chapter 10: energy and work...work-energy theorem •the total energy of a system changes by the...
TRANSCRIPT
![Page 1: Chapter 10: Energy and Work...Work-Energy Theorem •The total energy of a system changes by the amount of work done on it. •When a net force performs work on an object, the result](https://reader034.vdocuments.net/reader034/viewer/2022050300/5f691e7dce69411fad3a1f58/html5/thumbnails/1.jpg)
Slide 10-2
Chapter 10: Energy and Work
![Page 2: Chapter 10: Energy and Work...Work-Energy Theorem •The total energy of a system changes by the amount of work done on it. •When a net force performs work on an object, the result](https://reader034.vdocuments.net/reader034/viewer/2022050300/5f691e7dce69411fad3a1f58/html5/thumbnails/2.jpg)
Forms of Energy
Mechanical Energy
Ug UsK
Thermal Energy
Eth
Other forms include
Echem Enuclear
![Page 3: Chapter 10: Energy and Work...Work-Energy Theorem •The total energy of a system changes by the amount of work done on it. •When a net force performs work on an object, the result](https://reader034.vdocuments.net/reader034/viewer/2022050300/5f691e7dce69411fad3a1f58/html5/thumbnails/3.jpg)
The Basic Energy Model
Energy Transformations are changes of energy within the system from one form to another.
An exchange of energy between the system and environment is called an energy transfer. Two primary energy transfer processes: work and heat (APP2).
![Page 4: Chapter 10: Energy and Work...Work-Energy Theorem •The total energy of a system changes by the amount of work done on it. •When a net force performs work on an object, the result](https://reader034.vdocuments.net/reader034/viewer/2022050300/5f691e7dce69411fad3a1f58/html5/thumbnails/4.jpg)
Energy Transformations
Kinetic energy K = energy of motion
Potential energy U = energy of position
Thermal energy Eth = energy associated with temperature
System energy E = K + U + Eth + Echem + ...
Energy can be transformed within the system without loss.
Energy is a property of a system.
![Page 5: Chapter 10: Energy and Work...Work-Energy Theorem •The total energy of a system changes by the amount of work done on it. •When a net force performs work on an object, the result](https://reader034.vdocuments.net/reader034/viewer/2022050300/5f691e7dce69411fad3a1f58/html5/thumbnails/5.jpg)
Some Energy Transformations
Echem Ug K Eth
Echem Eth Us K Ug
![Page 6: Chapter 10: Energy and Work...Work-Energy Theorem •The total energy of a system changes by the amount of work done on it. •When a net force performs work on an object, the result](https://reader034.vdocuments.net/reader034/viewer/2022050300/5f691e7dce69411fad3a1f58/html5/thumbnails/6.jpg)
![Page 7: Chapter 10: Energy and Work...Work-Energy Theorem •The total energy of a system changes by the amount of work done on it. •When a net force performs work on an object, the result](https://reader034.vdocuments.net/reader034/viewer/2022050300/5f691e7dce69411fad3a1f58/html5/thumbnails/7.jpg)
Question:
If a system is isolated, the total energy of the system
A. increases constantly.B. decreases constantly.C. is constant.D. depends on work into the system.E. depends on work out of the system.
![Page 8: Chapter 10: Energy and Work...Work-Energy Theorem •The total energy of a system changes by the amount of work done on it. •When a net force performs work on an object, the result](https://reader034.vdocuments.net/reader034/viewer/2022050300/5f691e7dce69411fad3a1f58/html5/thumbnails/8.jpg)
Answer
If a system is isolated, the total energy of the system
A. increases constantly.B. decreases constantly.C. is constant.D. depends on work into the system.E. depends on work out of the system.
![Page 9: Chapter 10: Energy and Work...Work-Energy Theorem •The total energy of a system changes by the amount of work done on it. •When a net force performs work on an object, the result](https://reader034.vdocuments.net/reader034/viewer/2022050300/5f691e7dce69411fad3a1f58/html5/thumbnails/9.jpg)
![Page 10: Chapter 10: Energy and Work...Work-Energy Theorem •The total energy of a system changes by the amount of work done on it. •When a net force performs work on an object, the result](https://reader034.vdocuments.net/reader034/viewer/2022050300/5f691e7dce69411fad3a1f58/html5/thumbnails/10.jpg)
Energy Transfers
These change the energy of the system.
Interactions with the environment.
Work is the mechanical transfer of energy to or from a system via pushes and pulls.
![Page 11: Chapter 10: Energy and Work...Work-Energy Theorem •The total energy of a system changes by the amount of work done on it. •When a net force performs work on an object, the result](https://reader034.vdocuments.net/reader034/viewer/2022050300/5f691e7dce69411fad3a1f58/html5/thumbnails/11.jpg)
Energy Transfers: Work
W K W Eth
W Us
![Page 12: Chapter 10: Energy and Work...Work-Energy Theorem •The total energy of a system changes by the amount of work done on it. •When a net force performs work on an object, the result](https://reader034.vdocuments.net/reader034/viewer/2022050300/5f691e7dce69411fad3a1f58/html5/thumbnails/12.jpg)
W = F·d (Units: N·m = Joule)where F and d (displacement) are parallel to one another
positive work negative work
W = F·d W = (F·cos) d
![Page 13: Chapter 10: Energy and Work...Work-Energy Theorem •The total energy of a system changes by the amount of work done on it. •When a net force performs work on an object, the result](https://reader034.vdocuments.net/reader034/viewer/2022050300/5f691e7dce69411fad3a1f58/html5/thumbnails/13.jpg)
Work Done by Force at an Angle to DisplacementRecall: Force and Displacement have to be parallel for work to be done.
![Page 14: Chapter 10: Energy and Work...Work-Energy Theorem •The total energy of a system changes by the amount of work done on it. •When a net force performs work on an object, the result](https://reader034.vdocuments.net/reader034/viewer/2022050300/5f691e7dce69411fad3a1f58/html5/thumbnails/14.jpg)
Work
![Page 15: Chapter 10: Energy and Work...Work-Energy Theorem •The total energy of a system changes by the amount of work done on it. •When a net force performs work on an object, the result](https://reader034.vdocuments.net/reader034/viewer/2022050300/5f691e7dce69411fad3a1f58/html5/thumbnails/15.jpg)
• Work makes you mad…
• Power makes you mad over time…
• Get it?
• Work makes you m·a·d…
• Power makes you m·a·d/t
![Page 16: Chapter 10: Energy and Work...Work-Energy Theorem •The total energy of a system changes by the amount of work done on it. •When a net force performs work on an object, the result](https://reader034.vdocuments.net/reader034/viewer/2022050300/5f691e7dce69411fad3a1f58/html5/thumbnails/16.jpg)
Energy Equations
![Page 17: Chapter 10: Energy and Work...Work-Energy Theorem •The total energy of a system changes by the amount of work done on it. •When a net force performs work on an object, the result](https://reader034.vdocuments.net/reader034/viewer/2022050300/5f691e7dce69411fad3a1f58/html5/thumbnails/17.jpg)
Kinetic Energy
• KE = ½ m(v)2 (Translational Kinetic Energy)
• Looking at this equation, what does KE depend on?
• Mass and Speed. KE is called energy of motion.
• Work can change KE (work energy theorem.) W = ΔKE
• F •d = ½ m vf2 – ½ m vi
2
![Page 18: Chapter 10: Energy and Work...Work-Energy Theorem •The total energy of a system changes by the amount of work done on it. •When a net force performs work on an object, the result](https://reader034.vdocuments.net/reader034/viewer/2022050300/5f691e7dce69411fad3a1f58/html5/thumbnails/18.jpg)
Drivers Ed Question…While driving, if you double your speed, how much more distance
is needed to stop?
![Page 19: Chapter 10: Energy and Work...Work-Energy Theorem •The total energy of a system changes by the amount of work done on it. •When a net force performs work on an object, the result](https://reader034.vdocuments.net/reader034/viewer/2022050300/5f691e7dce69411fad3a1f58/html5/thumbnails/19.jpg)
Drivers Ed Question…While driving, if you double your speed, how much more
distance is needed to stop?
• W = ΔKE
• F •d = ½ m vf2 – ½ m vi
2
• F •d = ½ m vf2 – ½ m vi
2
• F •d = 0 – ½ m vi2
• d vi2
• (2vi)2 4d
• Doubling vi, or 2x vi, will result in a 22x d or 4x greater distance needing to stop!
![Page 20: Chapter 10: Energy and Work...Work-Energy Theorem •The total energy of a system changes by the amount of work done on it. •When a net force performs work on an object, the result](https://reader034.vdocuments.net/reader034/viewer/2022050300/5f691e7dce69411fad3a1f58/html5/thumbnails/20.jpg)
Relating Work to Kinetic Energy
• A constant net external force F acts over a displacement d and does work on the plane.
• As a result of the work done, the plane’s kinetic energy changes.
Displacement, d
![Page 21: Chapter 10: Energy and Work...Work-Energy Theorem •The total energy of a system changes by the amount of work done on it. •When a net force performs work on an object, the result](https://reader034.vdocuments.net/reader034/viewer/2022050300/5f691e7dce69411fad3a1f58/html5/thumbnails/21.jpg)
Work-Energy Theorem• The total energy of a system changes by the
amount of work done on it.• When a net force performs work on an
object, the result could be a change in the kinetic energy of the object.
• If the work done by the net force is positive, the kinetic energy of the object increases.
• If the work done by the net force is negative, the kinetic energy of the object decreases.
• If the work done by the net force is zero, the kinetic energy of the object remains the same, or unchanged.
• W = ΔKE = Kef - KEi
![Page 22: Chapter 10: Energy and Work...Work-Energy Theorem •The total energy of a system changes by the amount of work done on it. •When a net force performs work on an object, the result](https://reader034.vdocuments.net/reader034/viewer/2022050300/5f691e7dce69411fad3a1f58/html5/thumbnails/22.jpg)
Kinetic Energy
• Kinetic Energy can be solely translational K… K = ½ m v2
• Kinetic Energy can be solely rotational K…
• Or Kinetic Energy can be a combination of both… ball rolling down a ramp.
![Page 23: Chapter 10: Energy and Work...Work-Energy Theorem •The total energy of a system changes by the amount of work done on it. •When a net force performs work on an object, the result](https://reader034.vdocuments.net/reader034/viewer/2022050300/5f691e7dce69411fad3a1f58/html5/thumbnails/23.jpg)
Rotational Kinetic Energy
![Page 24: Chapter 10: Energy and Work...Work-Energy Theorem •The total energy of a system changes by the amount of work done on it. •When a net force performs work on an object, the result](https://reader034.vdocuments.net/reader034/viewer/2022050300/5f691e7dce69411fad3a1f58/html5/thumbnails/24.jpg)
![Page 25: Chapter 10: Energy and Work...Work-Energy Theorem •The total energy of a system changes by the amount of work done on it. •When a net force performs work on an object, the result](https://reader034.vdocuments.net/reader034/viewer/2022050300/5f691e7dce69411fad3a1f58/html5/thumbnails/25.jpg)
I = Moment of Inertia, M = Mass, R = radius
![Page 26: Chapter 10: Energy and Work...Work-Energy Theorem •The total energy of a system changes by the amount of work done on it. •When a net force performs work on an object, the result](https://reader034.vdocuments.net/reader034/viewer/2022050300/5f691e7dce69411fad3a1f58/html5/thumbnails/26.jpg)
Gravitational PE• The total energy of a system changes by the
amount of work done on it. (Work-Energy Theorem)
• Ug = GPE = magΔh
• What does GPE depend on?
• Mass, acceleration due to gravity & height.
• GPE is called energy of location or position.
• ΔGPE does not care about that path taken, just the change in height.
• W= ΔGPE = magΔh
![Page 27: Chapter 10: Energy and Work...Work-Energy Theorem •The total energy of a system changes by the amount of work done on it. •When a net force performs work on an object, the result](https://reader034.vdocuments.net/reader034/viewer/2022050300/5f691e7dce69411fad3a1f58/html5/thumbnails/27.jpg)
Work done by the force of gravity
• Gravity exerts a force mg on the basketball. Work is done by the gravitational force as the basketball falls from a height of ho to a height of hf (relative to the earth’s surface).
• d = ho - hf
• Wg = Fg d = mg (ho-hf)
![Page 28: Chapter 10: Energy and Work...Work-Energy Theorem •The total energy of a system changes by the amount of work done on it. •When a net force performs work on an object, the result](https://reader034.vdocuments.net/reader034/viewer/2022050300/5f691e7dce69411fad3a1f58/html5/thumbnails/28.jpg)
• An object can move along different paths in going from an initial height ho to a final height of hf. In each case, the work done by the gravitational force is the same, since the change in vertical distance is the same.
• d = ho - hf
• Wg = Fg d = mg (ho-hf)
• Note: ΔUg does not depend on path taken.
![Page 29: Chapter 10: Energy and Work...Work-Energy Theorem •The total energy of a system changes by the amount of work done on it. •When a net force performs work on an object, the result](https://reader034.vdocuments.net/reader034/viewer/2022050300/5f691e7dce69411fad3a1f58/html5/thumbnails/29.jpg)
Gravitational Potential Energy
• An object possessing energy by virtue of its position relative to earth is said to have gravitational potential energy.
• The hammer has the potential to do the work of driving the pile into the ground.
• Ug = PEg = mgh
• Wg = mg (Δh) = ΔUg
![Page 30: Chapter 10: Energy and Work...Work-Energy Theorem •The total energy of a system changes by the amount of work done on it. •When a net force performs work on an object, the result](https://reader034.vdocuments.net/reader034/viewer/2022050300/5f691e7dce69411fad3a1f58/html5/thumbnails/30.jpg)
Conservation of Energy• Energy cannot be created nor destroyed, but
energy can change from one form into another.
• ΔE = ΔUg + Δ KE + ΔUs = W
• For an isolated system, W = 0, or the total energy of an isolated system remains constant (is conserved).
• ΔE = ΔGPE + Δ KE = W = 0 (isolated system)
• Or another way to write it would be…
• Efinal = Einitial
![Page 31: Chapter 10: Energy and Work...Work-Energy Theorem •The total energy of a system changes by the amount of work done on it. •When a net force performs work on an object, the result](https://reader034.vdocuments.net/reader034/viewer/2022050300/5f691e7dce69411fad3a1f58/html5/thumbnails/31.jpg)
Question
If you raise an object to a greater height, you are increasing
A. kinetic energy. B. heat. C. potential energy.D. chemical energy.E. thermal energy.
![Page 32: Chapter 10: Energy and Work...Work-Energy Theorem •The total energy of a system changes by the amount of work done on it. •When a net force performs work on an object, the result](https://reader034.vdocuments.net/reader034/viewer/2022050300/5f691e7dce69411fad3a1f58/html5/thumbnails/32.jpg)
Answer
If you raise an object to a greater height, you are increasing
A. kinetic energy. B. heat. C. potential energy.D. chemical energy.E. thermal energy.
![Page 33: Chapter 10: Energy and Work...Work-Energy Theorem •The total energy of a system changes by the amount of work done on it. •When a net force performs work on an object, the result](https://reader034.vdocuments.net/reader034/viewer/2022050300/5f691e7dce69411fad3a1f58/html5/thumbnails/33.jpg)
Checking Understanding
A skier is moving down a slope at a constant speed. What energy transformation is taking place?
A. K Ug
B. Ug Eth
C. Us Ug
D. Ug K
E. K Eth
![Page 34: Chapter 10: Energy and Work...Work-Energy Theorem •The total energy of a system changes by the amount of work done on it. •When a net force performs work on an object, the result](https://reader034.vdocuments.net/reader034/viewer/2022050300/5f691e7dce69411fad3a1f58/html5/thumbnails/34.jpg)
A skier is moving down a slope at a constant speed. What energy transformation is taking place?
A. K Ug
B. Ug Eth
C. Us Ug
D. Ug K
E. K Eth
Answer
![Page 35: Chapter 10: Energy and Work...Work-Energy Theorem •The total energy of a system changes by the amount of work done on it. •When a net force performs work on an object, the result](https://reader034.vdocuments.net/reader034/viewer/2022050300/5f691e7dce69411fad3a1f58/html5/thumbnails/35.jpg)
Checking Understanding
A child is on a playground swing, motionless at the highest point of his arc. As he swings back down to the lowest point of his motion, what energy transformation is taking place?
A. K Ug
B. Ug Eth
C. Us Ug
D. Ug K
E. K Eth
![Page 36: Chapter 10: Energy and Work...Work-Energy Theorem •The total energy of a system changes by the amount of work done on it. •When a net force performs work on an object, the result](https://reader034.vdocuments.net/reader034/viewer/2022050300/5f691e7dce69411fad3a1f58/html5/thumbnails/36.jpg)
Answer
A child is on a playground swing, motionless at the highest point of his arc. As he swings back down to the lowest point of his motion, what energy transformation is taking place?
A. K Ug
B. Ug Eth
C. Us Ug
D. Ug K
E. K Eth
![Page 37: Chapter 10: Energy and Work...Work-Energy Theorem •The total energy of a system changes by the amount of work done on it. •When a net force performs work on an object, the result](https://reader034.vdocuments.net/reader034/viewer/2022050300/5f691e7dce69411fad3a1f58/html5/thumbnails/37.jpg)
The Work-Energy Equation
![Page 38: Chapter 10: Energy and Work...Work-Energy Theorem •The total energy of a system changes by the amount of work done on it. •When a net force performs work on an object, the result](https://reader034.vdocuments.net/reader034/viewer/2022050300/5f691e7dce69411fad3a1f58/html5/thumbnails/38.jpg)
The Law of Conservation of Energy
![Page 39: Chapter 10: Energy and Work...Work-Energy Theorem •The total energy of a system changes by the amount of work done on it. •When a net force performs work on an object, the result](https://reader034.vdocuments.net/reader034/viewer/2022050300/5f691e7dce69411fad3a1f58/html5/thumbnails/39.jpg)
The Basic EquationKf Uf Eth Ki Ui
A few things to note:
•Work can be positive (work in) or negative (work out)
•We are, for now, ignoring heat.
•Thermal energy is…special. When energy changes to thermal energy, this change is irreversible.
![Page 40: Chapter 10: Energy and Work...Work-Energy Theorem •The total energy of a system changes by the amount of work done on it. •When a net force performs work on an object, the result](https://reader034.vdocuments.net/reader034/viewer/2022050300/5f691e7dce69411fad3a1f58/html5/thumbnails/40.jpg)
![Page 41: Chapter 10: Energy and Work...Work-Energy Theorem •The total energy of a system changes by the amount of work done on it. •When a net force performs work on an object, the result](https://reader034.vdocuments.net/reader034/viewer/2022050300/5f691e7dce69411fad3a1f58/html5/thumbnails/41.jpg)
Summary
![Page 42: Chapter 10: Energy and Work...Work-Energy Theorem •The total energy of a system changes by the amount of work done on it. •When a net force performs work on an object, the result](https://reader034.vdocuments.net/reader034/viewer/2022050300/5f691e7dce69411fad3a1f58/html5/thumbnails/42.jpg)
Summary