Transcript Forces, Waves, and Electricity

Forces, Waves, and Electricity
Georgia High School Graduation Test:
Science Review
Ashley Kirby
Introduction
From the key vocabulary, circle
the words that you can already
define or use in a sentence.
Write down two or three things
that you think are important for
you to know today.
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
Sample Question #1
Use the equations for velocity and
acceleration to solve the following examples:
A ball rolls in a straight line very slowly across the
floor traveling 1.0 meter in 2.0 seconds. Calculate
the velocity of the ball.
Answer: v = 0.50 m/s
If the ball from the above question rolls to a stop in
2.0 seconds, calculate the acceleration
(deceleration) of the ball.
Answer: a = -0.25 m/s2
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
 Makes falling objects accelerate (g = 9.8 m/s2)
 Depends on mass and distance
Sample Question #2
What causes an object to accelerate as it
falls?
Answer: The force of gravity causes an object
to accelerate at a rate of 9.8 m/s2 toward Earth.
Mass versus Weight
MASS
WEIGHT
 measure of the amount  measure of the force of
of matter in an object
gravity on an object
 measured in kilograms  measured in Newtons
 does not depend on
 does depend on
location
location
an object’s mass on
Earth is the same as its
mass on the Moon
an object’s weight on
Earth is more than its
weight on the Moon
Sample Question #3
Explain the difference between mass and
weight.
Answer: Mass is the quantity of matter of an
object while weight is the measure of the force
of gravity on that object. Mass is conserved
while weight may change depending on
location.
Energy and Work
Energy = 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
Sample Question #4
Use the formula for work to solve the
following example:
A woman picks up her 10 Newton child lifting
him 1 meter. She then carries him 5 meters
across the room. How much work is done on
the child?
Answer: 10 Joules
• the 5 meters is not added to the 1 meter because the
distance moved (5 meters) is perpendicular to the force
applied
Types of Mechanical Energy
 Kinetic = energy of
motion
 Potential = stored
energy due to position
Conservation of Energy
Light
 Light is a form of electromagnetic radiation (EM)
 EM spectrum shows the forms of radiation in
order of increasing frequency (and energy) and
decreasing wavelength
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.
Sample Question #5
How are the frequency and wavelength
related to the energy carried by waves?
Answer: Higher frequency waves have more
energy while longer wavelength waves have
less energy. Frequency and energy are directly
related while wavelength and energy are
inversely related. Radio waves (long
wavelength) have less energy than gamma
waves (high frequency).
Sample Question #6
How are frequency and wavelength
related?
Answer: Frequency and wavelength are
inversely related. High frequency waves have
short wavelengths.
Electromagnetic Wave (EM) versus
Mechanical Wave
EM WAVE
 does not require
matter to transfer
energy
 CAN travel through a
vacuum
 example: light
MECHANICAL WAVE
 does require matter to
transfer energy
 CANNOT travel
through a vacuum
 example: sound
Sample Question #7
Compare electromagnetic and mechanical
waves.
Answer: Electromagnetic waves (light) do not
require matter to transfer energy while
mechanical waves (sound) require matter to
transfer energy. In other words, EM waves will
travel in a vacuum while mechanical waves will
not.
Reflection of Light
 When light strikes a
boundary, it reflects.
 The angle at which the
wave approaches a flat
reflecting surface is equal
to the angle at which the
wave leaves the surface
(like a bounce pass of a
basketball).
 Reflection results in
image formation.
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
Wave Interference
 the phenomenon
which occurs when
two waves meet while
traveling along the
same medium
 constructive =
waves add to produce
a larger wave
 destructive = waves
cancel to produce a
smaller wave
CONSTRUCTIVE
DESTRUCTIVE
The Doppler Effect
 observed whenever
the source of waves
is moving with
respect to an
observer
 an apparent change
in frequency occurs
 toward = higher
frequency
 away = lower
frequency
Electricity
Electrons carry a negative charge.
Lost electrons = positive charge
Gained electrons = negative charge
REMEMBER:
Like charges repel
Opposites attract
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.
Discussion
Aristotle claimed that objects fell at a
rate proportional to their weight, so
that heavier objects fell faster than
lighter objects. Explain why you think
he was correct or he was wrong. How
could one determine whether or not
he was correct?
Lesson Summarized
Write a sentence that explains the
system being discussed.
Draw a graphic organizer for each
system in this lesson. Show the
relationship of the parts of the
system to the whole within each
system.
Figure Reference
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Distance versus Time Graph figures: source unknown
Forces figure: retrieved from
http://www.glenbrook.k12.il.us/gbssci/phys/CLass/newtlaws/u2l2c
1.gif
Determining the Net Force figure: retrieved from
http://www.glenbrook.k12.il.us/gbssci/phys/CLass/newtlaws/u2l2d
11.gif
Newton’s Laws, Gravity, Work, Types of Mechanical Energy,
Conservation of Energy, Light, Interference, and Doppler Effect
figures: retrieved from http://www.physicsclassroom.com
Electrical Circuits figures: retrieved from
http://www.autoshop101.com/trainmodules/elec_circuits/circ101.ht
ml
Electromagnet figure: source unknown