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SAM E1 Model 1
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The Potential and Kinetic Energy of Atoms
Kinetic energy is the energy of motion.
Potential energy is the energy of position.
How do these two energies relate?
If you throw a ball upward, it slows down as it rises, which means that it looses kinetic energy. But because it gains height, it increases its potential energy.
On the way down, the ball speeds up gaining KE, but looses PE. If you neglect friction, the total energy remains constant--the KE and PE change, but their sum remains the same.
The same holds for an atom. As it loses PE, it gains KE in equal measure. As it looses KE, it gains the same about of PE.
Potential energy is a very powerful concept. It provides a shortcut for solving problems and leads to deeper understanding of complex systems.
Use the following model to explore how KE and PE relate.
The model below makes a graph of both the PE and KE of the red atom.
Once again, the green ball is nailed down and the red ball has to move in the blue area.
Do this:
Before running the model, predict what the two curves (PE and KE) will look like.
Run the model.
Use the "tape" controls below the model to explore the relationship between the model and the graphs.
Take a snapshot of the graph. (Use the camera icon in the menubar.)
Show on the snapshot where on the graph the atom is moving fastest and where it stops.
Red: Kinetic Energy
Blue: Potential Energy
The total energy is just the sum of KE and PE. What do you predict for the total energy for these two atoms?
The next page explores this question.
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Why does the KE increase as the red atoms moves to the right?
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As the red atom moves to the right, there is an attractive force to the right. This increases the speed of the atom, which increases its KE.
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How does the "High Speed Start" change the PE and KE graphs?
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The high speed start gives the red atom a starting KE, so its graph is lifted up.
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