3.1 energy forms and transformations · •gravitational potential energy: the stored energy of an...
TRANSCRIPT
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3.1 ENERGY FORMS AND TRANSFORMATIONS
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Vocabulary
ENERGY the ability to do work
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What is the purpose of a machine or device?
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• Many devices and machines convert, or transform, energy from one form to another.
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What forms of energy are there?
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Forms of Energy
• Electrical energy: the energy of charged particles
– occurs when electrons travel from place to place
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Forms of Energy
• Chemical Energy: the energy stored in chemicals.
– A type of potential (stored) energy
– Energy is released when chemicals react
– Examples: food, “batteries”, and fossil fuels contain chemical energy
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Forms of Energy
• Mechanical energy: the energy possessed by an object in motion.
– Examples: a person biking, a thrown baseball, the blades of a blender chopping food
https://youtu.be/3OmpnfL5PCw Will it blend?
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Forms of Energy
• Gravitational Potential Energy: the stored energy of an object at a height
– Examples: water falling from a height, object at the top of a cliff
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Forms of Energy
• Other forms of energy: thermal (heat), light, and sound
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What forms of energy are involved in using a
flashlight?
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Check Your Understanding
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Check Your Understanding
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Check Your Understanding
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Energy Transformations
• Energy is constantly changing from one form to another
– You are constantly transforming the chemical energy of your food to the mechanical energy of your body
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Energy Transformations
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3.3 MEASURING ENERGY INPUT AND OUTPUT
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Calculating
POWER (P)
The rate at which a device
converts energy. The unit of
power is the Watt (W).
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Calculating Power
• The faster a device converts energy, the greater its power rating.
• For an electrical device, we can calculate its power using the formula:
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Example 1
1. A hair dryer has a power rating of 1000 W. It is plugged into a 120 V outlet. What is the current flowing through the hair dryer?
I=8.3 A
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Example 2
2. A TV draws 1.5 A when connected to a 120 V outlet. What is the power rating of the TV?
P=180 W
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Example 3
3. A toaster connected to a 110 V power source has 6.0 A of current flowing through it. What is its power rating?
P=660 W
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Example 4
4. An oven has a power rating of 7000 W. If it draws 29.2 A of current, what is the
voltage of the outlet?
239.7 V
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Calculating
ENERGY (E) The ability to do work;
measured in Joules (J)
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Calculating
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Example 1
1.) A hair dryer has a power rating of 1000 W. If it takes a person 8.0 minutes to dry
their hair, how much energy did the hair dryer use?
E=480,000 J
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Example 2
2.) If the TV from question 2 above was on for 2.5 h, how much energy did it use?
E=1,620,000 J
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Example 3
3.) If a toaster uses 320 J of energy and takes 2.0 min to toast a bagel, what is its
power rating?
P=2.7 J
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Example 4
4.) A microwave oven has a power rating of 800 W. If you cook a roast in this oven for 30 min at high,
how many joules of electrical energy are converted into heat by the microwave?
E=1,440,000 J
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Input and Output Energy
• The job of a machine is often to transform energy from one form to at least one other form.
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Efficiency of Energy Transformation
• In addition to the form of output energy the machine is supposed to produce, there will always also be some heat produced.
• This means no machine is 100% efficient, because it is not transforming all of its input energy to its intended output energy
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No process can be 100% efficient.
Some energy will always remain in the form of
thermal (heat) energy
-- Second Law of Thermodynamics
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Calculating
• We can calculate how efficient a machine is by using the formula:
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Example 1
1.) Calculate the percent efficiency of the light bulb in figure 3.23 on the previous
page.
5%
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Example 2
2.) A wind turbine is able to transform 1,500,000 J of mechanical energy into
1,000,000 J of electrical energy. Calculate the efficiency of the wind turbine.
67%
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Example 3
3.) A small tractor is 12% efficient at producing useful output from input fuel. How
many joules of input fuel energy will this tractor need to produce 1000 J of useful output?
Input Energy=8333.3 J
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Example 4
4.) A 100 W bulb is turned on for 2.0 h. If the useful energy output is 25000 J of energy, what is the
efficiency of the bulb?
3.5%
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Check Your Understanding
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Check Your Understanding – Answers
1. a.) 1200 W
b.) 648,000 J
c.) 92.3%
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3.1 ENERGY FORMS AND TRANSFORMATIONS
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Vocabulary
ENERGY the ability to do work
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What is the purpose of a machine or device?
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• Many devices and machines convert, or transform, energy from one form to another.
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What forms of energy are there?
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Forms of Energy
• Electrical energy: the energy of charged particles
– occurs when electrons travel from place to place
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Forms of Energy
• Chemical Energy: the energy stored in chemicals.
– A type of potential (stored) energy
– Energy is released when chemicals react
– Examples: food, “batteries”, and fossil fuels contain chemical energy
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Forms of Energy
• Mechanical energy: the energy possessed by an object in motion.
– Examples: a person biking, a thrown baseball, the blades of a blender chopping food
https://youtu.be/3OmpnfL5PCw Will it blend?
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Forms of Energy
• Gravitational Potential Energy: the stored energy of an object at a height
– Examples: water falling from a height, object at the top of a cliff
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Forms of Energy
• Other forms of energy: thermal (heat), light, and sound
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What forms of energy are involved in using a
flashlight?
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Check Your Understanding
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Check Your Understanding
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Check Your Understanding
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Energy Transformations
• Energy is constantly changing from one form to another
– You are constantly transforming the chemical energy of your food to the mechanical energy of your body
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Energy Transformations
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3.3 MEASURING ENERGY INPUT AND OUTPUT
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Calculating
POWER (P)
The rate at which a device
converts energy. The unit of
power is the Watt (W).
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Calculating Power
• The faster a device converts energy, the greater its power rating.
• For an electrical device, we can calculate its power using the formula:
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Example 1
1. A hair dryer has a power rating of 1000 W. It is plugged into a 120 V outlet. What is the current flowing through the hair dryer?
I=8.3 A
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Example 2
2. A TV draws 1.5 A when connected to a 120 V outlet. What is the power rating of the TV?
P=180 W
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Example 3
3. A toaster connected to a 110 V power source has 6.0 A of current flowing through it. What is its power rating?
P=660 W
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Example 4
4. An oven has a power rating of 7000 W. If it draws 29.2 A of current, what is the
voltage of the outlet?
239.7 V
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Calculating
ENERGY (E) The ability to do work;
measured in Joules (J)
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Calculating
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Example 1
1.) A hair dryer has a power rating of 1000 W. If it takes a person 8.0 minutes to dry
their hair, how much energy did the hair dryer use?
E=480,000 J
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Example 2
2.) If the TV from question 2 above was on for 2.5 h, how much energy did it use?
E=1,620,000 J
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Example 3
3.) If a toaster uses 320 J of energy and takes 2.0 min to toast a bagel, what is its
power rating?
P=2.7 J
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Example 4
4.) A microwave oven has a power rating of 800 W. If you cook a roast in this oven for 30 min at high,
how many joules of electrical energy are converted into heat by the microwave?
E=1,440,000 J
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Input and Output Energy
• The job of a machine is often to transform energy from one form to at least one other form.
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Efficiency of Energy Transformation
• In addition to the form of output energy the machine is supposed to produce, there will always also be some heat produced.
• This means no machine is 100% efficient, because it is not transforming all of its input energy to its intended output energy
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No process can be 100% efficient.
Some energy will always remain in the form of
thermal (heat) energy
-- Second Law of Thermodynamics
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Calculating
• We can calculate how efficient a machine is by using the formula:
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Example 1
1.) Calculate the percent efficiency of the light bulb in figure 3.23 on the previous
page.
5%
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Example 2
2.) A wind turbine is able to transform 1,500,000 J of mechanical energy into
1,000,000 J of electrical energy. Calculate the efficiency of the wind turbine.
67%
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Example 3
3.) A small tractor is 12% efficient at producing useful output from input fuel. How
many joules of input fuel energy will this tractor need to produce 1000 J of useful output?
Input Energy=8333.3 J
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Example 4
4.) A 100 W bulb is turned on for 2.0 h. If the useful energy output is 25000 J of energy, what is the
efficiency of the bulb?
3.5%
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Check Your Understanding
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Check Your Understanding – Answers
1. a.) 1200 W
b.) 648,000 Jc.) 92.3%
2. a.) 240 Wb.) 69% efficient
3. a.) 6750 Vb.) 648,000 Jc.) 492,480 J
6. a.) 583,200,000 Jb.) 279,936,000 J of energy savedc.) The 52 W bulbs are more efficient.