SCIENCE 10
UNIT B: ENERGY FLOW IN TECHNOLOGICAL SYSTEMS
Unit Focus Questions
- Which came first: science or technology, and is it possible for technological development to take place without help from “pure” science
- How did effort to improve the efficiency of heat engines result in the formation of the first and second laws of thermodynamics?
- How can the analysis of moving objects help in the understanding of changes in kinetic energy, force, and work?
- Why are efficiency and sustainability important considerations in designing energy conversion technologies?
B2.0 Energy in mechanical systems can be described both numerically and graphically
Key Concepts
- Forms and interconversions of energy
- Mechanical energy conversions and work
- Design and function of technological systems
Learning Outcomes
- Illustrate, by use of example from natural and technological systems, that energy exists in a variety of forms.
- Describe, qualitatively, current and past technologies used to transform energy from one form to another, and that energy transfer technologies produce measurable changes in motion shape, or temperature
- Analyze and illustrate how the concept of energy developed from observation of heat and mechanical devices
- Describe the evidence for the presence of energy (i.e. Observable physical and chemical changes, and changes in motion, shape, or temperature)
- Derive the SI unit of energy and work, the joule from fundamental units.
- Define kinetic energy as energy due to motion, and define potential energy as energy due to relative condition or position
- Quantify kinetic energy using Ek=mv2/2 and relate this to energy transformations
- Relate gravitational potential energy to work done using Ep=mgh and W=Fd show that a change in energy is equal to work done on a system or ΔE=W
- Describe chemical energy as a form of potential energy
- Define gravitational potential energy as the work done against gravity
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B2.1 Forms of Energy
Chemical potential energy
Chemical potential energy - the energy stored in the chemical bonds of the materialEx. Explosives, gasoline
Electrical Energy and Magnetism
Electrical energy - the energy of a moving charge.Magnetic potential energy - the energy stored in the magnetic field around a magnet
Ex. Electrical lights are powered by the moving electrons in the wire.
Nuclear and Solar Energy
Nuclear potential energy - the energy stored in the nucleus of radioactive materials.Solar potential energy - the energy released by the nuclear reactions in the Sun.
Motion and Energy
Kinetic energy is the energy of a moving object.Gravitational potential energy - the energy of an object above the surface of the Earth.
Mechanical energy is the sum of the kinetic and potential energy of a situation.
Heat and Energy
Heat is the kinetic energy of the atoms in the object.ie. The hotter an object the faster its particles move. As the particles move faster the object expands.
Heat is a form of energy.
The study of the flow of heat is called thermodynamics.
Joule’s Experiments
Joule proved that heat and energy are the same. He placed a thermometer in a jar of water. Paddles in the jar stirred the water and were powered by falling masses (gravitational potential energy). By carefully measuring the change in temperature, Joule showed that energy (heat) was put into the jar by the falling masses.B2.1 Forms of Energy Review
How does heat relate to energy?
Who proved the relationship between heat and energy?
What is thermodynamics?
What type of energy do moving objects have?
Who proved the relationship between heat and energy?
What is thermodynamics?
What type of energy do moving objects have?
Practice Problems
Page 172
Knowledge 2, 3, 5, 6, 7, 10
Applications 12, 13, 14
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B2.2 Potential Energy
Potential energy – any form of stored energyGravitational potential energy - the energy of an object above the surface of the Earth.
Eg = mgh
- Eg - gravitational potential energy, J
- m - mass, kg
- g - acceleration due to gravity, 9.81 m/s2
- h - height, m
Ex. How much gravitational potential energy does a 30 kg monkey have when he is in a tree 2.0 m above the ground?
Ep = mgh
Ep = 30 kg 9.81 m/s2 2.0 m
Ep = 588.6 J
Ep = 5.9 x 102 J
Ep = 30 kg 9.81 m/s2 2.0 m
Ep = 588.6 J
Ep = 5.9 x 102 J
Ex. A mountain goat has a gravitational potential energy of 4.4 x 103 J. If the mountain goat has a mass of 30 kg, how high up the mountain is the goat?
Ep = mgh
h = Ep / (gh)
h = 4.4 x 103 J / (9.81 m/s2 x 30 kg)
h = 14.9507... m
h = 15 m
h = Ep / (gh)
h = 4.4 x 103 J / (9.81 m/s2 x 30 kg)
h = 14.9507... m
h = 15 m
B2.2 Potential Energy Review
What is gravitational potential energy?
What is the equation that describes gravitational potential energy?
What is the equation that describes gravitational potential energy?
Practice Problems
2.2 Check and Reflect page 178
Knowledge 1, 2
Applications 4 to 9
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B2.3 Kinetic Energy and Motion
Kinetic energy - the energy of a moving object.
Ek = mv2/2
- Ek - kinetic energy, J
- m - mass, kg
- v - velocity, m/s
Ex. How much kinetic energy does a car, with a mass of 1800 kg, have while traveling 90 km/h?
Ek = mv2/2
Ek = 1800 kg x (90 / 3.6 m/s)2 / 2
Ek = 562 500 J
Ek = 5.6 x 105 J
Ek = 1800 kg x (90 / 3.6 m/s)2 / 2
Ek = 562 500 J
Ek = 5.6 x 105 J
Ek = mv2/2
v = √ (2Ek / m)
v = √ (2 x 5.63 x 103 J / 50 kg)
v = 15.0066... m/s
v = 15 m/s
v = √ (2Ek / m)
v = √ (2 x 5.63 x 103 J / 50 kg)
v = 15.0066... m/s
v = 15 m/s
Do Practice Problems 4 and 5 on page 179
B2.3 Kinetic Energy and Motion Review
What is kinetic energy?
What is the equation for kinetic energy?
What affects the kinetic energy more: Doubling the mass or Doubling the velocity
Explain the answer to the previous question
What is the equation for kinetic energy?
What affects the kinetic energy more: Doubling the mass or Doubling the velocity
Explain the answer to the previous question
Practice Problems
B2.3 Check and Reflect
Application 5 to 7
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B2.4 Mechanical Energy
Mechanical Energy = kinetic energy + potential energy
Em = Ek+Eg
Em = mv2/2 + mgh
Em = Ek+Eg
Em = mv2/2 + mgh
- m - mass, kg
- v - velocity, m/s
- m - mass, kg
- g - acceleration due to gravity, 9.81 m/s2
- h - height, m
Law of Conservation of Energy
In a closed system (with no outside forces) the total amount of energy in the system remains constant.
ΣEbefore = ΣEafter
Practice Problems
Do practice problems # 8 – 12 page 183, 185
B2.4 Check and Reflect
Question 1 to 7
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B2.5 Energy Conversions
Evidence of Energy Conversions
In every energy conversion some useful energy is lost, often as heat.The more energy conversions that occur, the less efficient the system.
Energy Conversions in Natural Systems
Photosynthesis is sunlight energy changed in plants.Respiration is food energy changed in animals.
Energy Conversions in Technological Systems
Hydro-electric power stationGravitational potential energy of the water falls (kinetic energy) and is converted into electrical energy by the generator.
Eg → Ek → Ee
Coal burning power station
Chemical energy in the coal is converted to heat energy by burning. The heat is used to boil water and kinetic energy in the spinning turbine blades is converted into electrical energy in the generator.
Ec → Eh → Eh → Ek → Ee
Nuclear power station
Nuclear potential energy is used to heat water. The thermal energy is moved from one water system to another to contain radiation. Finally the hot moving water turns a generator that creates electrical energy.
En → Eh → Eh → Ek → Ee
Solar energy
Light energy causes an electric current to flow on some metals.
El → Ee
Fuel cells
Hydrogen and oxygen are combined using a special plastic membrane that conducts the electricity.
Ec → Ee
Hydrogen gas is expensive to isolate and requires energy. It is environmentally friendly only if the hydrogen can be separated without fossil fuel.