Forces, Waves, and Electricity Georgia High School Graduation Test: Science Review Mrs. Kirby.
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Transcript of Forces, Waves, and Electricity Georgia High School Graduation Test: Science Review Mrs. Kirby.
Forces, Waves, and Electricity
Georgia High School Graduation Test: Science Review
Mrs. 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/tUnits of speed = m/sVelocity = speed in a given directionExample:
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 measure of the amount
of matter in an object measured in kilograms does not depend on
location an object’s mass on
Earth is the same as its mass on the Moon
WEIGHT measure of the force of
gravity on an object measured in Newtons does depend on
location 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 chargeGained electrons = negative chargeREMEMBER:
Like charges repel Opposites attract
Electrical Circuits
Current flows in a closed circuit
Ohm’s Law V = IR
Two types of circuits: Series (single path) Parallel (poly paths)
SERIES
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.
Short Quiz Answers
1. A force is a push or a pull. Unbalanced (net) forces result in acceleration.
2. The object ejected from a spacecraft near Earth will most likely fall into the Earth due to gravity while the object ejected in deep space will travel at a constant speed until acted on by an unbalanced force (Newton's First Law of Motion).
3. Sound and ocean waves are both mechanical waves because they both require matter to transmit energy.
4. Light and sound both transfer energy, but light does not require matter to transfer energy while sound does. In other words, light waves will travel in a vacuum while sound waves will not.