Transcript Energy, work, Power ppt

UNIT 7
Energy & Work
Energy
• Energy – the ability to do work
• (the ability to cause a change)
Mechanical Energy
• Two types of mechanical energy
• Potential Energy - energy of position
• Kinetic energy – energy of motion
Kinetic Energy
• Kinetic energy – energy of motion
Kinetic energy
• What if the mass is doubled?
• What happens to the kinetic energy if the velocity is
doubled?
Potential Energy
• Potential energy – energy of
position/location
• Chemical potential
• Elastic potential
• Gravitational potential
• Electric potential
• Nuclear potential
Gravitational Potential Energy
Pe
Gravitational Potential Energy
• What happens to the gravitational potential energy if the
mass is doubled?
• What if the height is doubled?
Conservation of Energy
Law of Conservation of Energy
Energy cannot be created or destroyed. It can be
transformed from one form to another, but the total
amount of energy never changes.
Pendulum
Starts out not moving
Energy
Starts out not moving
Potential
Kinetic
Energy
Potential
Kinetic
Energy
Potential
Kinetic
Energy
Potential
Kinetic
Energy
Potential
Kinetic
Energy
Potential
Kinetic
Kinetic
Potential
Kinetic
Potential
Kinetic
Energy
Energy
Potential
Energy
Energy
Energy
Total energy = kinetic + potential
Potential
Kinetic
Potential
Kinetic
Total energy of the pendulum is conserved
Conservation of Energy
Law of Conservation of Energy
Energy cannot be created or destroyed. It can be
transformed from one form to another, but the total
amount of energy never changes.
- What are some examples of transformation of energy?
Different starting conditions
Energy
Energy
• What if I start the pendulum higher?
Potential
Kinetic
Potential
Kinetic
Different starting conditions
Energy
Energy
• What if I start the pendulum higher?
Potential
Kinetic
Potential
Kinetic
Different starting conditions
Energy
• What if I push the pendulum instead of just
letting go of it?
Potential
Kinetic
Different starting conditions
Energy
• What if I push the pendulum instead of just
letting go of it?
Potential
Kinetic
Rollercoaster
What would the energy
bar chart look like?
Energy
Potential
Kinetic
What would the energy
bar chart look like?
Energy
Potential
Kinetic
What would the energy
bar chart look like?
Energy
Potential
Kinetic
When does a pendulum have
the most Total Energy ?
Energy
• Energy initial = Energy final
• Scenario: A boulder resting on a hilltop
• What kind of energy does the boulder have at the top of
the hill?
• What will happen to that energy as the boulder rolls down
the hill? Why?
• What kind of energy does the boulder have as it rolls down
the hill?
• What will happen to this energy as the boulder rolls down
the hill? Why?
• What would happen to the two types of energy mentioned
if the hill on which the boulder sits was much taller?
Work
• Two things must occur for work to be done.
1- a force must be applied
2- something must move as a result of that force
• Work = force x distance
Or
W=fd unit= Nm or J (joules)
Power
• Power = rate at which work is done.
P= W
t
(unit is 1 J/s OR 1 W (watts) )
(i.e. 40 W = 40 J/s)
1 horsepower = 746 Watts
Making Work Easier
• A device that makes work easier is a
machine.
• They make work easier by increasing the
force applied to an object
• examples: crowbar (opening a box) a
ramp (raising a box) a screwdriver
(increase the force applied to a screw)
Simple Machines-Six types of simple machines:
• Lever a bar that is free to pivot or turn
• Pulley a grooved wheel with a rope , chain or cable
running along a groove
• Wheel and Axle consisting of a shaft or axle attached
to the center of a large wheel, such that they rotate
together (screw drivers, doorknobs, faucet handles
• Inclined plane a sloping surface such as a ramp that
reduces the amount of force required to do work
• Screw an inclined plain wrapped in spiral around a
cylindrical post
• Wedge an inclined plane moves through an object or
material (an axe blade or knife
Conservation of energy
• When you do work on a machine your
transferring energy to the machine.
• The force that is applied to the machine is
called the input force And the force applied
by the machine is called the output force.
• Meaning work in is equal to work out
Win = Wout
Fin Din = Fout Dout
Mechanical Advantage
•