Transcript Système Internationale SI Units

Système Internationale
SI Units
• SI is a system of measurement used in
science based on powers of 10.
• Units are given using a prefix + a base unit
Base Units:
Prefixes:
Length = meter (m)
Kilo- (K) 1,000
Mass = gram (g)
Hecto- (H) 100
Volume = cubic meter (m³) or liters (L)
Deka- (D) 10
Time = seconds (s)
Base unit- 1
Temperature scale = celsius
deci- (d) 0.1
centi- (c) 0.01
milli- (m) 0.001
To remember the prefixes…
•
•
•
•
•
•
•
King
Henry
Danced
By
Dirty
Cow
Manure
Conversion:
80cm= _________meters
80cm x 1m/100cm =
0.8 m
2000mm = ___________meters
2000mm x 1m/1000mm =
2m
2 Kg = __________-mg
2Kg x 1,000,000mg/1Kg =
2,000,000 mg
800mL = __________L
800mL x 1L/1,000mL =
0.8 L
7,500 cg = __________Kg
7,500 cg x 1Kg/100,000cg =
0.075 Kg
K H D b d c m
-You can also count how many times you are multiplying or
dividing by 10 and then move the decimal point as necessary
SI Practice Conversions
1)2,345 g = ______________Kg
1) 2.345 Kg
2)3,462 mL = _____________DL
2) 0.3462 DL
3) 6.2 Km = ______________dm
3) 62,000dm
4) 78 Hg = _______________Kg
4) 7.8 Kg
5) 0.001 KL=_____________L
5) 1L
6) 0.000005 Km= _________mm
6) 5mm
7) 520 cm = _____________m
7) 5.2m
8) 892.2 dm =____________Dm
8) 8.922 Dm
9) 1,236,000mm³=_________Km³
9) 1.236 Km³
10) 3.5 hours= ___________seconds
10)12,600 seconds
Elements, Compounds, and Mixtures
We can describe matter based on its physical and chemical properties, but how
do we organize it?
Pure substances- any form of matter made of uniform particles
Mixture- matter made of multiple types of particles that are not chemically bound
Pure substances are split into two categories…
Elements- pure substance made up of only one type of atom
-cannot be broken down into simpler substances by physical or chemical
means
Compounds- pure substance made up of multiple types of atoms, chemically bound
to form particles called molecules
Elements are all made up of different types of atoms and organized according to
their physical and chemical properties on the periodic table.
Compounds
Compounds are made of chemically bound elements, but their properties
can be different than the properties of the elements that make them.
dangerous elements can make harmless compounds and vice versa
A type of molecule is always made up of the same ratio of its component elements
Examples- water is always 2 Hydrogen atoms and 1 oxygen
-table salt is always 1 sodium atom and 1 chlorine atom
Compounds can be broken down during a chemical change.
-Sometimes they need a catalyst, sometimes they need an input of
energy, and sometimes they just degrade over time.
Eat a steak, its proteins are broken down into amino acids (mechanical and
chemical digestion) then your body reassembles the amino acids into other
proteins (translation).
Can you come up with any other examples of compound breaking down or
being formed?
Glucose
Deoxyribonucleic acid
How do we know when a chemical change has taken place?
Often the appearance (texture, color, physical state) can
change. Other signs of change include…
-heat
-odor
-fizzing and foaming
-sound
-light
Unlike physical changes, chemical changes are hard to reverse
-You can undo some reactions by chemical means, but most of the time
it is difficult
Atoms: Theory and Structure- Review
Atoms are the smallest unit of an element
Each element is made-up of a different type of atom, distinguished by the
number of the different subatomic particles that compose them.
There are three subatomic particles that make-up an atom
Proton: + charge and large mass (1amu)
Neutron: 0 charge and large mass (1amu)
Electron: - charge and small mass
Protons and neutrons are found in the nucleus of the atom and electrons orbit
around it, in what is called the electron cloud.
Atomic Theory:
•All substances are made of atoms, which in turn are made of smaller particles
called electrons, protons, and neutrons.
•They can be divided or combined (difficultly)- nuclear fusion and fission
•Atoms of the same element will all have the same number of protons and
electrons, but the number of neutrons and as a result the mass may vary (isotopes).
•Atoms do join with other atoms to form new substances (compounds)
Chemical Reactions
Chemical reactions (chemical changes) occur when compounds form or
degrade.
This occurs as a result of chemical bonding, when electrons are shared,
gained, or lost during the association of one atom with another
Do all of an atom’s electrons take part in chemical bonding?
No, usually only the valence electrons take part in chemical bonding
Valence electrons are the electrons on the outermost energy level
-an atom can have between 1 and 8 of them
-atoms bond with other atoms, gaining, losing, or sharing electrons, to get a
complete set of 8.
Which groups of elements want to lose electrons?
Which groups of elements want to gain electrons?
Which groups will most likely share their electrons?
There are different types of chemical bonds. The type depends on whether
electrons are transferred or shared between atoms.
Ionic Bonding
A type of bonding in which electrons are transferred from one atom to
another
Atoms are usually neutrally charged, having an equal number of + protons and –
electrons, but during an ionic bond that number is no longer equal.
In one of the bonding atoms, the number of electrons is greater than the
number of protons.
-they are negatively charged
In the other bonding atom, the number of electrons is less than the number
of protons.
-they are positively charged
Charged atoms are called ions
-positively charged ions are called cations
-negatively charged ions are called anions
Does an ionic compound, made of one cation
and one anion, have a charge?
No, the atoms in the compound are now
charged, but the compound itself is neutral
Ionic compounds bond together in rigid, geometric structures or chrystals.
-the actual shape in which they form is called a chrystal lattice
Identify the cation and anion in each of these ionic compounds
CaCl2
Ba
K2S
FeBr3
Cr2O3
KI
NaCl
FeO
KF
FrBr
Usually when an atom has more than one or two electrons to gain or lose it cannot
transfer its electrons.
In these cases they will share electrons, forming covalent bonds
Compounds formed of covalent bonds are called molecules
-a molecule is the simplest form of a covalent pure substance
Organic compounds (anything containing carbon) are all covalent.
-glucose
-starch
-celullose
You can diagram a molecule using an electron-dot diagram or Lewis structure.
Drawing an electron-dot diagram…
1) Write the element symbol of the largest atom
2) Draw dots around it representing its number of valence electrons
1) Try to space them evenly in groups of two
3) Place the other atoms around it in a way that allows each atom
to have 8 valence electrons (2 for hydrogen).
-A pair of electrons involved in a bond can be represented using a bar.
(single bond)
-4 electrons involved in a double bond can be represented using a double
bar (double bond)
-6 by a triple bar (triple bond)
Other types of Chemical Bonding
There are two other types of chemical bonding, metallic and hydrogen bonding
They do not result in new compounds like ionic and covalent bonding. Instead
they associate or hold like atoms together.
Metals are usually very dense, meaning that their atoms are very close
together. As a result their electron clouds overlap and their valence
electrons are allowed to move throughout the substance.
Hydrogen, because it is so simple an atom, when it binds with
electronegative atoms (want to take electrons) becomes slightly positive.
It will then associate with electronegative atoms of other molecules, limiting
how far apart the different molecules can go without more energy.
Metallic bonding gives metals some unique properties, such as electrical
conductivity, ductility, and malleability.
Electrical conductivity- since the valence electrons can move freely
through metals, an electric current (moving electrons) can also.
Ductility- ability to be drawn into wire
Malleability- ability to be hammered into sheets
Basically, metal can be bent into any shape necessary and can be used
to direct electricity.
As a result of hydrogen bonding, water molecules
tend to stick together.
This gives water molecules several unique
properties…adhesion, cohesion, and surface tension
Adhesion- water molecule’s tendency to stick to other objects
Cohesion- water molecule’s tendency to stick to each other
Surface tension- water molecule’s tendency to form a rigid
surface at the top of a liquid
These properties explain capillary action
Signs of Chemical Reactions
Chemical reactions often give us physical evidence that a reaction is taking place.
Such as…
Color change
Precipitate formation (forming a solid)
Gas release (creating a gas)
Heat (energy release)
Compounds are represented using chemical formulas (e.g. H2O) and chemical
reactions are represented using chemical equations.
6 CO2 + 6H2O
C6H12O6 + 6O2
Chemical equations tell you the chemical formulas of all of the compounds
involved and how many of each compound is involved.
We know…
-the number of each compound
-The kinds of atoms involved
-the number of each kind of atom
The compounds entering the reaction are called reactants
The compounds produced in the reaction are called products
The one BIG rule
The atoms in the reactants much equal the atoms in the products
The Law of Conservation of Mass
-Mass (matter) is neither created nor destroyed during a normal chemical or
physical reaction
As a result the atoms present before a reaction must also be present after a
reaction
To balance equations and make sure that no matter is lost or created, we use
coefficients.
-they tell us how many of a particular compound is involved in a reaction
-By adding them to one, two, or all of the compounds involved in a reaction
we can be sure that the same number of atoms enter and leave a reaction.
CO2
+
H2O
C6H12O6
+
O2
6CO2
+
6H2O
C6H12O6
+
6O2
Balancing chemical equations is part of a branch of chemistry called
Stoichiometry
Energy
Energy is the ability/potential to do work (move matter).
When matter interacts energy is transferred back and forth.
Something with a lot of energy could do a lot of work
Or
To do a lot of work (moving something massive), it requires a lot of energy
Energy in Chemical Reactions
Iron reacts with oxygen to form rust. How come your car doesn’t spontaneously rust
and fall apart?
Plants bond carbon dioxide and water to make glucose, why can they not do this
without light?
How come, after you remove the initial flame from a candle, it continues to burn?
The answer is energy
energy is transferred, released, or absorbed whenever chemical bonds form or break
This causes some reactions to take place very slowly, some to take place very quickly,
some to require a constant or initial input of energy, and some to release energy to the
environment.
Energy is absorbed when chemical bonds break and released when they form.
If a chemical reaction absorbs more energy breaking up its reactants than its
products release while being put together, then the reaction is called
endothermic.
-Endothermic- heat enters
-Endo- inside
Photosynthesis is an endothermic reaction
-the absorbed energy comes from the sun
If a chemical reactions releases more energy bonding its products than it
absorbs breaking its reactants, then the reaction is called exothermic.
-Exothermic- heat exits
-Exo- outside-exit
Cellular respiration is an exothermic reaction
-the energy released from breaking up glucose fuels our bodies
Some reactions will occur spontaneously without any initial input of energy, but
most of the time, even exothermic reactions need an initial input of energy to get
them started.
The amount of energy a reaction needs to get started is called activation energy
Exothermic reaction- heat energy
given off by products
Endothermic reaction- heat
energy stored by products
The speed at which reactants break and products form during a chemical reaction is
called its reaction rate.
Reaction rate is affected by how exposed the reactants are to each other
and the amount of ambient energy to start the reaction.
To speed up a reaction…
Increasing the temperature increases the amount of energy
Increasing the concentration of the reactants, the surface area on
which the can react, adding a catalyst, or removing an inhibitor
increases how exposed the reactants are to each other.
Catalyst- anything that lowers the activation energy
required to start and maintain a reaction
Inhibitor-anything that increases the activation energy
required to start or maintain a reaction.
-neither catalysts nor inhibitors are chemically
changed during a reaction
Color Quiz
1) Does a catalyst increase or decrease reaction rate?
Black- increase
orange-decrease
2) What is activation energy?
Black- energy needed to start a reaction
Orange- energy gained during a reaction
3) During an exothermic reaction, is the net energy gain positive or negative?
Black- positive
Orange- negative
4) During an exothermic reaction, the products …
Black- absorb heat
Orange- release heat
5) During an endothermic reaction, is more heat absorbed or released?
Black- released
Orange-absorbed
6) Photosynthesis is an example of what type of reaction?
Black-endothermic
Orange-exothermic
Energy associated with the motion and position of objects is called mechanical
energy. It is split into two types, kinetic energy and potential energy.
Kinetic energy is the energy of motion, describing how an object moves.
Potential energy is the energy of position, describing the potential an object has
to move as a result of its position in the universe.
Mechanical energy = Kinetic energy + Potential Energy
Kinetic energy depends on the mass of an object and how fast it is moving (its
velocity).
EK = (1/2)mv2
E = energy
K= type of energy
M= mass
V= velocity
Which value affects an objects kinetic energy more, mass or velocity? (p.241 practice)
Potential Energy comes in two forms, elastic potential and gravitational potential.
Elastic potential energy is an objects potential to spring back after being stressed
somehow.
e.g- stretching rubber band, drawing back a bow, compressing a spring
Gravitational potential energy is an objects potential to move as a result of gravity (to
fall). It depends on the height of an object and its weight (mass and force of gravity)
Eg = mgh
E= energy
G=type of energy
M= mass
P.242 practice
G= acceleration of gravity (9.8m/s²)
H= height
It can also be given as…
Gravitational potential energy = weight x height
When an object falls or an elastic is released, its potential energy is converted into
kinetic energy, but the total amount of energy stays the same.
When the ball hits the ground and stops
moving, its mechanical energy is gone.
Where did it go?
Energy that appears to be lost is really just transferred into a new form. There are seven
forms of energy…
1) Mechanical energy-energy associated with motion and position
2) Thermal energy- energy associated with heat (vibration of particles)
3) Chemical energy- energy stored in chemical bonds
We will talk in detail
about heat, light,
and sound later
4) Electrical energy- energy associated with moving electrons
5) Sound energy- energy of vibrating objects moving in waves through
matter
6) Light/radiant energy- energy moving through electromagnetic waves,
can travel outside matter
7) Nuclear energy- energy stored in the nucleus of an atom and released
during fission and fusion
Energy is converted from one form to another constantly and is involved in nearly
every event or occurrence in the universe
Example:
Mechanical energy of water (kinetic), transfers to a turbine that
converts mechanical energy into electric energy.
A light bulb then converts that electrical energy into radiant and
thermal energy that is transferred to the particles in the room
around the light.
Your eye receives the radiant energy and converts it back into
electric energy that travels through your optic nerve and to your
brain.
The purpose of a lot of the machines that humans use is to convert energy from
one form to another.
-the engine in a car converts chemical energy in gasoline into thermal
and kinetic energy.
Hydrotubine
Wind turbine
The Law of Conservation of Energy says that energy cannot be created or destroyed
-There is more energy in your food than you can use as fuel to move.
-There is more energy gasoline than your car can use to move.
No machine or natural energy conversion is 100% effective, though, so where
does the energy go?
Whenever an object moves, there is a force that pushes
in the opposite direction that resists its motion.
This force is called friction.
The energy wasted to overcome friction is converted into
thermal energy.
Thermal energy, waste energy, is released in every energy conversion.
How efficient a machine or process is depends on how much energy is wasted
overcoming friction.
The less thermal energy released during an energy conversion, the more efficient
it is.
The more energy efficient a process is, the less fuel it needs in the first place.
Energy Resources
Our energy resources on earth are split into two groups, renewable and nonrenewable.
Renewable resources can be regenerated or provide an unlimited supply of energy.
e.g. biomass (regenerated), wind, solar (unlimited supply)
Nonrenewable resources cannot be regenerated under reasonable means. There is a
finite supply of them on earth.
e.g. fossil fuels, uranium
-basically anything that comes from mining
Energy resource Advantages
Disadvantages
Fossil fuels
-High energy output
-Easy to access and transport
-Can be used to generate
electricity and produce synthetic
materials
-are nonrenewable
-produce smog
-can produce acid rain
-risk of spills
Nuclear
-concentrated form of energy
-no air pollution
-produces radioactive waste
-is nonrenewable
Solar
-limitless source of energy
-no pollution
-expensive to harness on large
scale
-only useful in sunny areas
Water
-is renewable
-does not produce air pollution
-requires dams, which distrupt
ecosystems
-only available near rivers
Wind
-is renewable
-relatively inexpensive
-does not produce air pollution
-only practical in windy areas
Geothermal
-almost limitless source of energy
-plants require little land
-only practical near hotspots
-produces waste water, which
pollutes soil
Biomass
-is renewable
-is inexpensive
-requires large areas of farmland
-produces smoke
Color Quiz
There is a limited supply of _______________ resources.
Red- renewable
Green- nonrenewable
Which is an example of a nonrenewable resource?
Red- wind
Green- fossil fuels
Which is an example of a renewable resource?
Red- solar
Green- uranium (nuclear)
Which force opposes all motion?
Red- friction
Green- gravity
A process that creates a lot of heat as a biproduct would be called energetically
__________________.
Red- efficient
Green- inefficient
The form of energy associated with the movement and position of objects is
______.
Red- mechanical energy
Green- chemical energy
The biggest downside to hydroelectricity is ________________.
Red- ecosystem damage
Green- air pollution
What is Temperature?
Temperature is the average of kinetic energy of the particles in an object or area.
It tells you on average, how fast the particles are moving (vibrating or bouncing
around).
-all particles are moving at different speeds and in different directions,
so the temperature of a whole object is just an average.
If something has a high temperature, its particles are moving quickly.
If something has a low temperature, its particles are moving slowly.
Think about state changes…
Which has a higher temperature
-solids or liquids?
-liquids or gases?
What changed to cause the solid to melt? The liquid to vaporize?
What is thermal expansion?
As objects increase in temperature and their particles move more, they spread out.
-the whole object swells as a result.
This is called thermal expansion
Thermal expansion allows thermometers to work…
It causes your doors to stick in the summer…
It causes hot air to rise (if volume increases and mass stays the same,
density decreases)…
Buildings built in places where the temperature changes a lot have to be
built with thermal expansion in mind.
How is temperature measured?
Temperature is measured on any of three scales, Fahrenheit, Celsius, or Kelvin.
Fahrenheit is used in the U.S, but not in science.
Celsius is used internationally and in science because it is based on the
freezing and boiling temperatures of water.
Kelvin is also used in science, but it is centered around absolute zero.
Absolute zero- temperature at which all particle energy motion
stops. Particles have zero kinetic energy.
-There are no negative values in the Kelvin scale, but there are in
the Celsius and Fahrenheit scales.
Converting from one scale to another…
F = 9/5 C + 32
C= 5/9 (F-32)
K= C + 273
0° C =
273° K =
32°F
What is the scientific meaning of the word…Heat?
Heat is the energy transferred between objects at different temperatures.
When an ice tray is placed in the freezer, heat is transferred from the water to
the air in the freezer. When the water loses enough heat (energy) it freezes.
Heat is always transferred from the higher temperature object to the lower
temperature object.
-to make something cooler, you take away heat, you don’t add
cold.
The greater the difference in temperature, the faster heat is
transferred.
-think of heat as rolling down hill, the greater the
difference in temperature the steeper the hill.
When an object is heated, the energy is transferred in the form of thermal energy.
An object’s thermal energy is the total kinetic energy of the particles in an object or
area
vs
Temperature, which is the average kinetic energy of the particles in an object or
area
Thermal energy depends on amount, temperature does not.
Whether heat is transferred between two objects depends on their temperatures
not their thermal energy.
Some objects increase in temperature faster than others.
How well they conduct thermal energy is called thermal conductivity.
-leather seats compared to cloth seats in a car.
Objects that conduct thermal energy well have a low specific heat.
Specific heat is the amount of energy needed to
raise the temperature of 1Kg of a material
1°Celsius or Kelvin.
Unlike temperature, heat cannot be measured.
It must be calculated.
Heat (joules) = (specific heat) (mass -Kg) (change in temperature- C° or K°)
Heat can transfer from one object to another in several different ways.
Radiation- the transfer of energy by electromagnetic waves (e.g. light,
infrared etc.)
-can transfer through empty space outside of matter
Conduction- the transfer of energy through direct contact of their particles
-the hot pavement conducts its energy into your bare feet.
Convection- the transfer of energy by moving currents of water or gas
-the cooling effect of wind or moving water
Materials that conduct thermal energy well (usually with a low specific heat) are
called conductors.
-they exchange heat quickly
-e.g. baking pan
Materials that do not conduct thermal energy well (usually with a high specific
heat) are called insulators.
-they do not exchange heat quickly
-e.g. oven mitt
Most of the energy on earth comes from the sun through radiation.
We can survive because the atmosphere lets some forms of electromagnetic
radiation through but not others.
It allows light through but blocks most ultraviolet light.
-damage to the ozone layer limits ability to do this
Greenhouse gases help keep that energy on earth and limit how much bounces
back out into space. They act as a thermal insulator.
-too few greenhouse gases and half of the planet would freeze over
each night.
-like wearing a t-shirt in January
-too many greenhouse gases and the earth will over heat
-like wearing a sweatshirt and jacket in August
Electromagnetic
Radiation and Sound
Waves
What are waves?
They are disturbances caused by the movement of energy, either through matter or
through empty space.
As a wave moves across the ocean, each water molecule only moves up and
down. They do not flow all the way to the shore.
As kinetic energy passes from one particle to the next, each particle performs
the same motion (like dominoes falling).
If you are floating in a boat on the ocean, do the waves carry you all the way to
shore?
No, the energy makes the boat go up and down, just like the water molecules,
and then it continues on.
What does a surfer have to do to catch a wave?
They have to paddle the same velocity as the wave of energy is moving until
it breaks and they can let gravity carry them (like sliding down a ramp that
keeps growing).
When energy is moving through matter, that matter is called a medium.
Waves that can only travel when in a medium are called mechanical waves.
e.g. sound waves, ocean waves, earthquake waves
Waves that do not need a medium to travel through are called electromagnetic waves.
They can travel through matter, but they can transmit energy without it.
e.g. light, microwaves, infrared,
ultraviolet, x-rays, gamma rays
Not all waves follow the same path.
Some vibrate perpendicular (a right angle) to the direction motion, called
transverse waves
-they can vibrate up and down or side to side.
-they look like traditional ocean waves.
-electromagnetic waves are all considered transverse waves, while only
some mechanical waves are transverse.
The highest point of a transverse wave is called the crest
And the lowest point is called a trough
When particles vibrate forward and backwards in the same direction as the wave is
moving, it is called a longitudinal wave.
-they are made as matter sequentially stretches and squeezes.
-stretching or spacing out particles is called rarefaction.
-squeezing particles together is called compression.
Sound waves are all longitudinal waves.
Waves are described by several key properties…
Amplitude, wavelength, frequency, and wave speed.
Amplitude- how high or far a particle vibrates from its rest position.
-High energy waves lead to greater amplitude
Wavelength (λ)- the distance between the crests or compressions of a wave.
-High energy waves have shorter wavelengths (waves are close
together).
Frequency (f)- number of waves in a given amount of time
-the unit used is usually hertz (1Hz = 1wave/second)
Wave speed (v)- the speed at which one wave travels.
v = (λ)(f)
If given two of the following, wavelength, wave speed, and frequency, you
can solve for the third.
What happens to waves when they collide with a new medium or with another wave?
When interacting with another medium, waves can reflect, refract, or diffract.
When multiple waves interact, we get interference.
When a wave hits an object that it cannot transmit through, it bounces back.
This bounce back is called reflection.
An echo is an example of a reflection.
The colors that you see are the wavelengths of light being reflected back.
-if you see black, all colors are being transmitted and non is being
reflected
-if you see white, all colors are being reflected and non is
transmitted.
A mirror reflects light without distorting it
Why do we see rainbows after a sun shower?
As light passes through the water particles in the air, it is bent. Different
wavelengths (colors) bend more than others, so they separate.
The bending of a wave as it passes from one medium to another is called
refraction.
As a wave passes through one medium to another, its wavelength and wave
speed can change, but its frequency stays the same.
How come we can hear around corners but can’t see?
Diffraction is a wave’s ability to bend around an obstacle.
Waves with long wavelengths diffract more than shorter wavelengths.
Light barely diffracts at all
High pitched sounds diffract well
Low pitched sounds diffract very well
What happens when two waves collide?
For the moment that they are passing through the same space, we have
something called interference.
If two troughs or crests coincide, they add together and appear as one big wave
-Constructive interference
If a crest passes the trough of another wave, they take away from each other
-Destructive interference
How do Noise Cancelling Headphones work?
When outgoing waves and reflecting waves interfere to create what look like
static waves (not moving), we say that they have produced standing waves.
The frequency at which standing waves are produced is called that
object’s resonating frequency.
When one object vibrates near the resonating frequency of another object, it can
make that other object start to vibrate as well.
Basically, one sound causes another object to start making a
sound
-This is called resonance
What is sound?
Sound is a longitudinal wave of energy created by the vibration (oscillation) of
matter that travels through a medium.
Anything that is vibrating creates a sound, as it compresses and
rarefacts the air particles around it.
-we can only hear only hear the sounds of waves from objects
vibrating at certain frequencies though.
As waves travel through the air and through our ear, they cause hair cells attached
to nerves to move, which sends signals to our brain.
Different hair cells react to different frequency sounds.
If they are damaged by high amplitude waves, we do not re-grow them.
Your hearing peaked the day that you were born.
How fast do sound waves travel?
The speed of sound waves depends on the medium they are traveling through.
The denser and warmer the medium the faster the waves will travel.
At high altitudes, where it is cold, sound travels slower than at room
temperature.
It travels faster through liquids and even faster through solids.
Mach 3 means 3x the speed of sound
If you put your ear to the ground, you
can hear a train coming well before
you could if you were standing.
Pitch, Frequency, Amplitude, and Volume
The pitch of a sound (how high or low) depends on the frequency of the waves.
-high frequency = high pitch
The volume of a sound (loudness) depends on the amplitude of the waves.
-high amplitude = loud
-adding energy to a wave increases its amplitude
-the loudness of a sound is measured in decibels
Sounds over 120 dB can physically hurt
How do bats use sound?
The reflection of sound is called an echo.
Bats (and whales) use echoes to find objects and navigate in a process called
echolocation.
-electronic echolocation is called sonar.
-an ultrasound is a procedure where sound waves beyond human
hearing are used to find objects inside the human body.
Sound waves experience interference constantly. It can be either constructive
or destructive.
Constructive interference makes sounds louder
Destructive interference makes sounds softer
As an object approaches the speed of sound, the waves get so close together
that constructive interference produces a wave with extremely high amplitude
called a shockwave.
The sound heard from a shockwave is called a sonic boom.
Most notes made by instruments are actually made up of several different waves
at different frequencies combining through constructive interference.
-the result is that note’s sound quality for that particular instrument.
When different frequency sounds from different instruments or voices work
together pleasantly, we say that they are in harmony.
When they do not, it is cacophony.
What are electromagnetic waves?
They are waves of energy, made of both electric and magnetic fields, that can
travel either through a medium or a vacuum.
What is an electric field?
The field energy associated with charged particles (usually moving electrons).
What is a magnetic field?
The field of energy associated with moving charged particles or inherently
polar materials.
So…when charged particles move, they have both an electric and a magnetic
field.
The two parts of an electromagnetic wave vibrate perpendicular to each other.
When charged particles vibrate they produce electromagnetic waves.
How fast do EM waves travel?
Like all waves, EM waves change speeds when they change mediums, but in
a vacuum (without a medium), they travel 300,000,000 m/s.
That is 186,000 miles per second
Or 7.5 times around the earth per second.
Nothing in the universe travels faster than light.
-It is considered a cosmic speed limit
There are theories regarding what would happen as you approached the speed of
sound that include things like time travel and exponential mass increase.
EM waves vary in wavelength and frequency.
The different types of EM waves (waves within a certain range frequency or
wavelength) are laid out in a spectrum according to their frequencies and
wavelengths.
Low frequency, long wavelengths are one side.
High frequency, short wavelengths are on the other.
In general, the shorter the wavelength/higher frequency the wave the more
dangerous it can be.
Radio waves- λ > 30cm- television and radio signals are carried by radio waves
Microwaves- 30cm>λ>1mm-used in microwaves, cell phones, and radar
Infrared waves- 1mm>λ> 700nm- most heat, especially from the sun, travels as
infrared waves
Visible light- 700nm>λ>400nm- all of the light and color that we see
Long λ
Short λ
Ultraviolet waves- 400nm>λ60nm- caused skin damage (mutates cell DNA) but
allows cells to produce vitamin D.
X-rays- 60nm>λ>0.001nm- travels through most materials, used to see inside
people, bags, etc.
Gamma rays-0.1nm>λ- travels through most materials, used to treat some cancers
The difference between x-rays and gamma rays is based more on source
than wavelength (usually different types of radioactive material)
EM waves, just like any other wave, can reflect, refract, and diffract.
Unless we are looking directly at a light source, any time we see an object, we
are actually seeing the light reflecting off of it.
When light bounces off a smooth surface (regular reflection) the different
waves are still arranged the same way, so the reflected light looks the
same as the source.
-Mirrors
When light bounces off of a rough surface (diffuse
reflection), the different waves are reflected in different
directions, so you just see a general mix of color.
-Walls
When the energy from an EM wave transfers to matter rather than being reflected
or transmitted, it has been absorbed.
-Most light sources emit a wide range of EM waves, the colors we see
are the ones that we not absorbed.
Walls and even the particles in the air reflect light and send it in all different
directions, this is called scattering.
-This is why you can see even if you are not directly in a beam of light.
Long wave length light diffracts better than short wavelength light, so it doesn’t
scatter as easily. That is why for most of the day, the sky is a short wavelength
color (blue).
Since light travels slower through air than it does through a vacuum, and slower
through water than it does through air, when it hits these new mediums at an angle it
bends.
This is refraction.
Short wavelength light refracts more than long wavelength light.
-so violets and blues bend a lot and red bends little.
This separation of colors creates rainbows.
Since EM waves have such short wavelengths, they do not diffract well, but they
do diffract.
This is why the edge of a shadow (penumbra) is fuzzy and lunar
eclipses make the moon look red.
Interference of light can take place, resulting in brighter or dimmer light, but it is hard to
notice unless working with a light of only one wavelength (one color).
Why do we see the colors that we do?
We see whatever wavelengths (colors) reach our eyes, which is determined
by how materials, absorb, transmit, and reflect light.
Objects that transmit all colors without scattering them are transparent.
Objects that transmit colors but scatter them are translucent.
Objects that do not transmit visual light are opaque.
With opaque objects, we see whatever light is reflected.
Transparent and translucent objects appear to be whatever color they are
transmitting.
-a sprite bottle looks green because it transmits mostly green light and
absorbs the rest.
A pigment is any material/chemical that controls how a substance interacts with light
and gives it its color.
How do we see color?
There is a difference between primary colors and primary pigments.
-primary colors are the wavelengths of light that can combine to produce a full
spectrum of colors (produce white light).
-primary pigments are the pigments/colors needed to make pigments that absorb
all the different wavelengths of light (produces black pigment).
-mixing paints is mixing pigments.
Primary colors- green, blue, and red
Primary pigments- cyan, yellow, magenta
Electricity and Magnetism
What is electric energy?
How are charged particles different than neutral particles?
Charged particles follow the law of electric charges, which states that like
particles with like charges repel and opposite charges attract.
The force, whether attractive or repulsive, that one particle puts on another is its
electric force.
The area in which this force works is that particle’s electric field.
Individual atoms and most compounds, in the natural state, are neutral (have the same
number of electrons and protons).
If electrons are lost or gained, a substance becomes electrically charged.
If objects rub together (friction) they can pass electrons and become charged.
If a charged material touches an uncharged material it can pass on electrons
(conduction).
If a charged material goes near an uncharged material its electric force can cause
the electrons in the uncharged material to shift and create a charged area
(induction).
Electrons move to try to balance the charge of the system
that they are involved in. They are not created or
destroyed. They are conserved.
Electrons will keep moving until they contact a positively charged substance.
Substances that allow the free movement of electrons are called conductors
e.g. metal (wires)
Substances that limit the movement of electrons are called insulators
e.g. rubber (wire coating)
Compounds held together by ionic or metallic bonds usually conduct
electricity well. Covalent compounds do not.
How much a substance opposes the flow of electrons is called its resistance.
What is static electricity?
Static electricity is an electric charge when electrons are not moving from one object to
another.
The clothes in the dryer rub together, build-up a charge. When they stop
moving, they stop passing electrons.
They now stick together because of static electricity (+ sock sticks to – shirt)
Objects don’t hold on to static electricity forever, eventually
the built-up electrons will find some place to go. This is
called electric discharge.
Electric discharge could be small and unnoticeable or large, loud, and bright.
Electrons could pass harmlessly to particles in the air.
Electrons could jump from your hand to a friend or door knob.
Electrons could jump from cloud to cloud or from a cloud to the
ground (lighting).
As clouds move and build, they pass electrons and a static charge can build-up.
When these charges jump from a negative cloud to a positive cloud or from a
negative cloud to the positive ground we see and hear lightning.
I hope no one ever feels it.
Color Quiz
• Electricity is a build-up of which type of particles.
– Blue- charged
Red- neutral
• Particles with the same charge…
– Blue- attract
Red-repel
• Electric charges can be built-up through
conduction, friction, or …
– Blue- induction
Red- radiation
• The measure of how a substance allows
electricity to pass through it is…
– Blue-insulation
Red- resistance
• Static electricity is different than current
electricity because the charged particles…
– Blue- do not move
Red- do move
How can we describe the movement of electrons?
Electric current- The rate at which electrons move passed a certain point.
Measured in amperes (amps)
-Individual electrons don’t usually move very fast, but they will all start to
move as soon as that option is made available, so your lights turn on quickly.
When a current flows in only one direction it is called a direct
current (DC). Current in batteries.
When a current alternates which direction it flows it is called an
alternating current (AC). Current moving through the wires in your
house.
-The direction alternates
because the charge at the source
(turbine at the power station) changes
Another way to describe electricity is voltage.
Voltage describes the gradient between the positive and the negative charges.
The larger the gradient, the more energy the electric current will carry and the
faster its electrons will move.
The batteries in a remote control have a voltage of 1.5.
The current running through your house is 120 V.
Lightning varies but can be 100,000,000 V.
Static electricity can’t do work. A current has to be present, which means that there
can’t be a point in the system where electrons get stopped.
A complete system or path through which electrons can flow
without stopping is called a circuit.
When you flip the switch on the wall, you complete the circuit and
allow the current to flow.
When you flip it again you break the circuit and stop the flow of
electricity.
There are two main types of circuits, series circuits and parallel circuits.
Series circuits are simple, single loops. Electrons all follow one path.
-like cars going around a race track.
Parallel circuits are more complex loops. Electrons have multiple paths that
they could follow.
-like roads around a city
If a series circuit is broken any device (load) running on that current will stop
functioning.
If a parallel circuit breaks, one or two loads may be cut off, but electrons can
find their way to the others.
Your house is one large parallel circuit
Series circuit
Parallel circuit
Electric currents can carry a lot of energy and be dangerous.
What can you do to promote electrical safety?
What is a magnet?
A magnet is anything that attracts iron (they work with other metals too, but iron
is the most common).
Magnetic materials have constantly moving electrons, the moving electric fields
create magnetic force, the attractive or repulsive ability of a magnet.
-All atoms have moving electrons, but in magnets they move in a way
so that their respective magnetic fields add to each other rather than cancel
each other out.
Magnets also always have poles, opposite sides of the
object that have opposite magnetic forces.
The poles of a magnet are labeled by how they interact with the magnetic field
surrounding earth.
-The north pole on a magnet orients itself towards the north pole.
-The south pole on a magnet orients itself towards the south pole.
-The North Pole on earth actually has the opposite charge as the north
pole of a magnet.
A compass is just a magnet allowed to spin freely.
What is an electromagnet?
Since an electric current is comprised of moving electrons it has a magnetic field.
Electromagnets wrap coils carrying an electric current into a tight bundle called a
solenoid that increases the strength of the magnetic field.
-the more moving electrons that can be squeezed into an area, stronger
its magnetic field will be.
This interaction between electricity and magnetism is called electromagnetism.
Describe some ways electricity is used productively in your life?
What things can you do to ensure that the electricity around you is safe?
Since we see light that is reflected not absorbed, our eyes are adapted to
recognize the primary colors, red, green, and blue.
We have cones in the back of our eyes that send signals through the optic
nerve to our brain.
Each cone is adapted to receive either red, green, or blue light.
If someone is color blind, or color deficient, one or more of these cones does not
function properly.
It is an x-linked recessive disorder, which means the genes controlling the proteins
inside these cones is on the X chromosome.
It is expressed most frequently in men and is inherited from the mother’s side of
the family.
What kind of technology have people developed to work with light (help us see)?