Transcript Work and Energy

Work and Energy
Work
• Imagine: After a heavy snowstorm Ryan’s
car gets stuck in the snow. He asks you to
help him move it, and you agree to help.
You shovel snow away from the car and
try to push it backwards. Although you
both try as hard as you can, the car will
just not move. You and Ryan are both
exhausted and decide to give up.
• Question: Did you do any work?????
Work
• NO!!!!!!
• In physics, work is only done when an
object moves.
• Definition of work: when you put force on
an object and the object moves.
Work
• One more thing…
– In order for work to be done, the force has to
be applied in the same direction that the
object is moving
• Ex: picking up a box
Pushing a table across the room
If you just walk across the room with a
heavy box, you are not doing any work!!!!
Examples of Work (Yes or No)
• Alex pushes against the wall and becomes
exhausted
• Mia pushes her science book off the table
• Dennis carries a heavy tray full of food
across the room
• A rocket lifting off into space
• Sarah pushes her car down the road
because she ran out of gas
Work
Remember, if you apply a force
to an object, but the object
doesn’t move, then no work
has been done!!!!
Energy
• Whenever an object has the ability to do
work, it is called energy
• (whenever a force moves an object,
energy is present)
• Lots and lots of different kinds of energy
• BUT, ALL energy can be broken down in
two categories
Kinetic Energy
• Kinetic Energy: energy when things are in
motion
• Talk to your partner….
• Any examples of kinetic energy???
Kinetic Energy
Which do you think will have more kinetic
energy?
• A. Throwing a bowling ball with a speed of
5 m/s
• B. Throwing a tennis ball with a speed of
5 m/s
• Kinetic energy will INCREASE as an
object’s mass INCREASES
Kinetic Energy
• Which will have more kinetic energy?
A. Throwing a tennis ball with a speed of 5
m/s
B. Throwing a tennis ball with a speed of 10
m/s
Kinetic energy will INCREASE as velocity
INCREASES
Potential Energy
• Potential Energy: stored energy (energy
of objects NOT in motion)
• Talk to your partner….
• Any examples of potential energy???
Potential Energy
• Two types of potential energy:
• Elastic potential energy: the energy of
objects that can be stretched or
compressed (rubber bands)
• Gravitational Potential Energy: the energy
of objects right before they fall
Potential Energy
•
Which would have more energy?
A. A huge bolder teetering on the edge of a
cliff 100 meters off the ground
B. A small rock teetering on the edge of a
cliff 100 meters off the ground
Potential energy INCREASES as mass
INCREASES
Potential Energy
•
Which would have more energy?
A. A huge boulder teetering on the edge of
a cliff 10 meters off the ground?
B. A huge boulder teetering on the edge of
a cliff 100 meters off the ground?
Potential energy INCREASES as height
INCREASES