Download Energy guided reading

Name:________________________________ Period:____________
4.2 Energy and the Conservation of Energy Part 1 (pg. 83-87)
Energy
Defining
Energy
________________ is one of the fundamental quantities in our universe.
Without energy, _______________ could ever change. Yet energy itself
__________________ be directly smelled, _________________, touched, seen,
or _________________. Energy appears in many forms, such as
_____________ and _____________. Energy can travel in different ways,
such as in ______________ and _____________ waves and in electricity.
The workings of the ___________________________ (including all of our
man-made technology) can be viewed from the
_________________________ of energy flowing from one place to
_____________________ and changing back and forth from one ___________
to another.
Energy is a ______________ that measures the ability to cause
_____________. Energy can cause changes in temperature, ____________,
position, momentum, _________________, or other physical variables.
Energy can also ______________ change in materials, such as
__________________ wood changing into ashes and smoke.
Energy is a quantity that ____________________ the ability to
cause ______________ in a physical system.
Examples
Units of
Energy

A gust of wind has ______________ because it can move objects
in its path.
 A piece of ______________ in a fireplace has energy because it
can ________________ heat and light.
 You have energy because you can _______________ the motion
of your own body.
 Batteries have energy because they can be used in a radio to
make _________________
 ______________________ has energy because it can be
______________ in an engine to move a car.
 A ball at the top of a hill has energy because it can ___________
down the hill and ____________ objects in its path.
The unit of measurement
for energy is the
______________. One joule is
the ______________ needed to
push with a force of 1
_____________ over a distance
of 1 meter. The joule can be
abbreviated as _____ or as
Newton-meter (Nm),
which means 1 newton
multiplied by 1 meter. If you ___________ a pen with a force of 1
newton for a distance of 1 ________________ across a table, 1 joule of
Work means
different
things
What work
means in
physics
Work is done
on objects
your _____________ is converted into the energy of the pen’s motion.
The word work is used in many _______________________ ways.
 You should always _______________ over your work before
handing in a test.
 You _____ to work.
 Your toaster doesn’t ___________.
 You work with other ____________________ on a group project.
In physics, work has a very specific meaning. Work is the
_______________ of energy that results from applying a force over a
distance. To calculate work, you _______________ the force by the
distance the object moves in the direction of the _________________. If
you lift a block with a weight of 1 newton for a distance of 1
____________, you do 1 joule of work. One _____________ of energy is
transferred from your ___________ to the block, changing the block’s
energy. Both work and ______________ are measured in the same
units because work is a form of __________________.
When thinking about work, you should _________________ be clear
about which force is doing the work on which __________________.
Work is done ______ objects. If you lift a block 1 meter with a force
of 1 ________________, you have done 1 joule of work on the
______________.
Stop here and wait for further
instructions from Mrs. Nipper
Looking For….
Givens…
Work
Force and
Distance
Equation….
Units for
answer…
F=W÷d
M (meters)
Practice Problems for Work
1) Angel uses 20N of force to push a lawn mower 10 meters. How much work
does she do?
2) Sean uses 45N of force to stop the cart 1 meter from running his foot over.
How much work does he do?
3) Aaron does 15 Joules of work to push the pencil over 1 meter. How much
force did he use?
4) Desaree uses a force of 25 Newtons to lift her grocery bag while doing 50
Joules of work. How far did she lift the grocery bags?
5) The baseball player does 1234 Joules of work when hitting a baseball into left
field. Assuming the baseball landed 100 meters away from home plate, how
much force did the player use to hit the ball?
Potential Energy
What is
Potential
Energy?
Gravitational
Potential
Energy
How to
calculate
potential
energy
______________________ energy is energy due to position. The word
potential means that something is _____________ of becoming
something else. Systems or objects with potential _______________
are able to exert forces by exchanging energy as they change. For
example, a _______________ spring will use this energy to move itself
and anything attached to it back to its ______________________ length.
A block above a ______________ has
potential energy. If released, the
force of _________________ moves
the block to a position of
________________ energy. The term
gravitational potential energy
describes the energy of an
________________ object. The term
is often shortened to just
“potential energy” because a
common type of potential
energy in ______________ problems
is gravitational. Unless otherwise stated, you can assume
“potential energy” means ______________________ potential energy.
How much potential ___________
does a raised block have? The
block’s potential energy is
exactly the ________________ of
work it can do as it goes down,
which is _____________ to the
amount of work done to lift it up
to its _________________. Work is
force ___________________ by
distance. The force is the weight
(mg) of the block in
____________________. The distance
the ______________ can move is its
height (h) in meters. Multiplying
the weight by the ________________
gives you the block’s potential
energy at any given height.
Stop here and wait for further
instructions from Mrs. Nipper
Solving for…
Potential Energy
(Ep)
Givens…
Gravity (10 m/s/s)
Mass
height
Equation…
Ep=m·g·h
Mass
M=Ep ÷ (g·h)
height
H= Ep ÷ (g·m)
Unit for answer…
J (joules)
If the roller coaster car in this picture has a weight (m·g) of 400 N, what is the
potential energy of the car at each point?
a. Ep=
b. Ep=
c.
Ep=
Practice Problems
1.
Determine the amount of potential energy of a 5.0-N book that is moved to three
different shelves on a bookcase. The height of each shelf is 1.0 m, 1.5 m, and 2.0 m.
(remember that g= 10 m/s/s)
a. H= 1.0 m
b.
H= 1.5 m
c.
H= 2.0 m
2. You are on in-line skates at the top of a small hill. Your potential energy is equal to
1,000 J. The last time you checked, your mass was 60.0 kg.
a. What is your weight in newtons? (remember: w = m·g)
b. What is the height of the hill?
3. A 37 N object is lifted to a height of 3 meters. What is the potential energy of this
object?
4. At what height is an object that has a mass of 50 kg, if its gravitational potential
energy is 9800 J?
Kinetic Energy
Kinetic Energy
is energy of
motion
Kinetic energy
can do work
Kinetic energy
depends on
mass and
speed
Objects that are _______________ also have the ability to cause change.
Energy of ____________ is called kinetic energy. A moving billiard
ball has kinetic ___________ because it can hit another billiard ball
and change its motion. Kinetic energy can also be __________________
to potential energy. The kinetic energy of a _____________________
tossed upward converts into __________________ energy as its height
increases.
The amount of kinetic energy an object has _______________ the
amount of work the object can do by _________________ force as it
stops. Consider a moving skateboard and rider. Suppose it takes a
force of _________ N applied over a distance of ______ meters to slow
the skateboard to a stop (v=0). The kinetic energy of the
skateboard and rider is ________ Joules since that is the amount of
_________ it takes to stop the skateboard: 500 N · 10 m = 5,000 J.
If you had started with __________ the mass—say two
skateboarders—you would have to do ____________ as much work to
stop them both. Kinetic energy __________________ with mass. If the
skateboard and rider are moving faster, it also takes more
___________ to bring them to a stop. This means kinetic energy also
increases with ____________. Kinetic energy is related to both an
object’s speed and its mass.
Hint: It might help to use
0.5 instead of ½, especially
in your calculator.
Kinetic energy
increases as
the square of
the speed
Kinetic energy _________________ as the square of the speed. This
means that if you go ______________ as fast, your energy increase by
_________ times (22=4). If your speed is three times as fast, your
energy is _______________ times bigger (32=_______). A car moving at a
speed of 100 km/h (62 mph) has four times the kinetic energy it
had when going 50 km/h (31 mph). At a speed of 150 km/h (93
mph), it has nine times as much energy as it did at 50 km/h. The
stopping _________________ of a car is proportional to its ______________
energy. A car going twice as fast has four times the kinetic energy
and needs ____________ times the stopping distance. This is why
driving at __________ speeds can be so dangerous.
Stop here and wait for further
instructions from Mrs. Nipper
Practice Problems
1. A 1.0 kg ball is thrown up into the air with an initial velocity of 30. m/s. How
much kinetic energy does the ball have?
2. What is the kinetic energy of a 2,000-kg boat moving at 5.0 m/s?
3. A car is moving with the velocity of 10 m/s and is having mass of 250 Kg.
Calculate its Kinetic energy?
4. A 55 kg man runs at a speed of 4 m/s. Find his kinetic energy.