Work – Energy TheoremFeb. 19 & 20

10 minutes to complete #1-5!

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It increased Friction, transfers of energy, etc.

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•If work is done on an object, the object acquires the ability to do work

When work is done to raise a bowling ball, the bowling ball acquires the ability to do work on an object it hits when it falls.

9.3 Mechanical Energy

When work is done to wind a spring mechanism, the spring acquires the ability to do work on various gears to run a clock, drive a car, ring a bell, or sound an alarm.

9.3 Mechanical Energy

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•If work is done on an object, the object acquires the ability to do work•Something is acquired in order for an object to have the ability to do work•The “something” is MECHANICAL ENERGY2 types: PE & KE

8.4 POTENTIAL ENERGY, aka PE (pgs 106-107)An object may store energy by virtue of its positionThis energy that is stored and held in readiness is called

potential energy (PE)In other words, this PE has the potential of doing work

on somethingExamples:

Compressed spring or stretched rubber band (tension)Electrical energy (battery)Gravitational potential energy

Grav. PE = mgh The amount of gravitational potential energy possess by an

object is equal to the work done against gravity in lifting it.

8.5 KINETIC ENERGY, aka KE (pg 108)KINETIC ENERGY IS NOT MOMENTUM!If an object is moving, then it is capable of doing

workIt has energy of motion, or KINETIC ENERGYThe KE of an object depends on its mass and on its

speedKE = ½ m v2

The KE of a moving object is equal to the WORK required to;Bring it TO that speed, from rest….orThe work the object CAN do while being brought to rest.

The WORK-ENERGY THEOREM

THEN…

ENERGYchanges

IF…

IF…

WORKIs done

THEN…

Like a wrecking ball!Not this one!!!! (That’s a train

wreck)

Like a wrecking ball!This one!

Graphic Organizer (WRITE THIS!)

THEN…

ENERGYchanges

IF…

IF…

WORKIs done

THEN…

W = ΔE

Graphic Organizer (WRITE THIS!)

THEN…

ENERGYchanges

IF…

IF…

WORKIs done

THEN…

W = ΔE

∑E = PE + KE

Graphic Organizer (WRITE THIS!)

THEN…

ENERGYchanges

IF…

IF…

WORKIs done

THEN…

W = ΔE

Mechanical Energy (M.E)

Potential Energy (P.E)

Kinetic Energy (K.E)

∑E = PE + KE

In addition to…Work Energy TheoremAnd the different types of PE & KE

The other main point for today is…

MFMcGraw Ch07 - Energy - Revised: 2/21/10 17

Law of Conservation of EnergyEnergy cannot be created or destroyed; it may be transformed from one form into another, but the total amount of energy never changes.

MFMcGraw Ch07 - Energy - Revised: 2/21/10 18

Conservation of EnergyExample: Energy transforms without net

loss or net gain in the operation of a pile driver.

Part of the PE of the wound spring changes into KE. The remaining PE goes into heating the machinery and the surroundings due to friction. No energy is lost.

Conservation of Energy

Everywhere along the path of the pendulum bob, the sum of PE and KE is the same. Because of the work done against friction, this energy will eventually be transformed into heat.

Conservation of Energy

Do #1-9!

P.E

P.E

P.E

P.E

P.E

K.E

K.E

K.E

K.E

Finish up to & INCLUDING HERE today (#5 on the last sheet of paper)(anything not finished is HW)

EXIT SLIP – on scrap

ID: NAME: DATE: CLASS:1. Is it possible for an object to have both PE &

KE simultaneously? EXPLAIN

2. What did you learn today that you are REALLY confident about?

3. What is confusing you?