Notes Outline Work, Energy and Power
A. Definitions and formulas
1. Work- Work is done when a force acts on an object in the direction of its motion. Work causes a change in the kinetic energy, potential energy or both of the object.
Units – Joules = N-m
2. Potential Energy- energy possessed by an object due to its position
Gravitational potential energy depends on mass, gravitational field strength ‘g’ and location on the field ‘h’.
Units - Joules
3. Kinetic energy – energy associated with motion KE = ½ mv2
4. Power- rate that work is done or energy transferred.
P = Work/ time.
Units: Watts (Joules/sec)
B. Forces do work when they act over a distance
give an example below of each force doing work.
(Remember, the force and the distance moved must be parallel to each other!)
1. Applied force-
2. gravity-
Mr. Linares
3. tension-
4. friction-
Ben Townsend
5. Calculating Work: pg. 119 # 2-4; pg. 120 # 21-23
C. Work to Energy
1. Energy is the ability to do work
And
Work is the mechanical transfer of energy
Work,Heat,andEnergy
Energyisconserved,butcanbeconvertedtodifferenttypes
WaystoTransferEnergyIntoorOutofASystem
Work–transfersbyapplyingaforceandcausingadisplacementofthepointofapplicationoftheforce.
MechanicalWaves–allowadisturbancetopropagatethroughamedium.
Heat–isdrivenbyatemperaturedifferencebetweentworegionsinspace.
MatterTransfer–matterphysicallycrossestheboundaryofthesystem,carryingenergywithit.
ElectricalTransmission–transferisbyelectriccurrent.
ElectromagneticRadiation–energyistransferredbyelectromagneticwaves
W=DPE=DKE=DU
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Sec2.1:ReviewingMechanicalConceptsofEnergy
Work and energy are both measured in Joules (kg*m2/s2)
Work is done by a force on a mass.
Energy is possessed by a mass due to its properties and position.
2. When you lift a mass UP against gravity:
h
W = F x D
W = Weight x d m
W = mg h
This Work raises the mass, which now has ______.
If it falls on your foot, it will surely do work on your foot!
Formula:
D. Potential Energy – Stored energy due to work that was done
1. Examples
Work Resulting Potential Energy
2. Gravitational Potential Energy
W =
F x d
PE = mgh
a) Lifting a 1 kg book onto the 1 m desk
b) Walking up the stairs : 3 m.
c) A 0.2 kg ball is thrown up 2.5 m.
d) The ball falls down 2.5 m.
E. Energy in Motion –
1. Formula-
As the speed of a moving object increases, its energy, and therefore its ability to do work, does not increase in a
Linear way
2.) but as the square of the velocity:
speed energy
a) What does this say about the braking force needed to stop a car as its speed increases?
b) What happens if the brakes lock up?
Energy problem-solving: pg. 119 # 7,9 pg. 120 # 27,33
pg. 121 #45
F. Power
1. Definition-
2. Formula-
3. Does this definition differ from the “everyday” definition of power?
4. What is the advantage of a “powerful” machine?
5. Calculating power
Pg. 119 #5, pg. 120 #23,26, pg. 121 #44
Name ______
Work-Energy Mini Labs
I. Work to Energy
A. Objective
B. Hypothesis:
Which sample will have the larger temperature change?
C. Procedure:
1. At each station, measure out _____ grams of sample material. Place the sample in the insulated container.
2. Measure the temperature of the sample and record
3. Place the top on the insulated container and shake it for one minute exactly.
4. Quickly measure the temperature of the sample and record.
D. Data
Sample material starting ending change
temp temp
E. Questions
1. Analyze the design of this experiment. Identify the independent variable, dependent variable, and two control variables.
2. Temperature is a measure of the energy of the sample. Where did the increased energy come from?
3. Make a diagram showing the flow of energy and work. Start with the sun and end with the particles in the sample.
Name ______
II. Energy to Work
A. Objective : What will be the relationship between the potential energy of the object and the distance it travels on the flat ground? Will this relationship be the same for all objects?
B. Hypothesis:
C. Procedure:
1. At your ramp station, release the object from heights of 5, 10 and 15 cm.
2. For each height, record the distance the object travels before coming to a stop.
Object ______mass ______kg
D. Data
Height distance PE = mgh PE/d = F
E. Questions
1. What factors determined the amount of energy the objects started with?
2. What force did work on the objects and dissipated the energy?
3. Where did the energy go?
4. Comparing to other groups, did the did the potential energy and distance stay proportional for all objects?
F. Energy conservation
1. PE (grav) to KE
Falling object:
2. KE to PE (pendulum)
3. Energy Conservation Problem solving
Pg. 119 #8 pg.120 #12 pg. 121 #36, 42, 43
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