Transcript MotionandForcesCh4No..

Motion and Forces
Work and Energy
Chapter 4
Bell Work 2/22/11
Write each statement, then decide if the
statement is true or false, if false correct
it.
1. An object has acceleration if its velocity is
changing.
2. Force is measured in joules.
3. Gravity is a force.
How do you work?
1. Do you think you did more work
the first time you lifted the book
or the second time you lifted the
book?
2. What do you think work means?
Work is the use of force to move
an object.
Work is done by a force that acts in the same
direction as the motion of an object.
Work = Force • distance
applied force
part of force not
doing work
applied force
object
part of force
doing work
object
direction of motion
direction of motion
13.1
Work is the use of force to move an object.
SIMUALATION
Determine how much
work is done by lifting
weights of different
masses.
4.1 Vocab
Work - The use of force to move an object
over a distance.
Joule - The unit used to measure work; one
joule of work is done when a force of one
newton moves an object one meter.
Bell Work 2/19/10
1. What two factors do you need to know to
calculate how much work was done in
any situation?
2. If you push very hard on an object but it
does not move, have you done work?
Explain,
3. Tina lifted a box 3 m. She used a force of
25 N. How much work did Tina do on the
box? Show your work!
Bell Work 2/22/10
1. If you apply a force of one Newton to a
box as you push it for one meter. How
many joules of work have you done?
2. If you push a cart with a force of 50 N for 3
m, how much work will you do?
3. Give an example of work that you have
done. Name the object that was moved
and the distance over which it moved.
Vocab 4.2
Potential energy - Stored energy, or the energy
an object has due to its position.
Calculating potential energy
Gravitational Potential Energy = mass x
gravitational acceleration x height
GPE = mgh
(on earth g = 9.8 m/s2)
MGH Example 1: What is the gravitational
potential energy of a girl who has a mass
of 40 kg and is standing on the edge of a
diving board that is 5 m above the water?
MGH Example 2: An apple with a mass of 0.1
kg is attached to a branch of an apple tree
4 m from the ground. How much
gravitational potential energy does the
apple have?
Kinetic Energy - The energy of motion; a
moving object has the most kinetic energy
at the point where it moves the fastest.
Calculating Kinetic Energy
Kinetic energy = mass x velocity2
2
KE = 0.5 m (v2)
KE Example 1: What is the kinetic energy of a
girl who has a mass of 40 kg and a velocity
of 3 m/s?
KE Example 2: A truck with a mass of 6000
kg is traveling north on a highway at a
speed of 17 m/s. What is the kinetic energy
of the truck?
Mechanical energy - A combination of the
kinetic energy and potential energy an
object has.
Calculating mechanical energy
Mechanical Energy = Potential Energy +
Kinetic Energy
ME = PE + KE
ME Example: How much mechanical energy
does a skateboarder have that has a
potential energy of 200 joules due to his
position at the top of a hill and a kinetic
energy of 100 joules due to his motion?
Conservation of energy - A law stating that no
matter how energy is transferred or
transformed, all of the energy is still present
in one form or another.
1
Top of Ramp
At the top of the ramp, the skater’s
mechanical energy is equal to her
potential energy because she has no
velocity.
100%
PE
2
Halfway Down Ramp
As the skater goes down the ramp, she loses height
but gains speed. The potential energy she loses is
equal to the kinetic energy she gains.
50%
PE
50%
KE
3
Bottom of Ramp
As the skater speeds along the bottom of the ramp, all
of the potential energy has changed to kinetic energy.
Her mechanical energy remains unchanged.
100%
KE
Forms of Energy
Thermal energy – the energy an object has due
to the motion of its molecules
Chemical energy – the energy stored in
chemical bonds that hold chemical compounds
together.
Nuclear energy – the potential energy stored in
the nucleus of an atom
Electromagnetic energy – the energy
associated with electrical and magnetic
interactions
Bell Work – 2/23/10
1. When Roger kicks a football, the football gains
mechanical energy because Roger does ______ on
the football.
2. Yelena holds a 5 kg ball over her head at a height of
2 m. What is the GPE of the ball?
3. Quentin has a mass of 50 kg. When he rides his
scooter at a velocity of 3 m/s, what is his kinetic
energy?
4. What is the formula for mechanical energy?
Bell Work 2/24/10
1. What is the law of conservation of
energy?
2. Describe 3 different forms of energy.
Bell Work 2/25/10
Draw the following picture and label where
the greatest and least PE and KE would
be.
Science Fair
Find your 3 favorite projects and write
down the following information about
each
Title
1. Problem
2. Independent Variable (IV)
3. Dependent Variable (DV)
4. Summarize the experiment
Bell Work 2/26/10
1. What was your favorite
science fair project
yesterday?
2. Write 3 sentences explaining
the project and why it was
your favorite project.
Bell Work 3/1/10
Match the correct term to each definition –
write the definition and the term
Terms – mechanical energy, potential energy,
kinetic energy, work
1. Stored energy
2. The use of force to move an object a certain
distance
3. The energy of motion
Power can be calculated from work
and time
Power = work
time
The unit of power is always a Watt (W)
Calculating power from work
Example: An Antarctic explorer uses 6000 J
of work to pull his sled for 60 s. What
power does he need?
Calculating power from work
Example 2: If a conveyor belt uses 10 J to
move a piece of candy a distance of 3 m in
20 s, what is the conveyor belt’s power?
Calculating power from work
Example 3: An elevator uses a force of 1710
N to lift 3 people up 1 floor. Each floor is 4
m high. The elevator takes 8 s to lift the 3
people up 2 floors. What is the elevators
power?
Calculating power from Energy
Power = Energy
time
The unit for power is Watts (W)
Calculating power from Energy
Example 1: A light bulb used 600 J of energy
in 6 s. What is the power of the light bulb?
Calculating power from Energy
Example 2: A laptop computer uses 100 J
every 2 seconds. How much power is
needed to run the computer?
Calculating power from Energy
Example 3: The power needed to pump
blood through your body is about 1.1 W.
How much energy does your body use
when pumping blood for 10 seconds?
13.3
Power is the rate at which work is done.
Power can be calculated from work and time.
Power = Work
time
power
watt
horsepower
Power can be calculated from energy and time.
Power = Energy
time
Power is measured in watts (W) and sometimes
horsepower (hp).
CHAPTER
RESOURCES
SECTION
OUTLINE
Bell work 3/2/10
1. How is power related to work?
2. What do you need to know to
calculate how much energy a light
bulb uses?
3. Which takes more power: lighting a
50 W bulb, 75 W bulb, or 100 W
bulb?
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Practice state standardized tests
Bell Work 3/5/10
George is pushing a box across
the floor at an angle and the
box is moving only forward.
Does all of George’s force do
work on the box? Explain.
Bell Work 3/8/10
Get out the Power House Web Worksheet
from last week and make sure you have
the 4 questions on the front answered
Bell Work 3/9/10
1. Motion is a change in _______ over time
2. Jenna knows that a friend runs 100m in 8 s.
She could use this to calculate her friend’s
________
3. Elena is riding her bicycle. She begins
pedaling harder. Her ______ will increase.
4. Speed in a specific direction is ______
5. Acceleration measures a change in _____
6. Latitude and longitude measure _____
7. You need to know ______ and _____ to
measure speed
Article Review
Include the following in complete sentences
•
•
•
•
•
•
•
Title and author of article
Who the article involves
What happened in the article
Where the article took place
When the article was written
Why the article is important (2 sent.)
How it relates to science (2 sent.)
Bell Work 3/11/10
1. Mary has a mass of 60 kg. When she rides
her bike at a velocity of 4 m/s, what is his
kinetic energy? KE = 1/2mv2.
2.The total mechanical energy of an object is
1500 J. If the kinetic energy of the object is
750 J, then the potential energy of the object
is (ME = KE + PE)
3. Tyler applies a 150 N force for 15 s to slide a
box 20 m across the floor. What is Tyler’s
power? (P = W/t) (W = Fd)
Bell Work 3/12/10
1. Identify the action/reaction force pair
involved when you catch a ball.
2. Explain the difference between
balanced forces and action/reaction
forces.
3. A man pushes on a wall with a force
of 50 N. What are the size and the
direction of the force that the wall
exerts on the man?
Bell Work 3/15/10
1. What is your favorite type
of ride to go on?
2. What is your favorite roller
coaster and why?
Bell Work 3/16/10
1. What do you think the most
difficult part will be when building
your roller coaster? Why?
2. What information would you like
to find today in order to help you
with the building of your roller
coaster?
Bell Work 3/17/10
Happy St. Patrick’s Day! Try this trivia.
1. What colors are in the Ireland flag?
2. What is the capital city of Ireland?
3. How many leaves are on a lucky clover?
4. What did St. Patrick drive out of Ireland?
(snakes, a car, Leprechauns)
5. Where do you find a pot of gold?
6. What happens if you look away from a
Leprechaun?
Green, Orange, White
• The colors in the flag have meaning:
Green is for the North, orange is for the
South and white is the Peace that binds
them
Dublin, Ireland
• Dublin, Ireland is the third most visited
capital city in Europe.
Four
• 4. According to the Guiness Book of World
Records the most leaves ever found on a
clover is 14.
Snakes
• According to the legend, St. Patrick drove
all the snakes in Ireland out of the country
and into the sea.
At the end of a rainbow
• If you are looking
for a pot of gold
go to the end of a
rainbow and see
if a Leprechaun
has hidden one
there.
He Disappears
• If you are lucky
enough to find a
leprechaun don’t
take your eyes off of
him, if you do he will
disappear with his
pot of gold.
Bell Work 3/18/10
1. What is the formula for speed?
2. Calculate the speed of a car
traveling 300 meters in 20
seconds.
3. Calculate the speed of your
marble if it complete the 6 meter
track in 12 seconds.
Bell Work 3/19/10
Draw and label the eight phases
of the moon. Use the space
science book if you need help.