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Natural Science - Year II

Unit 46: James Watt and Steam Power

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Science Web Assignment for Unit 46

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Science Lecture for Unit 46: Heat and Energy

For Class


Science Topic: Thermodynamics and Energy

Forms of Energy

During the seventeenth and eighteenth centuries, scientists begin to distinguish different forms of energy.

Study the conversion of energy diagram.

  • How is energy of position (potential energy) converted to heat and sound?
  • How is chemical bond energy converted to electrical energy?
  • How is chemical bond energy converted to heat energy?
  • How is light energy converted to chemical bond energy?
  • Which forms of energy involve moving objects around in a force field (changing potential energy)?
  • Which forms of energy involve putting objects into motion (kinetic energy)?

Energy can change from one form to another. When we lift a book ont a shelf, moving it further from the center of the earth, we exert our own force of lifting against the gravitational forces attracting the book to the earth. The work we do is equal to the force (mass m * acceleration due to gravity g) times the distance d we move the book:

Work W = potential energy change ΔPE = force F * distance moved d = mgh

When we take the book off the shelf and let go, the force of gravity is no longer facing resistance by the shelf, and the book falls, expending kinetic energy ½mv2, with increasing velocity until it hits the floor.

Work W = potential energy change ΔPE = force F * distance moved d = mgh = energy recovered when book falls = ½mv2

(In this case, v is the average velocity over the course of the fall, since the book starts with 0 velocity if we just drop it.)

The fact that we can change one form of energy into another makes most of modern technology possible. The steam engine is a mechanism to change heat energy to mechanical energy, and to direct that mechanical energy so that it will do useful work, that is, what we want it to do. A photocell is a way of changing radiation or light energy into electrical energy or current.

The underlying rules of changing forms of energy come from the study of heat as an energy source used to do work, or thermodynamics. One of the most important intellectual advances in science during the 19th century was the realization that heat is a form of kinetic energy--the energy of many many atoms and molecules in motion. Heat energy can flow from one substance to another in one of three ways:

A good example of the three forms of heat transfer is a pot of boiling water on an electrical stove. The burner heats up and begins to glow -- that's radiation. Using conduction, the bottom of the pan in contact with the burner begins to heat up by conduction: the molecules in the burner move and transfer energy to the molecules in the pan's bottom surface, which transfer energy to the molecules of water along the inside surface of the pan. Using convection, water molecules heated up along the surface of the pan move away from the surface and carry their energy to the center of the volume of water.

Work through the presentaion on Heat Transfer at Fox Valley Technical College, WI.

  • Which forms of heat transfer require something to move?
  • Which forms of heat transfer can work across a vacuum?
  • Which forms of heat transfer require contact between objects of different temperatures?
  • It is impossible to follow every atom through every motion, but using statistical methods, scientists could predict probable outcomes of different situations. As we'll see in a later unit, the statistical analysis lead to studies of how many states a give system can have. Some of the states we would consider ordered (the members in a particular symmetrical distribution, for example), more states are unordered or randomly distributed. So the likelihood of winding up in an ordered state is less than the probability of ending up in a disordered state.

    Study/Discussion Questions

    Further Study On your Own (Optional)