Transcript Document 85607

Physics GHSGT Review
Speed and Velocity
• Speed = distance divided by time
s = d/t
• Units of speed = m/s
• Velocity = speed in a given direction
• Example:
– 55 mph = speed
– 55 mph north = velocity
Distance versus Time Graph
• AKA
position
versus time
graph
• Straight line
represents
constant
(uniform)
speed
Acceleration
• Acceleration = rate at which velocity
changes
• Involves a change in speed OR direction
a = (vf – vi )/ t
• Units of acceleration = m/s2
• Example: 0 to 60 mph in 5 seconds
• For acceleration to occur a net
(unbalanced) force must be applied
Distance versus Time Graph
Revisited
• Non-linear
graph
represents
acceleration
• Parabola =
constant
acceleration
Forces
• Force = a push or a pull
• Net Force = sum of all
forces acting on an
object
• Free-body diagram
shows all forces with
vector arrows
• Direction of force =
direction of acceleration
• Friction is a force that
always opposes motion
Determining the Net Force
Newton’s 1st Law of Motion
– An object at rest will
remain at rest and
an object in
constant motion will
remain in constant
motion unless acted
on by an
unbalanced force.
– Reason for
seatbelts
Newton’s 2nd Law of Motion
• Force = mass x acceleration
F = ma
Newton’s 3rd Law of Motion
• For every action,
there is an equal
but opposite
reaction
• Examples:
– Punch a wall, it
punches back
– Rocket propulsion
Gravity
• Gravity = attractive force between two objects
that have mass
• Depends on mass and distance
Effects of Mass and Distance on
Gravity
Momentum
• Momentum is mass in motion
p = mv
• To change an object’s momentum a
force must be applied
• Conservation of momentum states that
momentum before a collision equals
momentum after
Energy and Work
• The ability to do work
• Work = transfer of energy by applying a
force to move an object
W = Fd
where force and distance are in same
direction
• Both work and energy are measured in
Joules
Examples of Work and No Work
• Hammer applies
a force to move
the nail in the
same direction =
WORK
• Waiter applies a
force upward
while the tray
moves forward =
NO WORK
Types of Mechanical Energy
• Kinetic = energy of
motion
• Potential = stored
energy due to position
Conservation of Energy
Conservation of Energy
Conversion of Energy
• Motor = converts electrical energy into
mechanical energy
– Motors make fans Move which is Mechanical
• Generator = converts mechanical energy
into electrical energy
– Georgia Power use a Generator to provide
electricity
Power
• Power = rate at which
work is done
P = W/t
• Measure in Watts
• More work, less time
= More Power
• Less Work, Long time
= Less Power
Heat Energy
• Heat can be transferred through:
– Conduction = when objects touch
– Convection = when matter moves
– Radiation = in the form of waves
• Conductors = easily transmit energy
– Example: metals
• Insulators = do not easily transmit energy
– Example: gases such as air
Light
• Light is a form of electromagnetic radiation (EM)
• EM spectrum shows the forms of radiation in
order of increasing frequency and decreasing
wavelength
Energy of a Wave
• The energy transferred from a vibrating
source is carried by a disturbance in the
medium, not by matter moving from one
place to another.
– Waves move ENERGY, not matter
• Energy carried by a wave consist of KE
and PE
Parts of Wave
• The dashed lines represent the equilibrium
• The crests are the highest parts of the wave (letters A
and F)
• The troughs are the lowest parts of a wave (letters D
and I)
• Wavelength is the distance from crest to crest (A to F)
or trough to trough (D to I)
• Amplitude is the distance from the midpoint to the
crest
Wavelength
crest
trough
Wavelength
Transverse Waves
Transverse wave: a wave with a vibration
at right angles to the direction the wave
is traveling.
 The energy moves through the medium left
to right, but the motion of the wave is up
and down
 Makes an “S” shape wave
 Ex: light waves, string instrument
Longitudinal Waves
Longitudinal wave: a wave in which the
vibration is in the same direction as
that which the wave is traveling.
 Both the energy motion and the movement
of the wave are left to right
 Makes a pulse through the wave
 Ex: sound waves, earthquake waves
Doppler shift
• The doppler shift a a change in frequency
of a wave based on the movement of the
observer or the source
– Ex: a siren changing pitch as it moves
towards or away from you
http://www.colorado.edu/physics/2000/applet
s/doppler2.html
http://www.colorado.edu/physics/2000/applet
s/doppler.html
A Sound Wave
• Sound waves are longitudinal waves.
• Parts of a sound wave:
1) Compression: areas of high pressure
2) Rarefaction: areas of low pressure
• As a source vibrates in a periodic fashion, a series
of compressions and rarefactions is produced
• For all wave motion, it is not the medium that
travels across the room, but a pulse (or energy)
that travels.
• The speed of sound varies in different
media. In general, sound is
transmitted faster in liquids than in
gases, and still faster in solids.
• Remember that sound DOES NOT
travel through a vacuum
The EM Spectrum
• All of the EM waves are the same in nature,
differ only in the wavelength and frequency
“Ronald McDonald Is Very Ugly X-tra
Gross”
• The speed of light is constant when it
travels through one type of medium.
– Light travels faster in air than in water.
– Molecules in its way slows light down
– It is the opposite of sound waves, which
require a medium to move faster
• Light travels the fastest in a vacuum and
slowest in a solid
– The more molecules in its way, the slower it
goes
– Vacuum > G > L > S
Color of Light
• We see different colors depending on the
frequency of light emitted or reflected
• This is the reason blue flames are hotter than
yellow. Blue has a higher frequency so more
energy.
Mixing Colored Light
• Light of all the visible frequencies mixed
together produces white light.
• White light can also be produced by mixing
red, blue, and green light.
– Red, blue, and green are the 3 primary colors of
light.
• Color T.V.s produce all the colors we
perceive by combining red, blue, and green
light in a variety of ways.
Adding Primary Colors
•
•
•
•
Red + Green = Yellow
Red + Blue = Magenta (Purple)
Blue+ Green = Cyan (Aqua)
Red + Blue + Green = White
Refraction of Light
• Light waves travel
faster in air than in
water and slower in
glass than water.
• More dense =
slower light
• When light enters a
different medium,
speed changes and
it bends.
• Bending of light due
to change in speed
= REFRACTION
Electricity
•
•
•
•
Electrons carry a negative charge.
Lost electrons = positive charge
Gained electrons = negative charge
REMEMBER:
– Like charges repel
– Opposites attract
• An object can be charged through:
– Friction (rubbing two objects together)
– Conduction (touching a charged object to an
uncharged object)
– Induction (holding a charged object near an
uncharged object)
Electrical Circuits
SERIES
• Current flows in a
closed circuit
• Ohm’s Law
– V = IR
• Two types of circuits:
– Series (single path)
– Parallel (poly paths)
PARALLEL
Electromagnet
• One can make an electromagnet with a nail,
battery, and wire
• When current flows through the coiled wire, the
nail becomes magnetized.
Electromagnetic Induction
• Occurs when a current is produced by
moving a conducting wire through a
magnetic field
Radioactive Half-Life
Half-life: The time required for half of the
atoms of a radioactive isotope of an
element to decay.
– Radioactive isotopes decay at different rates
– The amount of a substance halves every halflife
– Ex: If the half life of an isotope if 10 years,
then after 10 years there is only half left. After
20 years, there is only half of that half (or 1/4th
left)