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SAM E1 Model 1
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The Total Energy of Atoms
The total energy is the sum of KE and PE.
Can you estimate the total energy for two atoms?
The model below makes a graph of the PE, KE, and total energy 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 three curves (KE, PE, and total energy) will look like.
Run the model.
Use the "tape" controls below the model to explore the relationship between the model and the graphs.
By changing the starting positions and using the two buttons, obtain graphs that look approximately like each of the following.
Super Challenge:
So far, we have looked at only one pair of atoms. What happens when there are more?
The next activity let's you experiment with three or more atoms.
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<html>
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<body>
Use the graph this to compute the total energy at different distances
between atoms.
<p>
For instance at 0.6 nm the PE (the blue curve) is about –0.6 eV and the
KE is about 0.6 eV. What is the sum of these two?
</p>
<p>
Repeat this calculation when the distance is 0.8, 0.9, and 1.0 nm.
</p>
</body>
</html>
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<img src="Annotated.graph.png">
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org.concord.modeler.ImageQuestion250300Lowered Etched
Place your annotated graph here.
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What is the total energy at 0.7, 0.8, 0.9, and 1.0 nm?
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Zero. Always.
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<html>
Explain why the red atom can move, even if it has zero total energy.
</html>
Potential energy become negative as the two atoms attract. This makes it possible to have positive kinetic energy while their sum is zero.
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Energy (eV)
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Raised Bevel
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<html>
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<body>
<p>
</p>
<p>
</p>
<p>
Red: KE of the red atom
</p>
<p>
Blue: PE of the red atom
</p>
<p>
Green: Total energy of the red atom
</p>
</body>
</html>
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org.concord.modeler.PageButton
<html><b><font size=3>Start from Rest</html>
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<html><b><font size=3>High Speed Start</html>
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<html><b><font size=3>Reset</html>
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Execute MW script
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Negative.tot.energy.png
Positive.tot.energy.png
Zero.tot.energy.png
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<html>
How much does the total energy change during a run?
</html>
It stays constant. It does not change.
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<html>
Describe the motion of the red atom when the total energy is negative.
</html>
It is trapped!
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<html>
Describe the motion of the red atom when the total energy is positive.
</html>
It is free to move about the container.
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Can you make the graph at right?
The model started with the red atom trapped at rest 6 A from the green one. Using the "High Seed Start" button, the red atom eventually got free. How was it done?
</html>
Press the "High Speed Start" each time the red ball has traveled as far as it can to the left. Repeat seven times.
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<img src="Super.Challenge.png">
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org.concord.modeler.ActivityButton
Hint
It is like pushing a swing. You have to push at the right part of the swing.
Hint
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