Download Ideal mechanical advantage = effort length resistance length

THE ATOM
SUBATOMIC PARTICLES
Nucleus is the center of the atom, has a positive charge, contains 99.9% of the mass (protons + neutrons) of the atom, holds neutrons
and protons. The atom is mostly empty space.
- Proton, p+: has a positive charge, all are identical, no matter which element, mass is one amu, the number of protons determines
which element you have…represented by atomic number.
- Neutron, n°: has a neutral (no charge), all are identical, regardless of the element, mass is one amu, the number of neutrons of
an element can be determined by: Mass Number – Atomic Number = neutron number.
Electron Cloud is the area surrounding the nucleus, mostly empty space, holds the electron
- Electron, e-: has a negative charge, the mass is 1/1840 amu (atomic mass unit), in a neutral atom, the number of electrons equals
the number of protons
ATOMIC NUMBER, Z: Equals the number of Protons, determines the identity of the element, if you change the number of protons,
you change the element
MASS NUMBER, A:
ATOMIC MASS:
The number of protons and neutrons combined, different for each isotope of an element
All masses of the isotopes of the element averaged together. It is never a whole number.
Arrange the elements above from least to greatest atomic mass.
Place the above in order from least to greatest concentration of atomic mass.
“A” represents the nucleus.
SUMMARY:
Particle
PROTON
Location
nucleus
Charge
positive
NEUTRON
nucleus
neutral
ELECTRON
electron cloud
negative
Mass (amu)
1
1
1/1840
the number in a neutral atom
same as the atomic number
mass number – atomic number
same a protons in a neutral atom
PERIODIC TABLE ORGANIZATION
The periodic table is organized by increasing atomic number and is read from left to right.
Each vertical column is called a group or family. All elements in the same family have the same number of valence electrons.
Each horizontal row is called a period. All elements in the same period have the same number of energy levels.
The Element Families
Family 1 (1A)
Alkali Metal family
+1 ion
1 valence electron
Family 2 (2A)
Alkaline Earth Metals
+2 ion
2 valence electrons
Elements in the first two columns are reactive metals and form compounds easily.
Family 13 (3A)
Boron family
+3 ion
3 valence electrons
Family 14 (4A)
Carbon family
+4 or -4 ion
4 valence electrons
Family 15 (5A)
Nitrogen family
-3 ion
5 valence electrons
Family 16 (6A)
Oxygen family
-2 ion
6 valence electrons
Family 17 (7A)
Halogen family
-1 ion
7 valence electrons
The halogen nonmetals are very reactive.
Family 18 (1A)
Nobel Gas family
no ion
8 valence electrons
The Noble Gases are very UNREACTIVE (inert) and stable because their outermost energy level is full (8 electrons).
ISOTOPES
An isotope is when you have atoms of the same element that differ in atomic mass. These atoms have the same number of
protons but a different number of neutrons. Mass numbers are the way you distinguish one isotope from another. Any sample of an
element in nature will contain a mixture of isotopes for that element.
Example:
CARBON
carbon-12
carbon-13
carbon-14
6 protons 6 neutrons
6 protons 7 neutrons
6 protons 8 neutrons
Carbon-14 and Carbon-13 atoms’ are not as stable as carbon-12 and easily break down.
If an isotope has too many or too few neutrons compared to the number of protons, it is unstable and will undergo radioactive decay.
These radioactive isotopes become different elements in an effort to become more stable.
SOLUTIONS
A solution is different from other types of matter like an element, compound, or mixture. A solution is a mixture of two or more
substances where all parts are identical. The parts will not settle out upon standing and cannot be filtered. Yet, they are not
chemically combined like in a chemical reaction. They were just mixed together in any amount. Examples include tea, coffee, and
sterling silver
There are two parts to a solution, the solute (substance being dissolved) and the solvent (substance doing the dissolving). The solute
is in the lesser amount and the solvent is in the greater amount. Water is the universal solvent because it dissolves a lot of things.
A solution is saturated when it is holding all the solute that is can at that temperature. So a glass of tea that has sugar sitting at the
bottom of the glass is saturated because it cannot hold any more sugar in solution. The excess sugar is sitting at the bottom of the
glass. When a solution can dissolve more solute it is said to be unsaturated.
Acids and bases
The further left …the stronger the
acid…1 is strongly acidic and 5 is
mildly acidic.
The further right …the stronger the
base…14 is strongly basic and 10 is
mildly basic.
Scientists use something called the pH scale to measure how acidic or basic a liquid is. Although there may be many
types of ions in a solution, pH focuses on concentrations of hydrogen ions (H+) and hydroxide ions (OH-).
Acid: A solution that has an excess of H+ ions. It comes from the Latin word acidus that means "sharp" or "sour".
Base: A solution that has an excess of OH- ions. Another word for base is alkali. Bases taste bitter and feel slippery
Aqueous: A solution that is mainly water. Think about the word aquarium. AQUA means water.
Strong Acid: An acid that has a very low pH (0-4).
Strong Base: A base that has a very high pH (10-14).
Weak Acid: An acid that only partially ionizes in an aqueous solution. That means not every molecule breaks apart. They
usually have a pH close to 7 (3-6).
Weak Base: A base that only partially ionizes in an aqueous solution. That means not every molecule breaks apart. They
usually have a pH close to 7 (8-10).
Neutral: A solution that has a pH of 7. It is neither acidic nor basic.
Neutralization reaction: when an acid and a base react together (mixed) a salt and water is formed.
RADIOACTIVITY AND HALF-LIFE
HALF-LIFE
Each radioactive element breaks down after a certain amount of time. This time is measured in “half-life”. A half-life is the
time required for one half of the substance’s atoms to break down. The half-life for a substance does not change. Some examples are
carbon-14 (half-life of 5730 years) and uranium-238 (half-life of 4.5 billion years). When asked to work a half-life problem, draw the
boxes, like the ones below, to help you answer the question.
All atoms are
radioactive
One half-life later,
half are radioactive
Two half-lives later,
¼ are radioactive
Three half-lives later,
1/8 are radioactive
RADIATION
The unstable elements tend to break down spontaneously. They do not have enough “binding energy” in their nuclei to hold
the protons and neutrons together. Most radioactive nuclei have too many neutrons compared to their protons. These elements are
said to be radioactive. Radioactivity is where rays are spontaneously produced by the nucleus of an unstable atom. It can be
particles, energy, or a mixture of both.
Types of Radioactive Decay:
- Alpha Particle, : Has a +2 charge; the particle is composed of two protons and two neutrons; Is stopped by skin,
tissue paper. These particles are not very energetic. The atomic number drops by two. It is sometimes written as a
helium atom: 42 He
Example: When uranium (atomic number 92) undergoes radioactive decay, it gives off an alpha particle. The atomic
number drops by two and it becomes the element, thorium, with an atomic number of 90.
- Beta Particle, : Has a –1 charge; comes from a neutron being given off – the neutron gives off a beta particle
(negative) and a proton (positive); the beta particle leaves and the proton stays in the nucleus. Metal foil stops this
particle. The atomic number increases by one.
Example: When bismuth (atomic number 83) undergoes radioactive decay, it gives off a beta particle. The atomic
number increases by one and it becomes the element polonium, with an atomic number of 84.
-
Gamma Ray, : Has no mass or charge because it is energy. It is high-powered electromagnetic radiation and it is
stopped by lead, concrete.
Uses of Radioactivity
- Medicine: Radiation is used as a form of therapy for cancer. X-rays and gamma rays produced by cobalt-60 or cesium-137.
Radioactive elements can be used as tracers that can follow certain chemical reactions inside living organisms.
- Industry: Food may be exposed to gamma rays in an effort to kill bacteria and other parasites in the food in hopes to limit the
number of food poisoning cases.
- Radiochemical Dating: Radioactive isotopes are used to measure fossils and other artifacts. While an organism is alive, it takes
in isotopes. Once the organism dies, the isotopes do not enter the body anymore. Scientists can estimate how much of the
radioactive isotope was present in the body to begin with and then determine how much is currently left. Carbon-14 is a common
isotope measured.
- Too much radiation can be lethal. You are exposed to radiation every day by watching television, standing in the sun, and even
standing in your basement. The goal is to not get exposed to too much radiation. Too much radiation can result in cancer or other
diseases. This happens when the radioactive substance causes damage to your DNA and chromosomes. This damage to the DNA
is called mutations. This in turn causes changes in your cells.
- Fuel/Electrical Source: The energy produced in nuclear reactions can be used as a fuel source. Fusion is the result of nuclei
combining and giving off huge amounts of energy. This occurs in the sun. Fission is the splitting of an atom into two and
releasing energy at the same time.
STATES OF MATTER
SOLID---Solids have definite shape and definite volume. For the most part, solids can be carried around without the help of a special
container. The molecules or atoms in a solid are densely packed together and vibrate back and forth in their own space. The atoms
cannot change positions. Examples: rock, paper.
LIQUID---Liquids have no definite shape and a definite volume. They take on the shape of the container that they are in. The
molecules or atoms in a liquid are packed together, but not as densely as a solid. They can slide around each other but cannot break
apart. Examples: water, mercury.
GAS---Gases have no definite shape and no definite volume. They expand to take on the shape and volume of the container they are
in. A gas’ molecules or atoms have more energy than a solid or liquid and they can go anywhere within their container. Examples:
helium, air.
PHASE CHANGES
Each of the three main states of matter can change into another state by going through a phase change. Substances are made
to change phases by adding or taking away heat energy. There are six phase changes.
Melting
Vaporization (boiling)
Sublimation
solid becomes liquid
liquid becomes gas
solid becomes gas
absorbs heat
absorbs heat
absorbs heat
ENDOTHERMIC
Freezing
Condensation
Deposition
liquid becomes solid
gas becomes liquid
gas becomes a solid
loses heat
loses heat
loses heat
EXOTHERMIC
Be sure you understand a heating curve. See below:
G
L
Temp.
S
Energy
Phase changes are physical changes. Physical changes do not produce a new substance. They produce the same substance with new
physical properties. For instance, water may change from a solid to a liquid. Its volume and density will change, but it is still water.
Examples of physical changes include melting, freezing, condensation, vaporization, sublimation, cutting, breaking, mixing, and
dissolving.
Chemical properties cannot be observed unless the substance you are observing becomes something new. The particles of
one substance undergo a chemical change and become something new. Chemical properties include such properties as flammability.
You cannot observe this in paper unless the paper burns. Then, it is no longer paper.
There are several evidences of chemical changes. We also call these chemical reactions. These are:
- Formation of a new substance (solid precipitate, gas bubbles)
- The production of energy (heat or light)
- The absorption of energy
- Appearance of a new color or odor
Examples of chemical changes include combustion (burning), fermentation, metabolism, electrolysis, rusting – anything that involves
a chemical reaction.
TRANSFORMING ENERGY
Energy is the ability to do work (work involves a change in movement). Energy is the ability to cause change. The units for
energy are joule, J. All matter contains some form of energy because all matter has the ability to do work or cause change.
There are changes in forms of energy. This is where energy changes from one type to another. Energy cannot be created or
destroyed, just converted from one form to another. When you rub your hands together, mechanical energy (moving your arms) turns
into heat energy in your hands due to friction.
MECHANICAL
HEAT
CHEMICAL
ELECTRICAL
LIGHT
associated with motion. Ex. waterfall, sound, running.
internal motion of particles of matter. The faster the particles move, the more heat energy is present Ex.
rubbing hands together.
stored in bonds that hold atoms and ions together. Ex. fire, energy to move muscles
moving electrical charges. Ex. lightning, radio
visible portion of the electromagnetic radiation
Examples of Changes from One Form of Energy to Another
Chemical to electrical
Flashlight battery
Electrical to heat
toaster
Electrical to sound
telephone, door bell
Electrical to chemical
human sight
Electrical to mechanical
turning on a ceiling fan
Chemical to mechanical
energy in food helping your arms move to throw a ball
Mechanical to electrical
water turning a turbine which then moves a magnet to generate electricity
HEAT TRANSFER
Heat is energy, sometimes called thermal energy. The heat of an object is the total kinetic energy of the random motion of its
atoms and particles. When a substance is heated, its molecules move faster and further apart. Heat is always transferred from the
hotter object to the cooler object. Dark colored objects absorb more heat than light colored objects. That is the reason tennis players
wear white!
Conduction:
Heat is transferred from one object to another by direct contact. The two substances must be touching. An example
of conduction is the hot chocolate heating the cup it was poured into. Substances that are conductors transfer heat very easily - iron,
copper, and aluminum. Insulators slow down the conduction of heat - air and glass.
Convection:
Heat is transferred through currents of liquids and gases. As a fluid gets warmer, its molecules spread out and
become less dense. This fluid will rise because it is now less dense than the fluid on top of it. As it rises, colder fluids fall. This cycle
forms a current of warm rising fluid and cold falling fluids. This is called convection current. Water circulating in the oceans or
world wind currents is examples of this type of heat transfer.
Radiation:
This type of heat transfer requires no matter. Radiant heat is the transfer of energy by electromagnetic (infrared)
waves. Examples of radiation are when you feel the heat from the fire or the sun’s heat on your face.
FORCES
A force is a push or pull that starts, stops, or changes the direction of an object. Force transfers energy to an object. To
determine the amount of force being used, you need the mass of the object and its acceleration. Force is measured in Newtons, N.
The equation is:
Force = mass x acceleration (F=ma)
Forces that are in opposite directions and equal in size are called balanced forces. The larger arrow indicates in which direction the
object will move.
A
+
=
If the two forces are exerted in the same direction, they
combine and should be added together (A).
B
+
=
0
When forces are balanced, there is no change in
motion (B).
C
If the forces are exerted in exactly opposite
directions and are not equal in size, then you
must subtract the smaller force from the
larger to get the net force (C).
Friction is a force that opposes motion. It slows down an object. Motion of an object is going to occur when the forces
acting upon it are unbalanced, like in Figure C. One force cancels out the effects of a smaller force. There are three types of friction:
fluid friction, rolling friction, and sliding friction. Fluid friction has the least amount of force and sliding has the most.
NEWTON’S FIRST LAW (Law of Inertia)
Newton’s first law states that an object in motion will remain in motion and an object at rest will remain at rest unless acted
upon by an unbalanced force.
An object placed on a desk stays there until someone or something pushes it off. A ball thrown in space will continue forever until it
hits something. But a ball thrown on earth will not. The ball thrown on earth is acted on by gravity and friction. So it slows down
and falls to earth. Gravity and friction are the unbalanced forces.
The more mass an object has, the more inertia an object has. An object with a lot in inertia is difficult to get moving and also
harder to stop once it is moving.
NEWTON’S SECOND LAW
Acceleration is produced when a force acts on a mass. The greater the mass (of the object being accelerated) the greater the amount of
force needed (to accelerate the object).
NEWTON’S THIRD LAW
For every action there is an equal and opposite re-action.
Rocket
This means that for every force there is a reaction force that is equal in size, but opposite in direction. That is to say that whenever an
object pushes another object it gets pushed back in the opposite direction equally hard.
GRAVITY
The universal Law of Gravitation states that every object in the universe is attracted to every other object in the universe.
This force of attraction depends on the mass of the two objects as well as the distance that separates them. The more mass it has, the
greater its gravitational force. The closer the two objects are, the greater the gravitational force. On earth, when you let go of an
object, it falls to the ground at 9.8m/s2. This is acceleration due to gravity. Objects accelerate as they fall due to gravity.
Gravity is measured by weight and the unit is the Newton, N. If you change the force of gravity, you will change the weight.
Keep in mind that the amount of matter – the mass – does not change - only the force that is pulling on that matter changes and this is
reflected in a change in weight. Weightlessness occurs when the force acting upon an object is equal and opposite to the force of
gravity.
WORK
Force is needed to move an object and in doing so, work is done. In order for work to be done, you must be lifting
something. Lifting a book is work. Simply carrying the book across the room or holding the book above your head is not considered
work. There must be a change in disatance.
The equation is: Work = Force x distance (W=FD)
The unit for work is joules (J)…also known as a Newton-meter.
MACHINES
A machine is a device that makes work easier. A machine makes work easier by changing the direction or the size of the
force needed to do work. Remember work is calculated by force times distance. If you change force or distance, the amount of work
will change. EFFORT FORCE is the amount of force that is applied to the machine by you. The force opposing the effort force is
the RESISTANCE FORCE - often the weight of the object.
Mechanical advantage is the number of times a machine multiplies force. It is the ratio of the force that comes out of a
machine to the force that is put into the same machine. To formula for mechanical advantage is:
Actual mechanical advantage = resistance force  effort force.
The actual mechanical advantage is different from the ideal mechanical advantage. The ideal mechanical advantage is calculated by:
Ideal mechanical advantage = effort length  resistance length
There are six simple machines. One group includes the inclined plane (ramp), the screw, and the wedge. The second group
includes the pulley, the wheel and axle, and the lever.
A compound machine is a combination of two or more simple machines. The mechanical advantage of a compound machine
is greater than that of just one simple machine. Example: mechanical pencil sharpener - inclined plane, a wheel and axle.
There are three classes of levers representing variations in the location of the fulcrum and the input and output forces.
First-class levers
Examples:
1. Seesaw (also known as a teeter-totter)
2. Crowbar
3. Pliers (double lever)
4. Scissors (double lever)
Second-class levers
Examples:
1. Wheelbarrow
2. Nutcracker (double lever)
3. The handle of a pair of nail clippers
4. An oar
Third-class levers
Examples:
1. Human arm
2. Tongs (double lever) (where hinged at one end, the style with a central pivot is first-class)
3. Catapult
4. Any number of tools, such as a hoe or scythe
5. The main body of a pair of nail clippers, in which the handle exerts the incoming force
MECHANICAL ADVANTAGE OF THE INCLINED PLANE
If an object is put on an inclined plane it will move if the force of friction is smaller than the combined force of gravity and
normal force. If the angle of the inclined plane is 90 degrees (rectangle) the object will free fall.
A pulley is a wheel with a groove along its edge, for holding a rope or cable. Pulleys are usually used in sets designed to
reduce the amount of force needed to lift a load. However, the same amount of work is necessary for the load to reach the
same height as it would without the pulleys. The magnitude of the force is reduced, but it must act through a longer
distance. Pulleys are usually considered one of the simple machines.
Types of Pulleys
movable pulley
 A fixed pulley has a fixed axle and is used to redirect the force in a rope (called a belt when it goes in a full circle).
o A fixed pulley has a mechanical advantage of 1.
 A movable pulley has a free axle, and is used to transform forces - when stationary the total force on the axle
balances the total force provided by the tension in the rope (which is constant in magnitude in each segment). As
illustrated below, if one end of a rope is attached to a fixed object, pulling on the other end will apply a doubled
force to any object attached to the axle.
o A movable pulley has a mechanical advantage of 2.
compound pulley
Block and tackle

A compound pulley is a system of movable pulleys. The mechanical advantage can be increased by using a block
and tackle, where there are several pulleys on each axle. Plutarch reported that Archimedes moved an entire
warship, laden with men, using compound pulleys and his own strength.
MOTION
In order for motion to occur, there must be unequal forces. To measure motion, calculate the speed of the object.
The formula for speed is: Speed = distance  time
The speed and direction of an object’s motion is called velocity. Constant speed means that the object is not changing its
motion. Average speed can be calculated by taking the total distance traveled divided by the total time elapsed.
Velocity is speed in a particular direction. There are times when an object needs to change its velocity. This is done by slowing
down or speeding up. Once motion gets started, unequal forces allow for speeding up or slowing down. “Speeding up” is called
acceleration. Negative acceleration is called deceleration (“slowing down”).
The formula for acceleration is:
Acceleration = (final velocity – starting velocity)
Time
Projectile motion is the motion of a thrown ball. The ball initially curves up or stays straight and then arcs back down to the
surface. This arcing motion is due to gravity pulling down and friction slowing it down.
Between point a and b the object is at a constant speed
Between points b and c the object is at rest
Between points c and d it is at a constant speed again.
Below are distance time graphs and what they represent.
Something at rest
constant speed
accelerating
Below are distance time graphs and what they represent.
Deceleration
accelerating
object is not moving
WAVES
A wave is a disturbance that transfers energy through matter or through space. Some waves, like sound waves, must travel
through matter while others, like light, can travel through space. Energy is transferred to nearby particles and they move, causing
other particles to move. Energy is transferred from one place to another. The particles of matter do NOT move along with the wave.
ONLY the energy that produces the wave moves with the wave.
Waves can be compressions of energy (Compression / longitudinal wave) or made up of up and down movements
(Transverse wave). An example of a compression wave is sound. Examples of transverse waves include water waves and earthquakes.
Parts of a Wave:
A. Amplitude - the height of a wave above or below the midline
B. Crest - the peak or top of the wave
C. Midline - original position of the medium before the waves move through it.
D. Trough - the lowest point of the wave
E. Wavelength - the distance between two peaks.
Relating Frequency and Wavelength
Frequency is the how fast the wave is moving. If you stand in one spot and watch a wave go by, it is the number of crests
that go by in a second.
A long wave (one that doesn’t have too many crests and has a long wavelength) has a low frequency.
A short wave (one that has a lot of crests or a short wavelength) has a high frequency.
The higher the frequency, the more energy a wave has. Also, waves with short wavelengths have more energy than larger
wavelengths.
The speed or velocity of a wave depends on the wavelength and the frequency. The formula for wave speed is:
Speed = wavelength x frequency
The electromagnetic spectrum is an order of electromagnetic waves in order of wavelength and frequency - a long
wavelength has a low frequency, a short wavelength has a high frequency. Electromagnetic waves can travel through space. They do
not need to travel through a medium like air or water, though they can.
The Spectrum in Order
Least E
Most E
Radio Waves
lowest frequency and longest wavelength, used for communication (radio and TV)
Microwaves
used in cooking and for RADAR
Infrared Waves
cannot be seen, felt as heat, “below” red, used for cooking, medicine, night sight
Visible Light
portion of the spectrum that your eye is sensitive to, consists of seven colors (ROYGBIV), red has the
lowest frequency/energy and violet has the highest frequency/energy
Ultraviolet Waves
present in sunlight, “beyond” violet, energy is enough to kill living cells, used for sterilization
X-Rays
energy is enough for photons to pass through the skin, for medicine
Gamma Rays
highest frequency, shortest wavelength, certain radioactive materials emit them, have tremendous
ability to penetrate matter, used in the treatment of cancer
WAVE INTERACTIONS
When a wave hits a piece of matter, the wave can be absorbed or it can be reflected.
Reflection
 the bouncing back after a wave strikes an object that does NOT absorb the wave’s energy.
 The Law of Reflection states that the angle of the incidence is equal to the angle of reflection. In other words, the angle that it
hits the object at will be the same angle, in the opposite direction, that the waves leaves the surface.
 There are three types of mirrors that reflect light. PLANE - flat surface, reflected image is the same size. CONCAVE - curves
inward, like the bowl of a spoon, reflected image is either enlarged (original image was close to the mirror ) or the reflected image
is smaller and upside-down (original image was far away). CONVEX - curves outward, like the back side of a spoon, reflected
image is always smaller and right side up, provide a wide angle of view so a large area can be seen.
 The reflection of sound is called an ECHO.
Refraction
 The bending of waves due to a change in speed. This time the wave is absorbed and not reflected.
 Waves move at different speeds in different types of matter. Temperature can also affect the speed of a wave.
 Examples include prisms (bends white light into its component colors), lenses like glasses and contacts, and a mirage.
Diffraction
 The bending of waves around a barrier. When it encounters a barrier, the wave can go around it.
 Electromagnetic waves, sound waves, and water waves can all be diffracted. Diffraction is important in the transfer of radio
waves. Longer AM wavelengths are easier to diffract than shorter FM wavelengths. That is why AM reception is often better
than FM reception around tall buildings and hills.
 Examples include rainbow glasses, diffraction gratings.
Interference
 The phenomenon which occurs when two waves meet while traveling along the same medium. The interference of waves
causes the medium to take on a shape which results from the net effect pf the two individual waves.
 When two waves’ crests or troughs combine, there is an additive effect – this is called constructive interference. When one
wave’s crest and another’s trough combine, there is a subtractive effect – this is called destructive interference.
Constructive interference
Destructive interference
SOUND
Sound moves from its source in the form of compression waves. Sound is a form of energy that causes the molecules of a
medium to vibrate back and forth. Sound cannot travel through space or a vacuum. Materials that can easily bounce back (elastic)
transmit sound easily. Solids are generally more elastic than liquids or gases because the molecules are not very far away and bounce
back quickly. Elasticity increases the speed of sound; If the objects are in the same phase (ex. both liquids), sound goes slower in the
denser medium. As temperature increases, the speed of sound increases. Sound travels faster at higher temperatures.
DOPPLER EFFECT
This is a common occurrence that depends on the frequency of sound (or light) waves. There is a change in pitch whenever
there is motion between the source of the sound (or light) and its receiver. Either the source of the sound or the receiver must move
relative to the other. Consider an ambulance siren moving towards you. Each time the siren sends out a new wave, the ambulance
moves ahead in the same direction as the wave. This gives shorter wavelengths and higher frequencies because the waves get pushed
together. So, the pitch goes up. As the ambulance passes you, it is traveling in the opposite direction and the waves spread out.
Wavelength gets longer, frequency gets lower, and the pitch goes down. This also happens with light when light from a star is being
sent back to earth. If the star is moving away relative to the earth, the light gets shifted to the red, called a red shift.
High pitch…closer to
him
Lower pitch…going
away from him
ELECTRICITY AND MAGNETISM
METHODS OF GENERATING ELECTRICITY
Electricity is a form of energy called electrical energy. It is basically moving electrons. It can be produced in several ways.
1. Static Electricity - This is a buildup of electrical charge when electrons are exchanged from one object to another. Once they
move to another object, they remain on that object. Static electricity is a result of friction. Friction separates electrons from the
surface of an object whose atoms hold electrons loosely. Some good ways to generate static electricity are to rub opposite
substances together like silk and glass or plastic and wool.
2. Electric Current - This is a streams of electrons that flow through a conductor, like a wire. An electric current can be produced
chemically, by moving water (hydroelectric), by solar cells (using sunlight), by wind, and by nuclear radiation (fission reaction).
A. Chemical energy comes from a wet cell or a dry cell battery. It changes chemical energy into electrical energy. It is a
reaction that is produced as atoms within a substance exchange, transfer, or lend electrons to another atom within the
substance of the cell. An electric cell contains two electrodes, two different substances. In a wet cell, the electrodes are
put in an electrolyte (liquid that can carry an electric current). The electrodes react with the electrolyte solution and
release electrons. Electrons move from the negative electrode to the positive electrode through a wire. A dry cell works
that same way except there is a solid paste, like ammonium chloride instead of the liquid electrolyte.
B. Hydroelectric power, nuclear energy and wind energy are generated through electromagnetism. The moving air or
water turns a turbine. A generator uses electromagnetic induction. Electromagnetic induction is the process of inducing
an electric current by moving a magnetic field through a wire coil without touching it. This is how water produces
electricity. Moving water turns a turbine, which holds a magnet. This process causes an electric current to flow.
INSULATORS AND CONDUCTORS
Conductors are materials that are good for carrying an electric charge. Insulators keep an electric charge from flowing.
Good conductors of electricity include metals, water, electrolytes (solutions containing ions), and the human body. Good insulators
include nonmetals, rubber, plastic, and wood. Sometimes an insulator and a conductor are put together to keep electricity flowing in a
particular direction. A copper wire is coated in plastic to protect anyone from getting electrocuted when they touch the wire.
ELECTRICAL UNITS
There are three ways to measure electricity. They are current, voltage, and resistance.
1. Current: This is the rate at which electric current flows through a wire. It is the number of electrons that pass by a specific
point in a circuit in one second. The symbol for current is “I” and it is measured in amperes or amps (A).
2. Voltage: Electrons need energy to force the electrons through the wire. Voltage is the amount of energy available to move
the electrons. The higher the voltage, the more work the electrons can do. The symbol for voltage is “V” and it is measured
in volts (V).
3. Resistance: This is the measure of how difficult it is to move electrons through a circuit. It is the force opposing the flow of
electrons. Good conductors have a low resistance and poor conductors have a high resistance. Resistance depends on the
material it is made from and its length, thickness, and temperature. The symbol for resistance is “R” and it is measured in
ohms ().
Ohm’s Law relates current, resistance, and voltage:
Current = voltage  resistance
MAGNETISM
Magnetism is a universal force like gravity. A magnet always has two poles - north and south. Like poles repel each other
and opposite poles attract. There is a magnetic field around a magnet and the invisible lines of force run from one pole to the other.
A magnetic field can be produced using a current through a wire and a piece of metal that can be magnetized. Electricity and
magnetism are related. Electricity can produce a magnetic field and magnetism can produce an electric current.
ELECTROMAGNETISM
An electromagnet is a temporary magnet. As long as there is a current flowing, a magnetic field is present. A simple
electromagnet consists of a battery, copper wire, and an iron nail. The strength of the electromagnet depends on the number of turns
in the wire coil and the size of the iron core. The greater the number of turns, the stronger the magnetic field that is produced.
Magnets are used in electric motors. An electric motor is a device that produces a direct current. It contains an
electromagnet, a permanent magnet, and a commutator. The electromagnet is placed between the poles of the permanent magnet. The
poles repel and attract each other and the electromagnet spins. Electric energy is converted into mechanical energy. This is the
opposite of a generator.
Magnets are also used in television sets. The Non-plasma televisions all have a cathode ray that uses electrons and
fluorescent materials to produce images on a screen. An electromagnet changes the path of the beam of electrons which allows it to
sweep the television screen many times a second.
A transformer is a device that uses electromagnetic induction to change the voltage of a current. They are basically iron
cores with wires wrapped around them. There are transformers at the power plant, at power substations, and on the utility pole near
your house. The one near your house looks like a trash can on the utility pole.
A transformer works by stepping up or stepping down the voltage of electricity. More current in a wire means that more
energy is wasted due to resistance in the wire. Power companies want to limit the amount of energy wasted. When energy is
transmitted over a long distance, the voltage is raised and the current is lowered.
The step up transformer raises the voltage. For instance a power plant will step up the voltage from 20,000 volts to 250,000
volts to run the electricity through the long distance transmission lines. The primary coil has a certain number of turns with the wire.
If the secondary coil has twice as many turns as the primary coil, the voltage will be twice as much in the secondary coil.