Download Types and Forms of Energy Notes

Types and Forms of Energy:
2 Types:
1. Potential energy: the energy that an object has because of its position,
shape, or condition of the object
*Chemical energy is the energy stored in chemical bonds in molecules
Chemical energy is a form of potential energy
Food we eat is stored as chemical energy in our bodies
PE is sometimes called : Energy of position, because this energy results from the
position of objects
Example: an elastic band stretched between your fingers- once flung will exert a
lot of E on the object it hits
An elastic band that is not stretched exerts very little energy on an object
An apple falling from a tree, exerts a lot of E on the ground when it lands
Gravitational Potential Energy: depends on Mass of object AND
Height of object
PE = mgh m=mass g= force of gravity h = height of object
Force of gravity = 9.8m/s2 or round to 10m/s2
Mass times gravity = weight( a force)
2. Kinetic Energy – the energy of a moving object
KE depends on the mass of the object and its speed
KE =1/2 mv2 (onehalf mass times velocity squared
Conservation of Energy: PE = KE
If a object has a total E value of 100J and the object is at rest at some height; then
the KE of the object =0J
The PE of the object is 100J
Once the object drops and Lands, the object exerts 100J of energy onto the
ground and the PE value =0J
What about Heat, sound ,light Energy
If the object is moving through space, some E is lost as heat, some E is lost as
sound
If the object is moving from space through our atmosphere, some E is lost as light
(remember a meteor(“shooting star”)
3. Mechanical Energy: the amount of work an object can “do” because of the
object’s KE and the objects PE
a. Example: the apple falling ; as the apple falls the amount of PE and KE
is changing; PE will decrease and KE will increase until the apple hits
the ground and the KE will be 100% and the PE will be 0%
b. Suppose this apple lands on your head will it hurt more or less than if
the same apple landed on LeBron James’ head???
Remember work = movement of an object due to a force
6 Forms of Energy:
Mechanical, Thermal, Chemical, Nuclear, Electrical, and Radiant
4. Thermal energy aka HEAT
a. Kinetic theory – all atoms/molecules are always in motion
b. The average motion of these atoms/molecules = temperature
c. 3 ways heat is transferred
i. Conduction – objects must be in contact with each other;
hotter objects loses energy to cooler object
ii. Convection – density differences move the fluid; cold fluids
more dense than warm fluids;
iii. Radiation – no contact; electromagnetic radiation moves
through atmosphere and once in contact with object transfers
E to object – dark colors absorb more radiation than light
colors
d. Wind, solar, geothermal, hydro power all due to HEAT Energy
differences - Solar Energy creates different wind currents as land
heats up and water areas heat up – land heats up faster than water
5. Electrical Energy: (chapter 16)
OBJECTIVE:
Explain what factors affect the strength of the electric force
Describe the characteristics of the electric field due to a charge
a. Electric charge – an imbalance in the number of protons and
electrons
i. Negatively charged objects : #e > #p
ii. Positively charged objects : #p > #e
iii. Conductors – a material that allows charges to run freely –
metals are great conductors
iv. Insulators – a material that does not transfer current easily –
plastic
v. An electric cord – electrons move freely on the twisted copper
wires inside the cord through the outlet; the plastic cover on
the wire prevents an electric shock to you
vi. Protons and neutrons are FIXED in nucleus of atom – valence
electrons are easily transferred
vii. STATIC ELECTRICITY: a stationary(static) electric charge,
usually produced by friction EXAMPLE: walking across the
carpet, your feet slide against the carpet, pulling electrons off
of the carpet – add ing more electrons to your body – you
touch a door knob the door knob is neutral and the negative
charges move away from you, while the positive charges of
doorknob allow the movement of the negative charges from
you to go into door knob and exchange the electrons to door
knob – presenting you with a shock – the metal door knob is a
great conductor of all of your extra electrons!!
viii. Winter – dry air – not enough water vapor in air to take some
of these extra electrons off of you – so the static charge builds
up until you meet a great conductor!
ix. ELECTRIC FORCE: The force of attraction or repulsion between
objects due to charge: similar to the Force of Gravity which is
ONLY an attractive force
OBJECTIVE 16-2 CURRENT
1. Describe how batteries are sources of voltage
2. Explain how a potential difference(voltage) produces a
current in a conductor
3. Define resistance
4. Calculate the resistance, current or voltage
5. Distinguish between conductors, superconductors,
semiconductors, and insulators
x. CURRENT: the rate electric charges move through a conductor
– movement of matter(not energy)
1. SI unit for current = ampere “A”
2. Direct current = movement of current from one terminal
to the other – example – battery
b. The potential energy of a ball decreases as it moves downhill; the
electrical potential energy between 2 negative charges decreases as
the distance between them increases
c. Potential difference = voltage ; Volt is the unit for potential
difference; V
d. Voltage (potential difference) between 2 terminals of a battery
e.
voltage and "static electricity" go together.
Whenever a negative charge attracts a positive
charge, invisible fields of voltage must exist between
the charges. Voltage causes the attraction between
opposite charges; the voltage fields reach across
space. In reality, "static" electricity has nothing to do
with motion (or with being static.) Instead static
electricity involves high voltage. Scuff across a rug,
and you charge your body to several thousand volts.
When you remove a wool sock from your clothes
dryer, and all the fibers stand outwards, the fibers are
following the invisible lines of voltage in the air.
Fibers are the "iron filings" that make the voltage
patterns visibile
f.
Voltage and e-fields are basically the same thing: if efields are like the slope of a mountainside, then the
volts are like the various heights of each different
spot on the mountain.
When a flashlight turns on the lightbulb connects the terminals of the battery and
electrons move from high PE to low PE – the movement of electrons = CURRRENT
Resistance: the opposition created by a material to the flow
of current – ALLOW FOR DIFFERENT AMOUNT OF CURRENT
Why does a small wire have more resistance than a large
wire?
If we look at the cross sectional area of each wire, we
see that a thicker wire has greater area than a smaller
one.
In general, resistance is given by the following
equation:
R=l*p/A
where l is the length, p is the resistivity of the material
used, and A is the cross sectional area of the wire.
The larger A is, the smaller R becomes.
Why? A larger area will allow more current to flow past
a given point in a given amount of time. Think of traffic
on a highway as an analogy: 4 lanes moves much
faster than 1 lane since additional lanes allow more
room for the cars to travel. It's the same for electrons
moving through a wire; more space allows more to
travel.
120 VOLTS – common household
voltage
Different light bulbs 40W or 100 W
40 W has more resistance – allows less
current to flow – less light
The filament in the bulb is the source of
RESISTANCE
Resistance = voltage/current or
R=V/I
Or Voltage = Resistance X current or
V=R x I
SUPER CONDUCTORS – when some
metals and compounds have ZERO
resistance due to being super cooled
SEMICONDUCTORS – materials that in
their pure state usually act as insulators,
but with an added impurity(another
atom/molecule, can act as a conductor
– example – silicon chips in computers
g. The potential energy of a ball decreases as it moves downhill; the
electrical potential energy between 2 negative charges decreases as
the distance between them increases
h. Potential difference = voltage ; Volt is the unit for potential
difference; V
i. Voltage (potential difference) between 2 terminals of a battery
i. When a flashlight turns on the lightbulb connects the terminals
of the battery and electrons move from high PE to low PE – the
movement of electrons = CURRRENT
6. Circuits
Electric circuit = a set of electrical components connected such they provide
one or more complete paths for the movement of charges
When the battery is connected to a light bulb, the voltage across the
battery generates a current that lights the bulb
A switch can be used to open or close a circuit
Knife switch – metal bar that when touching both sides of the switch closes
the circuit allowing electrons to flow – light is turned on
When bar is up, not touching both sides of switch, circuit is open, no
flow of electrons – light is off
Magnetism and electric currents (17-2)
Objective: describe how magnetism is produced by electric currents
A current carrying wire creates a magnetic field
“right hand rule” – If you imagine holding a wire in your right hand with
your thumb pointing in the direction of the current the direction that your
fingers would curl in is the direction of the magnetic field
If you increase the current in the wire – you increase the size of the
magnetic field
NEVER HOLD A LIVE BARE WIRE
Solenoid – wrap a wire into a coil – the magnetic field of each LOOP of wire
adds to the strength of the magnetic field
Strength of solenoid depends on # of loops of wire and amount of current
Electromagnet – a current-carrying solenoid with an iron core – the
magnetic field of the solenoid causes the iron core to become a magnet;
the magnetic field of the iron rod adds to the coil’s magnetic field – creating
a STRONGER magnet
ELECTRIC MOTORS – a device that converts electrical energy into
mechanical energy – you
tubehttp://www.youtube.com/watch?v=d_aTC0iKO68
Electric motors use magnetic force to cause motion
The coil of wire in a motor turns when a current is in the wire
The coil in the electric motor keeps spinning
If the coil is attached to an axle, which is attached to a wheel or propeller,
WORK can be done!
Show electromagnetic induction brightstorm2
Electric motor – converts electrical current to mechanical force
Generator – converts mechanical force to electric current
Large power plants use generators to convert mechanical E to Electrical E
Combustion reactions create heat which is used to form steam to turn the
blades of a turbine, which are attached to a core wrapped with loops of
wire that rotate in a STRONG MAGNETIC FIELD  Electrical Energy