely locked into position and
vibrate.
States of Matter
Molecular Arrangement and Motion
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States or Phases
for Water (H2O)
Gas: 100 degrees Celcius or more (evaporation occurs)
density is less than 100 g/ml
heat energy is absorbed, bonds are broken
Liquid: 33-99 degrees Celcius
density is 1.0 g/ml
Solid: 32 degrees Celcius or less
(freezing occurs)
forms a cystalline structure that floats on water
density is less than 1.0g/mL
heat energy is released.
The Periodic Chart
The Periodic Chart is organized based
on the properties of the elements and
reflects the structure of the atoms.
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Properties of Metals
Metals are shiny.
They are malleable or easily
pounded or rolled.
They are good conductors of
thermal and electrical
energy.
They are ductile or can be
drawn into thin wires.
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Groups of Elements:
Alkali metals: Li, Na, K, Rb, Cs, Fr
Alkaline metals: Be, Mg, Ca, Sr, Ba, Ra
Transition metals: groups 3-12 I.e. Cr, Mn, Fe, Co, Ni,
Cu, Ag, Au, Hg
Boron Group: B, Al, Ga, In, Tl, Uut
Carbon Group: C, Si, Ge, Sn, Pb, Uuq
Nitrogen Group: N, P, As, Sb, Bi, Uup
Oxygen Group: O, S, Se, Te, Po
Halogens: F, Cl, Br, I, At
Noble Gases: He, Ne, Ar, Kr, Xe, Rn
Reactivity of Groups of
Elements:
Covalent Bonds
made
Alkali metals: Very reactive
Alkaline metals:
Transition metals: groups 3-12
Boron Group:
Carbon Group:
Nitrogen Group:
Oxygen Group:
Halogens:
very reactive
Noble Gases:
ionic charge
+1
+2
+3
makes 4 bonds
makes 3 bonds
makes 2 bonds
-1
Inert; does not react
Properties of Non Metals and
Semiconductors
Non-metals generally have properties opposite
to that of metals.
Semi-conductors conduct electricity and thermal
energy but not as good as metals.
Atomic Number
Each element has a unique and
specific number of protons
(The atomic number).
Mass Number: is the number of
protons and neutrons in the
nucleus.
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Atomic Number
The atomic number also tells
you how many electrons are in
the atom.
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Isotopes
An isotope of an element has has a
different but specific number of
neutrons in the nucleus.
Mass number - atomic number =
number of neutrons
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Chemical Reactions
Chemical reactions are
processes in which atoms are
rearranged into different
combinations of molecules.
Molecule: the smallest
complete unit of of a compound
that has te properties of that
compound.
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Physical Processes
Physical processes including
freezing and boiling, changes
the form or the arrangement of
the molecules of a material
with no chemical reaction.
Example: water forms ice (a
crystalline structure)
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Chemical Reactions
Reactant atoms and molecules interact to form products
(compounds) with different chemical properties than the
elements that compose the product.
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Conservation of Matter
Conservation of Matter: In
chemical reactions, the number
of atoms stays the same no
matter how they are arranged, so
their total mass stays the same.
Chemical Reactions
Most chemical reactions release (let go) or absorb
(take in) heat energy.
.
Balancing Equations
The number of atoms must be equal on both sides of
the equation. H2 + O2 = H20
Count the number of each atom on each side of the
equation. Remember to count subscripts as well.
2H + 2O = 2H + O
Oh No!
If the number does not match, you must use
coefficients (numbers placed in front of the chemical
symbols) to balance the equation. Count again.
2H2 + O2 = 2H2O
4H + 2O = 4H + 2O
o.k!
Acids & Bases
Acid: a substances that produces H+ ions in water.
Base: A substance that produces OH - ions in water.
A solution is acidic, basic, or neutral based on the pH
scale.
The pH Scale
Acidic: 1 - 6.9
Neutral: 7
Basic: 7.1 - 14
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Atomic Number
Each element has a unique and specific atomic
number (number of protons within the
nucleus).
An isotope of an element has has a different but
specific number of neutrons in the nucleus.
The Chemistry of
Living Systems
Carbon, because of its ability to
combine in many ways with
itself and other elements, has
a central role in the chemistry
of living organisms.
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The Chemistry of
Living Systems
Living organisms are made of molecules
consisting largely of:
carbon, C ex. Carbohydrates (C6H12O6)
hydrogen, H ex. Water (H20)
nitrogen, N ex. DNA
oxygen, O ex. Water
phosphorus P, and sulfur S.
The Chemistry of
Living Systems
Living organisms have many different kinds of
molecules, including small ones, such as
water (H20) and salt (NaCl), and very large
ones, such as carbohydrates, fats, proteins,
and DNA.
example: Glucose
(carbohydrate)
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Galaxies
Galaxies are clusters of billions of stars
and may have different shapes.
Types of Galaxies
Spiral Galaxy: has a bulge in the middle, and spiral
arms made up of gas, dust, and new stars.
The Milky Way, the galaxy we are in, is a
spiral galaxy.
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Elliptical Galaxy: are elliptical and slightly flattened.
Irregular Galaxy: have no definite shapes.
The Sun & Stars
The Sun is one of many stars in the Milky Way
(a spiral galaxy).
Stars may differ in size, temperature, and color.
Hot Stars are blue in color.
The coolest stars are red
in color.
The Sun is yellow in color
because its surface temperature
is 5000-6000 degress Celcius.
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The Sun & Stars
Stars are the source of
light for all bright objects in
outer space and that the
moon, comet, and
planets shine by
reflected sunlight, not by
their own light.
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Measures of Distance
Astronomical units (AU) the
average distance between
the sun and the Earth,
measures distances within
the Solar System.
Light years, the time it takes
light to travel in one year,
measures of distances
between the Earth and the
stars.
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Objects in
the Solar System
Objects in the Solar System orbit the sun and are
acted upon by gravitational force.
Planets: objects either terrestrial (dense & rocky) or gaseous
(made of gas) orbiting around the sun.
Planetary satellites (moons): terrestrial (dense & rocky)
orbiting around a planet.
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Objects in
the Solar System
Asteroids: dense and rocky
fragments (of a former planet)
located between Mars and
Jupiter. These fragments orbit
around the sun.
Comets: a rocky and icy object
orbiting in an elliptical path
around the sun.
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Distances of the Planets in
the Solar System
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The Solar System
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Graphing
The equation for a line is: y = kx.
Each x value has a unique,
corresponding
y value. X and Y values can be depicted
on a graph.
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Equation for a Line
The equation for a line is: y = kx.
k = the slope of a line, a constant
The slope of a line can be calculated by:
k = y/x
Distance vs. Time Graphs
The equation for a line is: y = kx.
k = the slope of a line, a constant
y = distance
x = time
The slope of a line or (the speed of an object) for any point on the
graph can be calculated by using any x point with its
corresponding y point:
k (speed) = y/x
or
distance/time
Solving Speed Problems
How far will an athlete travel in 30 minutes if she can run 9 km in 1 hr.
The equation for a line is: distance = (speed)(time)
y = kx.
The slope of a line or (the speed of an object) for any point on the
graph can be calculated by:
k (speed) = y/x or
9 km/1hr =
distance/time
9km/hr
y(distance) = speed x time = 9 km/hr x .5 hr = 18 km
Mass vs. Volume Graphs
The equation for a line is: y = kx.
k = the slope of a line, a constant
y = mass
x = volume
The slope of a line or (the density of an object) for any point on
the graph can be calculated by using any x point with its
corresponding y point:
k (density) = y/x
or
mass/volume
Solving Linear Equations
(when given data)
The equation for a line is: y = kx. k = the slope of a line
Data Given to you in a chart:
y
x
1.0 4N
y = distance of a
1.5 6N
spring scale
2.0 8N
x = force
Question: What will the distance of a spring scale (y) be if the
force (x) is 3.5?
The slope of a line or (the) for any point on the graph can be
calculated by using any x point with its corresponding y point:
k = y/x
k = 4N/1.0
k=4
Slope = 4
Solving Linear Equations
(when given data) cont….
The equation for a line is: y = kx. k = the slope of a line
The problem wants you to find the distance of a scale (y) if the
force (x) is 3.5. Plug in the value of the slope (4) and the x value
of 3.5 in the original equation for a line: y = k(x)
Since the slope is 4.0, you can calculate what the distance of a
spring would be if you use 3.5 in the equation of a line:
y = kx
y = 4(x) if x=3.5, then….
y = 4 x 3.5 or 15.
Identifying the Slope of a Line
The equation for a line is: y = kx. k = the slope of a line
When working with graphs for:
distance vs. time (speed)
mass vs. volume (density)
As long as the slope is a positive value:
On a graph with multiple lines, the line with the greatest slope is the line
closest to the Y axis.
On a graph with multiple lines, the line with the smallest slope is the line
closest to the X axis.
Identifying the Slope of a Line
for Distance vs. Time (Speed)
The equation for a line is: y = kx. k = the slope of a line
The graph below shows a constant or the same or a constant
distance traveled every second.
Meters (m)
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Seconds (s)
Identifying the Slope of a Line
for Acceleration
The equation for a line is: y = kx. k = the slope of a line
Important: This is an Acceleration graph! Speed vs. Time
or velocity vs. time.
Constant Speed = a straight line on the graph below.
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Solving Position vs. Time Problems
What is the speed of the object during the time interval from 4 seconds to
10 seconds: x1 = 4m, y1 = 0 s
x2=10m,
speed = distance/time
Speed = y2 - y1 / x2 - x1
=18 - 0/ 10 - 4
= 18/6
= 3 m/s
y2 = 18 s
distance in this case is y2-y1
time = x2 - x1