Warm UpWarm Up

List 3 forms of energy.List 3 forms of energy. List 3 ways energy can be List 3 ways energy can be

transformed.transformed.

Energy Energy TransformationTransformationWhen energy in an object goes from When energy in an object goes from one form to another.one form to another.

- The energy of a pendulum bob - The energy of a pendulum bob goes from potential to kinetic and goes from potential to kinetic and back againback again

- A skydiver's energy goes from - A skydiver's energy goes from potential, to kinetic, to thermalpotential, to kinetic, to thermal

- A car's energy goes from - A car's energy goes from kinetic to thermal while brakingkinetic to thermal while braking

If A pendulum's bob has a mass of 0.2 If A pendulum's bob has a mass of 0.2 kg. If it is released from a height of kg. If it is released from a height of 0.3 m, what are:0.3 m, what are:– A) Its total energy?A) Its total energy?– B) Kinetic energy at the bottom of its B) Kinetic energy at the bottom of its

path?path?– C) Its velocity at the bottom of its path?C) Its velocity at the bottom of its path?– D)Its velocity at a height of 0.1 m? D)Its velocity at a height of 0.1 m?

A skydiver jumps from an airplane A skydiver jumps from an airplane which is 5000 m above the surface of which is 5000 m above the surface of the earth, if his parachute deploys at the earth, if his parachute deploys at 2000 m, what was his velocity just 2000 m, what was his velocity just before the parachute is deployed?before the parachute is deployed?

Make a graph of his potential and Make a graph of his potential and kinetic energy, relative to his height. kinetic energy, relative to his height. After deploying his parachute his After deploying his parachute his velocity is a constant 10 m/svelocity is a constant 10 m/s

Terminal VelocityTerminal Velocity What does terminal velocity mean?What does terminal velocity mean?

Do falling objects accelerate for the Do falling objects accelerate for the entire time that they are falling? Why entire time that they are falling? Why or why not?or why not?

What does this mean in terms of What does this mean in terms of energy?energy?

Terminal Velocity – When the force of Terminal Velocity – When the force of gravity downward on an object is gravity downward on an object is equaled by the force of wind equaled by the force of wind resistance upward, then a falling resistance upward, then a falling object falls at a constant velocity.object falls at a constant velocity.– Depends on the mass, and surface area Depends on the mass, and surface area

of the falling objectof the falling object– For humans it is about 120 mph or 54 m/sFor humans it is about 120 mph or 54 m/s

How far (in physics land) would a How far (in physics land) would a person have to fall before they reach person have to fall before they reach their terminal velocity?their terminal velocity?

In real life it is farther than this, why?In real life it is farther than this, why? Where does the energy go as a Where does the energy go as a

person's height (PE) decreases, person's height (PE) decreases, without their velocity (KE) increasing?without their velocity (KE) increasing?

ThermodynamicsThermodynamics

Explains the transfer of heat Explains the transfer of heat energy.energy.– 0th Law: If object A is in equilibrium 0th Law: If object A is in equilibrium

with object B, and Object B is in with object B, and Object B is in equilibrium with object C, then A and C equilibrium with object C, then A and C are also in equilibriumare also in equilibrium

– 11stst Law: the change in the internal Law: the change in the internal energy of a closed system is equal to energy of a closed system is equal to the sum of the amount of heat energy the sum of the amount of heat energy supplied to the system and the work supplied to the system and the work done on the systemdone on the system

ThermodynamicsThermodynamics

22ndnd Law: Entropy (disorder) Law: Entropy (disorder) increasesincreases

33rdrd Law: If the temperature Law: If the temperature reaches absolute 0, entropy = 0. reaches absolute 0, entropy = 0.

EnginesEngines There are physical reasons why we There are physical reasons why we

can't build a perfect engine. can't build a perfect engine. Perfect Engine: Energy in = Perfect Engine: Energy in =

mechanical energy out.mechanical energy out. Efficiency is the rating that tells us Efficiency is the rating that tells us

how good a given engine is at how good a given engine is at converting energy in, into energy converting energy in, into energy out. out. – Automobile engines and refrigerators Automobile engines and refrigerators

are very inefficient while heaters are are very inefficient while heaters are relatively efficientrelatively efficient

ElectricityElectricity

As a society we are very As a society we are very concerned with how we can concerned with how we can convert mechanical energy convert mechanical energy (occurring naturally) and turn it (occurring naturally) and turn it into electrical energy.into electrical energy.

PowerPower

Power = energy/timePower = energy/time– Appliances and lightbulbs are rated Appliances and lightbulbs are rated

by the power they useby the power they use– Electric bills come in terms of kWhElectric bills come in terms of kWh

Forms of energy (power Forms of energy (power plants)plants) Nuclear (Fission or FusionNuclear (Fission or Fusion SolarSolar WindWind CoalCoal OilOil HydroelectricHydroelectric GeothermalGeothermal TidalTidal

In classIn class

Design a Rube Goldberg machine Design a Rube Goldberg machine with 3 steps, explain how energy is with 3 steps, explain how energy is transferred/transformed during transferred/transformed during and between each step.and between each step.

Homework: noneHomework: none

HomeworkHomework

Design a 5 step Rube Goldberg Design a 5 step Rube Goldberg machine. Include labels and machine. Include labels and descriptions of where the energy descriptions of where the energy goes (transfers) and how it is goes (transfers) and how it is transformed at and between each transformed at and between each step.step.