Transcript What is Mechanical Energy?

The Law of Conservation of
Energy
• Energy cannot be created or destroyed; it
may be transformed from one form into
another, but the total amount of energy
never changes.
What is energy?
• “the ability to do work”
• The combination of energy and matter
make up the universe:
– Matter is substance, and energy is the
mover of substance.
Energy is
nature’s way of keeping score.
We sense energy only
when the score
changes,
either a transformation
from one form of
energy to another,
or a transfer of energy
from one point to
another.
How is all energy divided?
All Energy
Potential
Energy
Gravitation
Potential
Energy
Elastic
Potential
Energy
Kinetic
Energy
Chemical
Potential
Energy
Potential
• energy of position
or energy in
storage.
– Water behind a dam
– Hammer over head
– Food on the plate
Kinetic
• energy of motion,
the form capable of
doing work
– Flowing water
– A falling hammer
– Electrons regenerating
ATP in a bio’l cell
PE = mgh
• m = mass (kg)
• h = height (m)
• g = accel due to
gravity
– (9.8 m/s2)
Kinetic Energy
• KE of an object depends
upon two variables:
1. the mass (m) of the
object
2.the speed (v) of the
object.
What is Gravitational Potential
Energy?
o Potential energy
due to an object’s
position
Don’t look down,
Rover!
Good boy!
o P.E. = mass x
height x gravity
Gravitational Potential Energy
• GPE is the energy stored in
an object as the result of
its vertical position (i.e., height).
• Amount of GPE is dependent
on two variables:
1.the mass
2.the height
Calculating Gravitational
Potential Energy
(rate an object falls
due to gravity) g =
9.8m/sec2
What is Potential Energy?
o Energy that is stored
and waiting to be
used later
What is Elastic Potential Energy?
o Potential energy due compression or
expansion of an elastic object.
Notice the ball compressing
and expanding
What is Chemical Potential Energy?
o Potential energy
stored within the
chemical bonds of
an object
What is Kinetic Energy?
o Energy an object has due
to its motion
o K.E. = .5(mass x speed2)
KE = 1/2 m v2
•
•
•
•
4 kg bowling ball
at 10 m/s
= .5 (4kg) (10m/s)2
= 200 J
•
•
•
•
.25 kg baseball
at 50 m/s
= .5 (.25kg) (50 m/s)2
= 312 J
The greater the mass or velocity of a moving object, the more kinetic energy it
has.
Courtesy Jerry Ohlinger’s Movie Material Store
Work is done when a force is exerted over a distance.
Work
• is equal to the force that is exerted times
the distance over which it is exerted.
• W=Fxd
• The unit of work combines the unit of
force (N) with the unit of distance (m)
• Newton-meter (N-m) aka Joule.
You carry a 20 kg suitcase upstairs, a
distance of 4m. How much work did you
do?
• W=Fxd
• F = ma
• = (20 kg) (10m/s2) = 200 N
• W=Fxd
• = (200 N) (4m)
• = 800 J
Power
• measures the rate of work done.
• or the rate at which energy is
expended.
• Power is the amount of work done,
divided by the time it takes to do it.
• Power (watts) = work (joules) / time
(sec)
• P = W/t
Power
• Since work performed equals energy
expended,
• Power (watts) = energy (joules) / time
(sec)
• The watt is defined as the expenditure of
1 joule of energy in 1 second.
(75 watt light bulb consumes 75 J/sec)
Important formulas and units
Quantity
Force
Work
Energy
Power
Definition
mass x accel.
force x distance
power x time
work / time
Units
newtons
joules
joules
watts
Ex. Problem on Power:
• Your CD system, uses 250 watts of
electrical power.
• You play it for 3 hrs. How much energy
used? About how much would it cost? If
one kWh is $.08.
• Energy (J) = power (watts) x time (sec) =
(250w) (3hr) = 750 Whr = .75 kWh
• The cost = 8 cents/ kWh x .75 kWh
• = 6 cents
Power = work / time
• . Two physics students, Will N. Andable
and Ben Pumpiniron, are in the
weightlifting room. Will lifts the 100-pound
barbell over his head 10 times in one
minute; Ben lifts the 100-pound barbell
over his head 10 times in 10 seconds.
Which student does the most work? Which
student delivers the most power?
Mechanical Advantage
• The number of times a machine multiplies
your effort force.
– Example: If you push on the handle of a car
jack with a force of 30 lbs and the jack lifts a
3000 lb car, what is the jack’s mechanical
advantage?
– The jack multiplies your effort force by 100
times.
There are 2 types of mechanical advantage.
• IMA – Ideal mechanical
advantage.
• This is the number of
times a machine is
designed to multiply your
effort force.
• It is based on
measurements of the
machine.
• Ignores friction
• AMA – Actual mechanical
advantage
• This is the number of
times the machine
actually multiplies your
effort force.
• AMA = resistance
force/effort force.
• Includes the effects of
friction
IMA is always greater than AMA.
Mechanical Advantage
• Mechanical advantage is the ratio of output force
divided by input force. If the output force is bigger
than the input force, a machine has a mechanical
advantage greater than one.
• If a machine increases an input force of 10 pounds
to an output force of 100 pounds, the machine has a
mechanical advantage (MA) of 10.
• In machines that increase distance instead of force,
the MA is the ratio of the output distance and input
distance.
MA = output/input
Drawing Conclusions
•
•
•
•
•
Two divers of equal mass about to dive
Diver A has > Potential Energy than B
Compare divers positions
Which diver will hit water @ highest speed
What happens to energy when diver
enters the water?
Diver A
Fastest
Diver B
6 fundamental forms of energy
1.
2.
3.
4.
5.
6.
mechanical energy
Thermal (heat) energy
electromagnetic energy
electrical energy
nuclear energy
chemical energy
What is the source of our
energy?
• The source of
practically all
our energy is
the Sun.
What is Mechanical Energy?
o Energy due to a
object’s motion
(kinetic) or position
(potential).
The bowling ball has
mechanical energy.
When the ball strikes
the pins, mechanical
energy is transferred
to the pins!
Mechanical energy is the movement
of machine parts.
Mechanical energy comes from the motion (kinetic
energy) and position (potential energy) of objects.
EXAMPLES:
Wind-up toys, grandfather clocks,
and pogo sticks
Wind power uses mechanical energy
to help create electricity.
Potential energy + Kinetic energy = Mechanical energy
Examples of Mechanical Energy
What is Electromagnetic
Energy?
o Light energy
o Includes energy from
gamma rays, xrays,
ultraviolet rays,
visible light, infrared
rays, microwave and
radio bands
What is Electrical Energy?
o Energy caused by
the movement of
electrons
o Easily transported
through power lines
and converted into
other forms of
energy
Electrical energy is the movement
of electrons.
Examples:
Lightning and static electricity
occur naturally.
Science hasn't found a way to use
natural forms of electrical energy.
We use different energy sources to
create electrical energy by using
generators and turbines.
What is Chemical Energy?
o Energy that is
available for release
from chemical
reactions.
The chemical bonds in
a matchstick store
energy that is
transformed into
thermal energy when
the match is struck.
Examples of Chemical Energy
Chemical energy is the energy
stored in the bonds of atoms and
molecules. This a form of potential
energy until the bonds are broken.
Examples:
Fossil fuels store chemical energy.
Products that contain chemical
energy include: TNT, baking soda,
and a match. Biomass, petroleum,
natural gas, propane and coal are
examples of stored chemical energy.
What is Thermal Energy?
o
Heat energy
o The heat energy of an
object determines how
active its atoms are.
A hot object is one whose atoms
and molecules are excited
and show rapid movement.
A cooler object's molecules and
atoms will show less
movement.
Thermal energy is the internal energy in
substances - the vibration and movement
of atoms and molecules within substance.
Thermal energy is created in the
movement of atoms.
EXAMPLES:
Boiling water, burning wood, and
rubbing your hands together really fast.
Geothermal and passive solar are
sources of heat energy.
Nuclear energy is the energy stored in the
nucleus of an atom.
Nuclear energy is unusual in that it can
give off energy in the form of light or
heat, but it is the change in the atom's
makeup that produces the energy.
All power plants convert heat into electricity using steam. At nuclear power
plants, the heat to make the steam is created when atoms split- fission.
Fission takes place when the nucleus of a heavy atom like plutonium or
uranium is split into two when struck by a neutron. This releases more
neutrons which repeat the process and releases more nuclear energy (heat).
This heat boils water and creates steam that turns a turbine. As a turbine
spins, the generator turns and its magnetic field produces electricity that goes
to your house.
QUIZ TIME!
What type of energy
cooks food in a
microwave oven?
ELECTROMAGNETIC
ENERGY
What type of energy is
the spinning plate
inside of a microwave
oven?
MECHANICAL ENERGY
QUIZ TIME!
Electrical energy is
transported to your house
through power lines.
When you plug an electric fan
to a power outlet, electrical
energy is transform into
what type of energy?
MECHANICAL ENERGY
QUIZ TIME!
What energy transformation
occurs when an electric lamp
is turned on?
ELECTRICAL ENERGY

ELECTROMAGNETIC ENERGY
What types of energy are shown below?
Mechanical and Thermal Energy
(Don’t forget friction)
What type of energy is shown below?
Chemical Energy
What types of energy are shown below?
Electrical, Mechanical and
Electromagnetic Energy
What type of energy is shown below?
Chemical Energy (yummy)
What type of energy is shown below?
Thermal Energy
What types of energy are shown below?
Mechanical, Electromagnetic,
Electrical, Chemical and Thermal
Energy
The Law of Conservation of
Energy
• Energy cannot be created or destroyed; it
may be transformed from one form into
another, but the total amount of energy
never changes.