Work, Energy, & Power Chapter 6. Let’s start with WORK… Work is only done if an object is...
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Transcript of Work, Energy, & Power Chapter 6. Let’s start with WORK… Work is only done if an object is...
![Page 1: Work, Energy, & Power Chapter 6. Let’s start with WORK… Work is only done if an object is displaced by the force, in the same direction as the force!](https://reader035.fdocuments.net/reader035/viewer/2022062421/56649d6f5503460f94a50c3a/html5/thumbnails/1.jpg)
Work, Energy, & PowerChapter 6
![Page 2: Work, Energy, & Power Chapter 6. Let’s start with WORK… Work is only done if an object is displaced by the force, in the same direction as the force!](https://reader035.fdocuments.net/reader035/viewer/2022062421/56649d6f5503460f94a50c3a/html5/thumbnails/2.jpg)
Let’s start with WORK…
• Work is only done if an object is displaced by the force, in the same direction as the force!
![Page 3: Work, Energy, & Power Chapter 6. Let’s start with WORK… Work is only done if an object is displaced by the force, in the same direction as the force!](https://reader035.fdocuments.net/reader035/viewer/2022062421/56649d6f5503460f94a50c3a/html5/thumbnails/3.jpg)
Work
• Work is the process of changing the energy of the system
• Units: Joules– 1,000 J = 1kJ (1kilo-Joule)
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How do we do Work?
1. Changing the speed of an object– Catching a baseball– Applying brakes of your car
2. By doing work against another force.– Doing a pull-up– Bench press– Or simply getting up out of your chair
W =F∆sCosΘ
![Page 5: Work, Energy, & Power Chapter 6. Let’s start with WORK… Work is only done if an object is displaced by the force, in the same direction as the force!](https://reader035.fdocuments.net/reader035/viewer/2022062421/56649d6f5503460f94a50c3a/html5/thumbnails/5.jpg)
Practice Problems
• Work is only done if the object is displaced in the same direction as the force.
![Page 6: Work, Energy, & Power Chapter 6. Let’s start with WORK… Work is only done if an object is displaced by the force, in the same direction as the force!](https://reader035.fdocuments.net/reader035/viewer/2022062421/56649d6f5503460f94a50c3a/html5/thumbnails/6.jpg)
Solutions
• A: W = Fs Cos 0°= 100N x 5 m = 500J
• B: W = Fs CosΘ = [100N Cos (30°)] x 5 m = 433J
• C: W = Fs Cos 0° = (mg) d = (15kg x 9.8m/s2) 5 m = 750J
30°
100N
![Page 7: Work, Energy, & Power Chapter 6. Let’s start with WORK… Work is only done if an object is displaced by the force, in the same direction as the force!](https://reader035.fdocuments.net/reader035/viewer/2022062421/56649d6f5503460f94a50c3a/html5/thumbnails/7.jpg)
Solutions
• A: W = Fs Cos 0°= 100N x 5 m = 500J
• B: W = Fs CosΘ = [100N Cos (30°)] x 5 m = 433J
• C: W = Fs Cos 0° = (mg) d = (15kg x 9.8m/s2) 5 m = 750J
30°
100N
![Page 8: Work, Energy, & Power Chapter 6. Let’s start with WORK… Work is only done if an object is displaced by the force, in the same direction as the force!](https://reader035.fdocuments.net/reader035/viewer/2022062421/56649d6f5503460f94a50c3a/html5/thumbnails/8.jpg)
Solutions
• A: W = Fs Cos 0°= 100N x 5 m = 500J
• B: W = Fs CosΘ = [100N Cos (30°)] x 5 m = 433J
• C: W = Fs Cos 0° = (mg) d = (15kg x 9.8m/s2) 5 m = 750J
30°
100N
![Page 9: Work, Energy, & Power Chapter 6. Let’s start with WORK… Work is only done if an object is displaced by the force, in the same direction as the force!](https://reader035.fdocuments.net/reader035/viewer/2022062421/56649d6f5503460f94a50c3a/html5/thumbnails/9.jpg)
Power
• Power is simply the rate at which work is done.
• The faster we do Work… the more powerful our action is
• The slower we do that same Work… the less powerful our action is
What makes the backhoe loader more POWERFUL?
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Power
• Power is simply the rate at which work is done
• P = W / t• Units: Watt
![Page 11: Work, Energy, & Power Chapter 6. Let’s start with WORK… Work is only done if an object is displaced by the force, in the same direction as the force!](https://reader035.fdocuments.net/reader035/viewer/2022062421/56649d6f5503460f94a50c3a/html5/thumbnails/11.jpg)
From Work to Energy
•CAUSE… WORK
•EFFECT… ∆ENERGY
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The Many Forms of Energy
• Energy is the ability of an object to cause a change in itself or the environment– Thermal - Radiant– Nuclear - Light– Chemical - Sound– Electrical - Electrochemical– Motion (KE) - Gravitational (PE)
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Mechanical Energy
• There are two types:
• Gravitational Potential Energy
• Kinetic Energy
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Can Gravity Do Work?
• Recall… • Of Course!
– like any force, the gravitational force can cause an object to be displaced.
– We call this work, Gravitational potential energy W = F∆s CosΘ
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Work and Gravitational Potential Energy
– We know…W = Fs CosΘ– Or in the specific case of gravity doing the
work we know F=mg – So… W = (mg)s CosΘ– So, we could say… W = FsCosΘ = mgh– You might recall… PE = mgh– Work = FsCosΘ = mgh = Gravitational
Potential Energy (PE)
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Gravitational Potential Energy (GPE)
• Known as energy of position
• Measured in Joules• GPE = mgh• Example: How much
GPE does a 4500 kg roller coaster possess if it is poised on top of a 48 m high hill?
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Kinetic Energy
• Start with equation 7Vf
2 = Vi2 + 2ad
• Substitute F/m in for a (F=ma)
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Kinetic Energy
• ThereforeVf
2 = Vi2 + 2Fd/m
• Solve for FdVf
2 - Vi2 = 2Fd/m
1/2Vf2 – 1/2Vi
2 = Fd/m
1/2mVf2 – 1/2mVi
2 = Fd
We change ‘d’ to ‘s’… and make sure in same direction with ‘CosΘ’
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Work-Energy Theorem
• Therefore1/2mV2 = Fs CosΘ
• Where 1/2mV2 is the Kinetic Energy (KE)• Where Fs CosΘ is the Work (W)
• Therefore W=Fs CosΘ=1/2 m∆v2 = ∆KE
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Kinetic Energy
• Known as energy of motion
• KE = ½ mv2
• Example: Same rollercoaster is traveling at 20.6 m/s. Kinetic Energy?
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The Law of Conservation of Mechanical Energy
• Energy can not be created or destroyed. It can only be transformed.
• One of the “Big Three” Conservation Laws (the others being Mass and Momentum)
• In other words, if you have 1,000 J of energy you can change it into other forms of energy without losing any of it. Every, single Joule is accounted for. *Read 6.4*
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Transform: Change forms
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You Make the Calculations:
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……..and these
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Homework
Chapter 6.1
•FOC #’s 1-2
•Problems #’s 1-4, 6-12