Download WORK… - science8wamogo

HAPPY MONDAY!
•You do NOT need your folders.
•If you finished Chapter 4 notes, have them
on your desk.
•Copy down tonight’s homework.
Today, we will…
•Preview week
•Finish talking about energy
•Talk about the concept of WORK
Monday
In class: Lecture notes on energy and work
HW: Finish Notes Chapter 4
Tuesday
In class: Lecture notes on work and machines
HW: Notes on Chapter 5 due on Thursday
Wednesday
In class: Lab stations on simple machines
HW: Finish Notes Chapter 5
Thursday
In class: Lecture notes on bridges
HW: Review earth science content in Grade 6 Jeopardy game
Friday
In class: Play Grade 6 Jeopardy
HW: Review life science content in Grade 7 Jeopardy game
2/23
States of Energy
• Energy can be in either of two states:
– Potential
– Kinetic
Kinetic Energy
• The energy of motion is called kinetic energy.
KE = ½ mv2
• Kinetic energy depends on both mass and
velocity.
• The faster an object moves, the more kinetic
energy it has.
• So, if an object is not moving, it has NO kinetic
energy.
• The greater the mass of a moving object, the
more kinetic energy it has.
Potential Energy
• Energy that is stored is called potential energy.
Potential Energy
ELASTIC POTENTIAL ENERGY (EPE)
– energy stored in compressed
springs, stretched rubber bands
CHEMICAL POTENTIAL ENERGY (CPE)
- energy stored in batteries, food, fuel
Gravitational potential energy
Gravitational Potential Energy
• Energy that is stored when an object is above the
ground and could fall is gravitational potential
energy (GPE)
• GPE depends on the weight of the object and how
high it is off the ground.
• Heavier objects have more GPE than light ones.
• The higher an object is, the more GPE is has.
Kinetic-Potential Energy Conversion
Roller coasters work because of the gravitational potential
energy that is built up when the cars are pulled mechanically
up the tallest hill. From that point, the conversion between
potential and kinetic energy powers the cars throughout the
entire ride.
Kinetic vs. Potential Energy
At the point of maximum potential energy, the
car has minimum kinetic energy, and vice versa.
As one increases, the other decreases.
Kinetic-Potential Energy Conversions
• As the basketball is
thrown into the air
and gravity brings it
back down, what
energy conversions
occur?
Ball speeds up
Ball slows down
KE is increasing
KE is decreasing
PE is decreasing
PE is increasing
Law of Conservation of Energy:
Energy cannot be created or destroyed, but
it can be changed from one form to another.
This means that, if you see a form of energy
that wasn’t there before, it must have
come from a form of energy that was
already there.
Like this!
WORK…
What is it, and why do we have to keep
doing it????
To a scientist,
work is the transfer of ENERGY that
occurs when a force makes an object
move.
Work is done on an object only when a
FORCE is being applied to the object
and the object moves in the same
direction as the force.
___ Mr. Fischer pushes the coffee cart down the hall.
___ Mr. Ranft lifts his new book about Godzilla up onto
his bookshelf.
___ While holding a University of Wisconsin “Bucky
Badger” statue, Ms. Pearce walks across the room.
___ Although she pushes as hard as she can, Mrs.
Stolle can’t move the snack machine by the cafeteria.
___ Mrs. Hanecak stays up all night to grade some
English essays.
Formula for calculating work:
work = force  distance
The SI unit for work is the JOULE (which is
also the SI unit for energy) because work is
the transfer of ENERGY.
A person used 500 N of force to move a full
wheelbarrow 30 meters. How much work
was done on the wheelbarrow?
A weightlifter lifts a 1,250 N barbell 2
meters. How much work was done on the
barbell?
A construction worker holding a 50 N brick
walks 10 meters. How much work was
done on the brick?
Before you leave…
•How does a scientist define work?
•What has to be true about the motion of an
object for work to be accomplished?
•Give an example in which force is exerted
on an object, but no work is done.