Forces, Waves, and Electricity

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Forces, Waves, and Electricity

• Georgia High School Graduation Test Science
  Review
• Mrs. Kirby

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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.

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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

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Distance versus Time Graph

• AKA position versus time graph
• Straight line represents constant (uniform) speed

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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

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Distance versus Time Graph Revisited

• Non-linear graph represents acceleration
• Parabola constant acceleration

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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

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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

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Determining the Net Force
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Newtons 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

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Newtons 2nd Law of Motion

• Force mass x acceleration
• F ma

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Newtons 3rd Law of Motion

• For every action, there is an equal but opposite
  reaction
• Examples
• Punch a wall, it punches back
• Rocket propulsion

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Gravity

• Gravity attractive force between two objects
  that have mass
• Makes falling objects accelerate (g 9.8 m/s2)
• Depends on mass and distance

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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.

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Mass versus Weight

• MASS
• measure of the amount of matter in an object
• measured in kilograms
• does not depend on location
• an objects 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 objects weight on Earth is more than its
  weight on the Moon

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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.

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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

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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

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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

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Types of Mechanical Energy

• Kinetic energy of motion
• Potential stored energy due to position

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Conservation of Energy
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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

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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.

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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).

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Sample Question 6

• How are frequency and wavelength related?
• Answer Frequency and wavelength are inversely
  related. High frequency waves have short
  wavelengths.

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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

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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.

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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.

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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

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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
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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

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Electricity

• Electrons carry a negative charge.
• Lost electrons positive charge
• Gained electrons negative charge
• REMEMBER
• Like charges repel
• Opposites attract

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Electrical Circuits
SERIES

• Current flows in a closed circuit
• Ohms Law
• V IR
• Two types of circuits
• Series (single path)
• Parallel (poly paths)

PARALLEL
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Electromagnet

• One can make an electromagnet with a nail,
  battery, and wire
• When current flows through the coiled wire, the
  nail becomes magnetized.

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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?

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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.

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Short Quiz Answers

• A force is a push or a pull. Unbalanced (net)
  forces result in acceleration.
• 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).
• Sound and ocean waves are both mechanical waves
  because they both require matter to transmit
  energy.
• 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.