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Work & Energy Chapter 12 Notes. Work / Work has a specific meaning in science - Work is done when a...
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Transcript of Work & Energy Chapter 12 Notes. Work / Work has a specific meaning in science - Work is done when a...
WorkWork
Work has a specific meaning in science - Work is done when a force causes a change in the position of an object
Work has a specific meaning in science - Work is done when a force causes a change in the position of an object
WorkWork
The equation for work is:
Work = Force x distance
W = F * d
The equation for work is:
Work = Force x distance
W = F * d
WorkWork Unit for work is a Joule (J)
J = N * m
J = [(kg * m) / s2] * m
J = (kg * m2) / s2
Unit for work is a Joule (J)
J = N * m
J = [(kg * m) / s2] * m
J = (kg * m2) / s2
Work ExampleWork Example
Find the work done when a father lifts his daughter up into the air if he lifts her 1.5 m and uses a force of 160 N.
Find the work done when a father lifts his daughter up into the air if he lifts her 1.5 m and uses a force of 160 N.
PowerPower
Power is defined as work/time
Power = Work / time
P = W / ∆t
Power is defined as work/time
Power = Work / time
P = W / ∆t
PowerPower
The units for power is the Watt (W)
Watt = Joule / second
W = (kg * m2) / s3
The units for power is the Watt (W)
Watt = Joule / second
W = (kg * m2) / s3
Power ExamplePower Example
A race car zooms down a race track of length 200 m. The car has a force of 400 N pushing it forward. The car finishes the race in 5 seconds. Find the work done on the car Find the power of this car
A race car zooms down a race track of length 200 m. The car has a force of 400 N pushing it forward. The car finishes the race in 5 seconds. Find the work done on the car Find the power of this car
EnergyEnergy
The world around is full of energy
You can see it, hear it, possess it, store it, etc
Living organisms cannot survive without energy
The world around is full of energy
You can see it, hear it, possess it, store it, etc
Living organisms cannot survive without energy
EnergyEnergy
Energy is often defined as: The ability to do work
The unit for energy is the joule How does this compare to the unit for work?
Energy is often defined as: The ability to do work
The unit for energy is the joule How does this compare to the unit for work?
EnergyEnergy
Two major types of mechanical energy
Potential energy Based on position/configuration or an object
Kinetic energy Based on motion of an object
Two major types of mechanical energy
Potential energy Based on position/configuration or an object
Kinetic energy Based on motion of an object
Potential EnergyPotential Energy
Gravitational potential energy Energy stored by gravity
Elastic potential energy Energy stored by an object that stretches
Gravitational potential energy Energy stored by gravity
Elastic potential energy Energy stored by an object that stretches
Potential EnergyPotential Energy
Gravitational potential energy Depends on the mass and height of an object
PE = mass x gravity x height
PE = m * g * h
Gravitational potential energy Depends on the mass and height of an object
PE = mass x gravity x height
PE = m * g * h
Potential Energy ExamplePotential Energy Example
Find the PE of a 20 kg object elevated 5 meters above the ground.
Find the PE of a 20 kg object elevated 5 meters above the ground.
Kinetic EnergyKinetic Energy Energy of a moving object caused by the motion of the object is called kinetic energy
Depends on mass and speed of object
KE = (1/2) (m * v2)
Energy of a moving object caused by the motion of the object is called kinetic energy
Depends on mass and speed of object
KE = (1/2) (m * v2)
Kinetic Energy ExampleKinetic Energy Example
Find the KE of a 400 kg object moving with a speed of 5 m/s
Find the KE of a 400 kg object moving with a speed of 5 m/s
Kinetic EnergyKinetic Energy
Does KE depend more on mass or more on speed?
Does KE depend more on mass or more on speed?
Other forms of EnergyOther forms of Energy
Non-mechanical energy types Solar Electrical Nuclear Chemical Light Sound
Non-mechanical energy types Solar Electrical Nuclear Chemical Light Sound
Energy TransformationsEnergy Transformations Energy can change forms from one type to another As a ball drops PE is transformed into KE
When a slingshot is fired PE is transformed into KE
Flipping a light switch will transform electricity to light
When a car slows KE is transformed into thermal energy (due to friction)
Energy can change forms from one type to another As a ball drops PE is transformed into KE
When a slingshot is fired PE is transformed into KE
Flipping a light switch will transform electricity to light
When a car slows KE is transformed into thermal energy (due to friction)
Conservation of EnergyConservation of Energy
Law states: Energy cannot be created Energy cannot be destroyed Energy can be transformed from one form to another form
Law states: Energy cannot be created Energy cannot be destroyed Energy can be transformed from one form to another form
Conservation of EnergyConservation of Energy
Sometimes it seems like energy is “lost” or destroyed
Can you explain where this energy went?
Sometimes it seems like energy is “lost” or destroyed
Can you explain where this energy went?
Conservation of EnergyConservation of Energy
Identify the transformations of energy for a pendulum as it swings back and forth
Identify the transformations of energy for a pendulum as it swings back and forth
Conservation of EnergyConservation of Energy
Identify the transformations of energy for a toy car that is wound up and then released
Identify the transformations of energy for a toy car that is wound up and then released