Transcript Energy – Part II

Forms of Energy – Part II
Forms of Energy
Mechanical
Electrical
Chemical
Nuclear
Thermal/Geotherm
al
Sound
Seismic
Radiant
Kinetic and Potential Energies
Combined
Mechanical Energy – The sum of potential energy and
kinetic energy in a system of objects.
The energy an object has because of a combination of
the following: 1. The movement of its parts (kinetic energy)
2. The position of its parts (potential energy)
Example: Opening a door
•Potential Energy – the energy stored in the person
•Kinetic Energy – lifting my hand to push the door
•Mechanical Energy – my PE and KE were transferred
into mechanical energy which caused
work to be done (the door opens).
Mechanical Energy
How could a bowling ball have mechanical
energy?
•PE – bowling ball has mass and the PE increases as you pull it
back.
•KE – release the bowling ball as it moves down the lane.
Because of its mechanical energy it is able to do work on the pins!
Can you give some examples of mechanical energy?
Thermal Energy
Thermal Energy – The sum of the kinetic energy and
potential energy of the particles that make up an
object
Cannot always be seen.
Individual particles vibrate back and forth in place,
giving them kinetic energy .
The particles also have potential energy because of
the distance between particles and the charge of
the particles.
Thermal Energy
As the water heats up to make a cup of coffee the
particles begin to increase kinetic energy (velocity of
particles) and increase potential energy (distance
between particles increases) resulting in an increase of
thermal energy.
Thermal Energy in the Earth
The particles in Earth’s interior contain great amounts of
thermal energy.
This type of energy is called geothermal energy
Hot rocks underground heat
water to produce steam.
We drill holes down to the hot
region, steam comes up, is
purified and used to drive
turbines, which drive electric
generators.
Geothermal Energy Advantages
Does not produce any pollution
Power stations do not take up much room, therefore
there is not much environmental impact
No fuel is needed
Once you've built a geothermal power station, the
energy is almost free. (It may need a little energy to
run a pump, but this can be taken from the energy
being generated. )
IF IT’S SO GREAT, WHY DON’T WE USE IT!?
•There aren’t many places you can build a power station
•You need specific rocks that can be drilled into and at a depth you
can drill down to.
Types of Kinetic Energy
At this point you know that anything in motion has
kinetic energy, including:
Large objects that you can see
Small particles that you cannot see (molecules, ions,
atoms, and electrons)
Electric Energy
Electric Energy – The energy caused by the movement
of electrons.
Can be easily transported through power lines and
transformed into other forms of energy.
Electrons move around the nucleus of an atom
and they can move from one atom to another.
When electrons move, they have kinetic energy and
create an electric current.
Types of Potential Energy
Potential energy – stored energy that depends on:
Position or shape of an object.
Chemical Energy
Chemical Energy – energy that is stored in and
released from the bonds between atoms.
Most electric energy (a type of kinetic) comes from
fossil fuels such as petroleum, natural gas, and
coal.
The atoms that make up fossil fuels are joined by
chemical bonds
Chemical Energy
When fossil fuels burn, the chemical bonds between
atoms that make up the fossil fuel break apart
.
When this happens,
thermal energy.
chemical energy transforms into
What are some other forms of
Chemical Energy?
The chemical energy in
food is released while the
food is being digested and
the molecules of food are
broken down into smaller
pieces. As the bonds
between the atoms of the
food break or loosen, new
substances are created as a
result of the chemical
reactions taking place.
Inside the battery, a reaction
between the chemicals takes
place. But reaction takes
place only if there is a flow
of electrons. Batteries can be
stored for a long time and
still work because the
chemical process doesn't
start until the electrons flow
from the negative to the
positive terminals through a
circuit.
Air activated hand warmers
contain various chemicals. As
the disposable packet is
opened, oxygen crosses the
permeable cover and reacts
with iron, in the presence of
catalyst salt and water. The
production of Fe2O3 is an
exothermic reaction, generating
heat typically between 1 and 10
hours.
Nuclear Energy
Nuclear Energy – energy stored in and released from the
nucleus of an atom.
Majority of energy on Earth comes from the Sun
Nuclear fusion and nuclear fission release nuclear
energy.
Nuclear Fusion – A process that occurs in the sun which joins
the nuclei of atoms and releases large
amounts of energy.
Nuclear Fission - Nuclear energy plants on Earth break apart
the nuclei of certain atoms.
Energy from Waves
Wave – a disturbance that carries energy from
one place to another.
Waves move energy , NOT matter.
WAVELENGTH
CREST
AMPLITUDE
TROUGH
Energy from Waves – Sound Energy
Sound Energy – the form of energy associated
with the vibration or disturbance of matter
Some animals emit sound waves to find their
prey.
For example:
Bats – the amount of time it takes sound
waves to travel to their prey and echo back
tells the bat the location of the prey it’s
hunting.
Energy from Waves
Seismic Energy – is the energy transferred by
waves moving through the ground.
Earthquake’s occur when Earth’s tectonic plates
suddenly shift position.
The kinetic energy of plate movement is carried
through the ground by seismic waves
Seismic Waves
Body waves – travel through interior of Earth. P (primary) waves
– fastest and first to arrive. S (secondary) wave
slower, and arrives after p wave.
Surface waves - travel through Earth’s crust – responsible for
damage associated with earthquakes.
How is Seismic Energy
Measured?
Seismograph – an instrument for measuring seismic waves
(earthquakes).
Consists of a frame and a mass that can move relative to it. When
the ground shakes, the frame vibrates as well while the mass tends
not to move due to inertia. The difference in movement between the
frame and the mass is amplified and recorded electronically.
Measure:
Magnitude: size of earthquake
Depth: how deep the earthquake is
Location: where the earthquake occurred.
Energy from Waves
Radiant Energy – the energy carried by electromagnetic waves.
Electromagnetic waves – electric force (example: shock you get when you
touch a metal doorknob) and magnetic force (example: the pull that
attracts metals to magnets) that move perpendicular to each other to
bring on an electric field around them.
Can travel through solids, liquids, gasses and vacuums.
There are several different kinds of electromagnetic waves – each with
different wavelengths, properties, frequencies and power. The entire
wave system is called” the electromagnetic spectrum.
Electromagnetic spectrum – the range of all possible
frequencies of electromagnetic radiation.
The relationship between energy and wavelength:
The shorter the wavelength the greater the
energy.
The longer the wavelength the weaker the
energy.
The wave with the highest frequency is: gamma rays
The wave with the lowest frequency is: radio rays
What’s the difference?
What is the difference between an energy TRANSFER
and an energy TRANSFORMATION?
Energy Transfer – When energy moves from one object to
another without changing its form
Energy Transformation - When one form of energy is
converted to another form of
energy.
Energy Transfers and
Transformations
In every energy transfer and transformation some
energy is transformed into thermal energy.
In every transformation such as electric to sound there
is always thermal energy being transferred to
surroundings.
Transfer or Transformation?
Transferred
Energy
1.A tennis racket
applies force to a
tennis ball when it
hits the ball, forcing
the ball to move
forward.
2.A softball player
throws a ball
toward first base.
3.Fuel in an engine
burns, and the car
moves forward.
4.A runner eats an
energy bar and
later that day runs
in the100-m race.
Transformed
Energy
Type(s) of Energy
Being Transferred
or Transformed
Transfer or Transformation?
5.Lights glow in the
night sky when the
power switch is
turned on.
6.A hockey stick
stops
a sliding puck and
sends it toward the
goal.
7.A truck roars by a
row of apartments
on a quiet evening.
8.A song plays on
the
radio.
Plants and The Body
Plants carry out a process called
photosynthesis
How is photosynthesis an energy
transformation?
Plants use radiant energy (light from
Sun) to transform water and CO2
into Sugar and Oxygen. Sugar is
used as food for the plant and the
oxygen is released into the air we
breathe.
Types of Kinetic
Types of Potential
Both Kinetic and Potential
Energy and Work
Work – the transfer of energy that occurs when a force
makes an object move in the direction of the force.
Force- push or pull on an object
For example: The student does work on the drums when
he lifts them. Once the drums are in place, no work is
being done.
With your partners at
your table you have 1
minute to come up
with 3 examples of
work using this
definition.
What’s Work?
1. A scientist delivers a speech to an audience of his
peers. NO
2. A body builder lifts 350 pounds above his head. YES
3. A mother carries her baby from room to room. NO
4. A father pushes a baby in a carriage. YES
5. A woman carries a 20 kg grocery bag to her car? NO
Lets take a closer look at #3 and #5. Think about the definition – why are these
two examples NOT considered work?
#3 – the force is applied upward to hold the baby, however the baby moves in a horizontal
position with its mother. Therefore the mother is NOT doing work upon the baby.
#5 – the force is applied upward to the grocery bag, however the grocery bag moves in a
horizontal position with the woman. Therefore the woman is NOT doing work on the bag
Work
Work is done only while the force is moving
the object (in the direction that the force is
being applied).
Work also depends on:The distance an object moves
during the time the force is
applied.
Joules – the unit of energy and work
*Named After: James Prescott Joule – conducted
experiments measuring the amount of work needed to
create a given amount of heat.
Calculating Work
Work = Force x distance
Abbreviation Unit
Work
W
J (Joules) = 1kg x m2/s2
Force
F
N (Newtons) = 1kg x m/s2
Distance d
m (meters) = m
Sample Problem 1
A student lifts a bag from the floor to his shoulder 1.2 meters
above the floor, using a force of 50N. How much work does the
student do on the bag?
Sample Problem 2
Nicole lifts a flower pot onto a shelf 3 meters high, using a force of
30N. How much work is done to place the flower pot onto the shelf?
POWER
Power is the rate at which work is done.
Power = Work/Time
The unit of power is the watt.
Watt – equivalent to 1 Joule (work) per second (time)
Check for Understanding
1.Two physics students, Ben and Bonnie, are in
the weightlifting room. Bonnie lifts the 50 kg
barbell over her head (approximately .60 m) 10
times in one minute; Ben lifts the 50 kg barbell
the same distance over his head 10 times in 10
seconds.
Which student does the most work?
Which student delivers the most
Explain your answers.
power?
•
•
Ben and Bonnie do the
same amount of work; they
apply the same force to lift
the same barbell the same
distance above their
heads.
Yet, Ben is the most
powerful since he does the
same work in less time.
Power and time are
inversely proportional.
2. How much power will it take to move a 10 kg mass at an
acceleration of 2 m/s2 a distance of 10 meters in 5
seconds? This problem requires you to use the
formulas for force, work, and power all in the correct
order.
Force=Mass x Acceleration
Work=Force x Distance
Power = Work/Time
2. How much power will it take to move a 10 kg mass at an acceleration
of 2 m/s2 a distance of 10 meters in 5 seconds? This problem
requires you to use the formulas for force, work, and power all in
the correct order.
Force=Mass x Acceleration
Force=10 x 2
Force=20 N
Work=Force x Distance
Work = 20 x 10
Work = 200 Joules
Power = Work/Time
Power = 200/5
Power = 40 watts
Energy and Heat
In every energy transformation and every energy transfer, some
energy is transformed into thermal energy.
Thermal energy – the sum of kinetic and potential energy of the
particles that make up an object. (Example: Friction)
When thermal energy is moving from a region of higher
temperature to a region of lower temperature it is called heat.
Scientists sometimes call this heat waste energy
it is not easily used to do useful work.
because
Machines
Machines transfer mechanical energy
Simple Machines – machines that do work using
one movement.
Simple machines do not change the amount of
work required to do a task; they only change
the way work is done
Simple Machines
Inclined plane- a flat, sloped surface that makes it easier to
move an object from a lower to a higher elevation..
Screw – a modified version of an inclined plane. The
threads of the screw are a type of circular ramp (inclined
plane)
Simple Machines
Wedge – a modified inclined plane. Used to separate or
hold devices.
Lever – a simple machine that pivots around a fixed point
(fulcrum).
Simple Machines
Wheel and Axle – a shaft attached to a wheel of a larger diameter
so that both rotate together.
Pulley – a grooved wheel with a rope or cable wrapped around it.
Machines and Work
The work you do on a machine is called the
input work.
The work the machine does on an object is the
output work.
Machines make work easier by changing the distance
the object moves or the force required to do
work on an object
*remember – work is the product of force and distance.
Complex Machines
Complex Machines – two or more simple
machines working together.
Efficiency
Efficiency - the ratio of output work to input work.
Efficiency is a measure of how much work
put into the machine is changed into
useful output work
We express efficiency by using a percentage.
Efficiency equation:
𝑒𝑓𝑓𝑖𝑐𝑖𝑒𝑛𝑐𝑦 𝑖𝑛 % =
𝑒𝑓𝑓𝑖𝑐𝑖𝑒𝑛𝑐𝑦 =
𝑜𝑢𝑡𝑝𝑢𝑡 𝑤𝑜𝑟𝑘 (𝑖𝑛 𝐽)
𝑖𝑛𝑝𝑢𝑡 𝑤𝑜𝑟𝑘 (𝑖𝑛 𝐽)
𝑊 𝑜𝑢𝑡𝑝𝑢𝑡
𝑊 𝑖𝑛𝑝𝑢𝑡
x 100
x 100
Efficiency
The efficiency of a machine is NEVER 100%
Some work is always transformed into wasted thermal energy
because of friction
How could we improve efficiency of a machine?
Reduce the wasted thermal energy by reducing friction. We could
reduce friction by oiling the different parts of the machine.
A light bulb uses 120 J of electrical energy and produces 48 J of light
energy. Calculate the percent efficiency of the light bulb.
𝑒𝑓𝑓𝑖𝑐𝑖𝑒𝑛𝑐𝑦 =
𝑊 𝑜𝑢𝑡
𝑊 𝑖𝑛
x 100
Calculate the percent efficiency of an electric motor that uses 15,000 J
of energy to produce 11,500 J of useful energy
𝑒𝑓𝑓𝑖𝑐𝑖𝑒𝑛𝑐𝑦 =
𝑊 𝑜𝑢𝑡
𝑊 𝑖𝑛
x 100
Calculate the percent efficiency of an incandescent light bulb that
produces 2,500 J of light energy from 50,000 J of electrical energy.
𝑒𝑓𝑓𝑖𝑐𝑖𝑒𝑛𝑐𝑦 =
𝑊 𝑜𝑢𝑡
𝑊 𝑖𝑛
x 100
Practice Questions
1. Explain who is doing more work and why: a bricklayer
carrying bricks and placing them on the wall of a building being
constructed, or a project supervisor observing and recording the
progress of the workers from an observation booth.
2. How much work is done in pushing an object 7.0 m across a
floor with a force of 50 N and then pushing it back to its original
position? How much power is used if this work is done in 20
sec?
3. Using a single fixed pulley, how heavy a load could you lift?
Practice Questions
4. Give an example of a machine in which friction is both an
advantage and a disadvantage.
5. Why is it not possible to have a machine with 100% efficiency?
6. What is effort force? What is work input? Explain the
relationship between effort force, effort distance, and work
input.
Practice Questions
1. Explain who is doing more work and why: a bricklayer carrying bricks
and placing them on the wall of a building being constructed, or a project
supervisor observing and recording the progress of the workers from an
observation booth. Work is defined as a force applied to an object, moving
that object a distance in the direction of the applied force. The bricklayer is
doing more work.
2. How much work is done in pushing an object 7.0 m across a floor with a
force of 50 N and then pushing it back to its original position? How much
power is used if this work is done in 20 sec? Work = 7 m X 50 N X 2 = 700
N-m or J; Power = 700 N-m/20 sec = 35 W
3. Using a single fixed pulley, how heavy a load could you lift?Since a
fixed pulley has a mechanical advantage of one, it will only change the
direction of the force applied to it. You would be able to lift a load equal to
your own weight, minus the negative effects of friction.
Practice Questions
4. Give an example of a machine in which friction is both an advantage and
a disadvantage. One answer might be the use of a car jack. Advantage
of friction: It allows a car to be raised to a desired height without slipping.
Disadvantage of friction: It reduces efficiency.
5. Why is it not possible to have a machine with 100% efficiency? Friction
lowers the efficiency of a machine. Work output is always less than work
input, so an actual machine cannot be 100% efficient.
6. What is effort force? What is work input? Explain the relationship between
effort force, effort distance, and work input. The effort force is the force
applied to a machine. Work input is the work done on a machine. The
work input of a machine is equal to the effort force times the distance
over which the effort force is exerted.
Newton’s Laws and Simple
Machines
Recall and define each of Newton’s Laws of Motion
1st Law – an object in motion will stay in motion and an object
at rest will stay at rest unless acted on by an unbalanced force.
2nd Law – the acceleration of an object is equal to the object’s net
force divided by the objects mass.
3rd Law – every action has an equal and opposite reaction.
How could we relate these laws to machines?
Newton’s 1st Law and
Machines
Newton’s 1st Law tells us that the motion of an object changes
when the forces that act on the object are unbalanced.
When you pull a hammer handle, the claws of the hammer apply
a force on the nail. The hammer is acting as an unbalanced force
that causes the nail to go from rest to motion
.
Newton’s
nd
2
Law of Motion
Newton’s 2nd Law gives us the relationship between force, mass and
acceleration
Again, using the hammer as a lever applies to Newton’s 2nd Law
because the more force you apply to the hammer to remove the
nail the quicker the nail will move (accelerate) out of the piece of
wood.
Newton’s
rd
3
Law of Motion
Newton’s 3rd Law says that if one object applies a force on a second
object, the second object will apply an equal force in the opposite
direction.
For example, when you have a hammer being used as a lever to
pull out a nail, you apply force on the hammer. The hammer applies
an equal force in the opposite direction (back on you).
This is an action-reaction force