Transcript potential energy

Work, Energy & Power
What’s work?
• A scientist delivers a speech to an
audience of his peers.
• A body builder lifts 350 pounds above
his head.
• A mother carries her baby from room
to room.
• A father pushes a baby in a carriage.
• A woman carries a 20 kg grocery bag
to her car?
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What’s work?
• A scientist delivers a speech to an audience
of his peers.
– No
• A body builder lifts 350 pounds above his
head.
– Yes
• A mother carries her baby from room to
room.
– No
• A father pushes a baby in a carriage.
– Yes
• A woman carries a 20 km grocery bag to her
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Formula for work
Work = Force x Distance
• Force=Newtons (N)
• Distance=meters (m)
• Work=Newton-meters (N*m)
– 1 N*m=1 Joule (J)
• Work=Joules (J)
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Work=Force*Distance
• Calculate: If a man
pushes a concrete
block 10 meters
with a force of 20 N,
how much work has
he done?
• 200 joules
(W = 20N x 10m)
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Power
the rate at which work is
done
• Power = Work/Time
• Power=(force x distance)/time
• Units:
– Work=Joules (J)=Newtons*meters (N*m)
– Power=Watts = Joules/second
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Who Needs It??
ENERGY:
POTENTIAL &
• Potential energy
• Kinetic energy
– Stored up energy
or energy held in
readiness
– Energy of motion
– KE= ½ mv2
– PE=mgh
•
•
•
•
PE=Joules (J)
m=mass (kg)
g=free fall acceleration
h=height (m)
KINETIC
• KE=Joules (J)
• m=mass (kg)
• v=velocity (m/s)
(9.8 m/s2)
ENERGY: The ability to do
work & cause change
• POTENTIAL ENERGY
– Stored-up energy, or
energy held in readiness
– EXAMPLES:
• Elastic Potential Energy
– Like slingshot or bungee
cord
• Gravitational Potential Energy
– Like diver on diving board
or light bulb in off position
• KINETIC ENERGY
– Energy of motion
– EXAMPLES
• moving bicycle
• moving auto
• high jumper jumping
• runner
POTENTIAL ENERGY
Energy stored or held in readiness
Most potential
What is the relationship between
Kinetic & Potential Energy?
http://www.classzone.com/books/ml_science_share/vis_sim/
mem05_pg69_potential/mem05_pg69_potential.html
THE TRADE OFF Between
Potential & Kinetic Energy
KINETIC ENERGY
Energy of motion
TYPES OF ENERGY
• MECHANICAL
– Car, plane, wagon
• THERMAL
– Heat from moving molecules
– Inside all matter; furnace
• ELECTROMAGNETIC
– Visible light, microwaves, radio
waves
• CHEMICAL
– Batteries, matches,
body cells
• ELECTRICAL
– Lightning, power lines
• NUCLEAR
– Nuclear power plants,
atomic bomb, sun &
stars
FORCES & MOTION
• FORCE
– A Push or a Pull
• MOTION
– A Change of Position
or Location
FRICTION AS A FORCE
• Strength of friction depends
on:
– Types of surfaces involved
– How hard surfaces push
together
TYPES OF FRICTION
• SLIDING FRICTION
– 2 solid surfaces
– Strength depends on roughness of surfaces
• ROLLING FRICTION
– One solid rolls over the other
– Much easier to move object
• FLUID FRICTION
– Solid moving through a liquid or gas
– Less than sliding friction
GRAVITY AS A FORCE
• FREE FALL
– Object accelerates as it falls due to gravity
– Object accelerates at rate of 9.8 m/s 2
• Every second velocity increases by 9.8 meters per second
• @ 2 seconds velocity is 9.8m/s + 9.8m/s = 19.6 m/s
• @ 3 seconds velocity is 9.8m/s + 9.8m/s + 9.8m/s = 29.4 m/s
GRAVITY
AS A FORCE
• AIR RESISTANCE
– Type of fluid friction that opposes motion
• WEIGHT
– Measures force of gravity on object
– Weight = Mass X Acceleration due to Gravity
WHAT MAKES OBJECTS
START MOVING . . .
STOP MOVING . . .
SLOW DOWN . . .
SPEED UP . . .
or CHANGE DIRECTION?
NEWTON’S FIRST LAW
• An object at rest remains at
rest and an object in motion
remains in motion unless acted
upon by an outside force.
NEWTON’S SECOND LAW
• THE FORCE EXERTED BY AN OBJECT IS
RELATED TO ITS MASS & ITS
ACCELERATION
• AN OBJECTS ACCELERATION IS
RELATED TO ITS MASS & THE FORCE
REQUIRED TO MOVE IT
• FORCE = MASS X ACCELERATION
WHAT AFFECTS WHAT?
FORCE = MASS X ACCELERATION
FORCE
ACCELERATION
MASS
MASS
ACCELERATION
FORCE
FORCE
ACCELERATION
NEWTON’S
THIRD LAW
• For every action, there
is an equal &
opposite reaction
THE END