Transcript TAKS Objective 5 - Dripping Springs ISD

TAKS Objective 5
PHYSICS
General Tips for TAKS Science:
• USE THE FORMULA CHART
– Here’s how:
• The TAKS does not expect you to know how to do every
Science problem, that’s why they give you a formula chart
• If you see a TAKS Science question with any numbers in
it, get out the formula chart, read the question then re-read
the question. Look for a formula that might go with the
question.
• For each number you are given, explore the words
immediately around it to determine where to plug the
number into the equation.
Example 1:
A car traveled 150 km in 2.5 hours.
What was its average speed in km per
hour? Record and bubble in your
answer on the answer document.
General Tips for TAKS Science:
• DON’T FORGET THE PERIODIC TABLE
– Any time you see the name of an element in a
question, or a word you even suspect to be an
element name, get out the periodic table
– Also, get out the periodic table if you see any
of the following words in a question:
•
•
•
•
•
•
“group”
“period”
“atomic mass”
“atomic number”
“protons” “neutrons” “electrons”
“valence”
Example 2:
According to the periodic table, which
element most readily accepts electrons?
A Fluorine
B Nitrogen
C Arsenic
D Aluminum
General Tips for TAKS Science
• There are a lot of vocabulary words in
Science, you should study vocabulary to
prepare for the Science TAKS. This is
especially important for Objectives 2 and 3
(BIOLOGY)
• IF YOU DO NOT KNOW A WORD:
– Don’t panic! Use context clues and try to
figure out what the word means.
– Don’t get hung up on words you don’t know.
Instead, focus on the words that you DO know,
and try to make sense of the rest using what
you know.
What does Objective 5 have in it?
• Questions about the motion of objects or
people.
• Questions about energy and energy
conservation
• Questions about heating and cooling
• Questions about light, sound, and waves
• MOST of the math-related questions on the
Science TAKS test come from Obj. 5
Motion:
Time, Distance, Speed, Acceleration
Time and Distance
• The SI unit for time is seconds
• The SI unit for distance is meters
SPEED
• Also known as VELOCITY
• Formula: speed = distance / time
• Common units:
– m/s – meters per second
– mi/hr – mph – miles per hour
Example 3: Speed/Velocity
The picture shows the position of a ball every 0.25 second on a
photogram. Using a ruler, determine the velocity of the ball.
F 3.5 cm/s
G 10.5 cm/s
H 14.0 cm/s
J 28.0 cm/s
Acceleration
• The rate of change in speed
• When an object “speeds up” that’s positive acceleration
• When an object “slows down” that’s negative
acceleration, or deceleration
• Formula:
Acceleration =
final velocity – initial velocity
change in time
Acceleration
• Common units for acceleration include:
– m/s2 - “meters per second squared”
– mi/hr2 – “miles per hour squared”
*Generally
the units for acceleration will be
______ per _______ squared.
Example 4: Acceleration
• What is the acceleration of a race car that speeds up
from 150 mph to 200 mph over 4 seconds?
A.
B.
C.
D.
-12.5 mi/hr2
12.5 mi/hr2
-5.3 mi/hr2
5.3 mi/hr2
Newton’s Laws of Motion
Things keep doing
what they were doing.
Newton’s 1st Law:
An object at rest tends to stay at rest
and an object in motion tends to stay
in motion with the same speed and in
the same direction unless acted
upon by an unbalanced force.
Newton’s Laws of Motion
The Law of Inertia in Everyday Life:
– When you slam on the breaks in a car, the car
begins stopping, but you and the belongings in
the car keep going, that’s why you have a
seatbelt.
What is an unbalanced force?
Balanced forces:
UN-balanced forces:
Newton’s Laws of Motion
Newton’s Second Law: The Force Equation
“The acceleration of an object is inversely
proportional to its mass and directly
proportional to its force.”
FORMULA: F = ma
“Force equals mass times acceleration”
A little bit more on force:
• The units for force are Newtons (N)
• 1 Newton = 1 (kg*m)/s2
Example 5: Force
Newton’s Laws of Motion
Newton’s 3rd Law:
“For every action there is an equal and
opposite reaction.”
For example:
When you step out of a boat in the
direction of the shore, the boat tends
to slide backwards in the direction of
the lake.
Example 6: Newton’s Laws
Momentum
• Momentum can be defined as “mass in motion”
• Momentum depends on two variables:
– How much stuff is moving (mass)
– How fast that stuff is moving (velocity)
Formula: Momentum = mass * velocity
or p = m * v
Conservation of Momentum
• CONSERVED = not changing or “constant”
• The Law of Conservation of Momentum states:
– “When two objects collide, the total momentum
before the collision must equal the total momentum
after the collision”
Conservation of Momentum
Real-life example:
– If two football players, a
defensive tackle, and a
running back collide on
the field the resulting
momentum will be the
same as the sum of both
players’ individual
momentums before the
tackle takes place.
Example 7: Momentum
Work
• “a force acting upon an object to
cause a displacement”
• Work is the force applied over a
distance
• The formula for work is:
or
Example 8: Work
Power
• Power is the rate at
which work is done
• The unit for power is
the watt
• 1 watt = 1 (N*m)/s
• When we say that
something is “powerful”
we mean it is both
STRONG and FAST
Power
For instance, you can pull
a refrigerator box 100
meters, or you can set it
in the back of a truck
and let the truck carry it
100 meters. Both the
truck and you could do
the same amount of
work, but the truck can
do it much faster. The
truck is more powerful.
Example 9: Power
Mechanical Energy
• Mechanical energy is the energy an object
has due to its motion (kinetic) or its stored
energy of position (potential)
Conservation of Energy
• Remember that “conserve” means “to not
change” or “to keep constant”
• The Law of Conservation of Energy states that
energy can be neither created, nor destroyed
• In other words, energy doesn’t disappear, it
just changes forms. When you hold a book up
in the air, it has potential energy. When you
drop the book, as it falls it has kinetic energy.
The potential energy wasn’t destroyed, it just got
changed into kinetic energy.
Example 10: Energy
Different Forms of Energy
• There are many forms of energy. Some
examples are:
–
–
–
–
–
Chemical (stored)
Gravitational potential energy (stored)
Thermal energy (kinetic)
Sound energy
Solar energy
Example 11: Energy
Machines
• Machines are used to change a small force
into a larger one, change direction of the
force to make it more useful
• Simple machines: levers, ramps, wheels,
pulleys and screws
• Complex machines are made up of several
or many simple machines
• Mechanical advantage: the amount by
which a machine multiplies the force
Example 12: Mechanical
Advantage
Efficiency
• Machines are not 100% efficient so
some work done is lost to things like
friction.
• The work you put in to a machine is
called “work input”
• The work the machine actually does is
called “work output”
Example 13: Efficiency
WAVES
WAVES
• There are many different kinds of
waves. A few examples are:
– Sound waves, visible light waves,radio
waves, microwaves, water waves, sine
waves, cosine waves, telephone chord
waves, stadium waves, earthquake waves,
waves on a string, and slinky waves
• On a molecular level, waves are
disturbances that travel through a
medium (for instance air) via one
molecule bumping into and vibrating
the next
The Parts of a Wave
Amplitude
Period and Frequency of Waves
• The period of a wave is the time it takes for
one point on the wave to go through one
vibration. In other words, to go from rest to
crest to trough and back to crest.
• The units for period are seconds (s)
• The frequency of a wave is the number of
vibrations that occur per second
• The units for frequency are Hertz (Hz)
Wave Velocity
• The velocity of a wave can be found by
multiplying the frequency by the
wavelength.
Example 14:
Wave Velocity
Interference
• When two waves collide, they either add to
one another, or cancel each other out
• Waves intersecting or colliding is called
“interference”
Destructive
Constructive
Light
• Light travels on electromagnetic waves
• There are wavelengths of light that humans
can see, and wavelengths that we can’t.
The wavelengths we can see are referred to
as the visible light spectrum.
Light
• You learned in biology that plants contain a green
pigment called chlorophyll. Plant leaves appear
green to the human eye because they reflect green
light –all of the other colors are absorbed.
• General rule: Objects appear to be the color that
they reflect, not the colors they absorb
Example 15: Color
Light
• Certain smooth surfaces will reflect light
(like mirrors, or the surface of a pond)
• Sometimes light waves will move from one
medium into another, like moving from the
air into water. When light crosses a
boundary such as that between air and
water, the light wave gets refracted, or
“bent”
Light
• Surfaces that are not smooth will not reflect
light in a consistent or predictable manner.
Instead they cause the light to be dispersed
into all different directions
• For instance, if you shine a light on a
mirror, you see the beam come back off of
the mirror. However, if you shine a light on
a sweater you will not see a reflected beam.
The uneven surface of the sweater will
cause the light to be dispersed.
Example 16: Light
Sound
•Sound travels on waves that are interpreted by
the inner ear
•Vibrations disrupt air molecules around the
source of the vibration, causing sound
•The pitch of the sound heard is determined by
the frequency of the vibrations (i.e. faster
vibration = higher frequency = higher pitch)
Example 17: Sound
Heat Energy Transfer
Heat Transfer
• Thermal energy, or heat energy, is the result of
particles of matter moving (remember kinetic
energy?)
• Heat energy can be transferred from one medium
to another in three main ways:
– Conduction
– Convection
– Radiation
Conduction
• In the process of conduction, heat moves
through a substance or from one substance to
another by the direct contact of molecules
• Here’s how it works:
Fast moving molecules collide with slow moving
molecules. This causes the slow moving
molecules to move faster. Now, these molecules
collide with other slow moving molecules causing
them to move faster. This process is repeated
over and over. In this way heat energy is
transferred from molecule to molecule all the
way through a substance.
Conduction
• Some substances conduct heat better than others.
These are referred to as conductors.
• Substances that do NOT conduct heat well are
known as insulators.
• For example: The reason wooden spoons are used
when cooking instead of metal spoons is because
the wooden spoons are good insulators. Because
metal spoons are good conductors they heat up
quickly and can easily burn their users.
Convection
• Warm air rises. Cool air sinks. When gases or
liquids warm up they transfer the heat upward
and outward from their sources.
Radiation
• Radiation is the transfer of energy by
electromagnetic waves
• Examples:
– Feeling the sun on your face
– Feeling the warmth of a campfire while sitting
around the campfire
Convection, Conduction, and Radiation
Example 18: Heating and
Cooling