Work & EnergyWork & Energy

Chapter 12 NotesChapter 12 Notes

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

Conservation of EnergyConservation of Energy

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

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