Work & Energy Chapter 12 Notes

Work / Work has a specific meaning in science - Work is done when a force causes a change in the position of an object

Work / The equation for work is: / Work = Force x distance W = F * d / The equation for work is: / Work = Force x distance W = F * d

Work / Unit for work is a Joule (J) J = N * m J = [(kg * m) / s 2 ] * m J = (kg * m 2 ) / s 2 / Unit for work is a Joule (J) J = N * m J = [(kg * m) / s 2 ] * m J = (kg * m 2 ) / s 2

Work 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.

Power / Power is defined as work/time / Power = Work / time / P = W / ∆t / Power is defined as work/time / Power = Work / time / P = W / ∆t

Power / The units for power is the Watt (W) / Watt = Joule / second / W = (kg * m 2 ) / s 3 / The units for power is the Watt (W) / Watt = Joule / second / W = (kg * m 2 ) / s 3

Power 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

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 / The world around is full of energy / You can see it, hear it, possess it, store it, etc / Living organisms cannot survive without energy

Energy / 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?

Energy / 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 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 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 Example / Find the PE of a 20 kg object elevated 5 meters above the ground.

Kinetic 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 * v 2 ) / 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 * v 2 )

Kinetic Energy Example / Find the KE of a 400 kg object moving with a speed of 5 m/s

Kinetic Energy / Does KE depend more on mass or more on speed?

Other forms of Energy / Non-mechanical energy types / Solar / Electrical / Nuclear / Chemical / Light / Sound / Non-mechanical energy types / Solar / Electrical / Nuclear / Chemical / Light / Sound

Energy 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 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 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 Energy / Identify the transformations of energy for a pendulum as it swings back and forth

Conservation of Energy / Identify the transformations of energy for a toy car that is wound up and then released

Conservation of Energy / Describe the energy transformations of a truck as it slows to a rest as it approaches a stop sign