UTF-8Energy Conservation255255204
In the previous page, you learned that the total energy of two atoms stays the same. This is true unless some outside force happens to act on the atoms. This important idea is called Energy Conservation.
Is energy conserved with more than two atoms?
On this page you can find out by experimenting with a model that has any number of atoms.
The model below makes a graph the energy of any number of atoms. You should know:
The atoms are free to move.
You can add, move, and remove atoms using the three tools above the model.
As before, the net force on each atom is shown with a black arrow.
The graph shows the PE, KE, and total energy per atom.
As before, the total energy is calculated by adding KE to PE.
The x-axis is time, not separation as shown in all previous graphs.
Do this:
Use the arrow tool to move the atoms around. Note how the forces change.
Use the "Start from Rest" button to run the model with three atoms. Note how complex the motion is.
Take a snapshot of the graph of the motion of three atoms.
Show on the snapshot where on the graph the KE, PE, and total energies are greatest.
Red: KE per atom, Blue: PE per atom, Green: Total energy per atom.
Do this:
Use the third tool to add more atoms.
Run the model a few times starting with eight atoms. What do you observe?
Run the model with dozens of atoms.
Think about:
Why are there peaks on the KE graph and valleys on the PE graphs?
What about the results shows you that the total energy never changes unless you add or remove KE?
The amazing thing is that the total energy stays constant if you leave it alone. Energy Conservation applies to any number of atoms.
Some of your observations hold true for hundreds of atoms. In the next activity, you can explore models with up to 500 atoms.
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<b><font size="5" face="Trebuchet MS"> Energy Conservation</font></b>
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</html>-243f9a757516true75.075.01416255 0 014255 0 0true16255 0 0truetrue75.075.0true75.075.0Trebuchet MS18truetrue75.075.075.075.01475.075.01475.075.01475.095.0org.concord.modeler.text.BulletIcon$SquareBulletIcon141475.095.0org.concord.modeler.text.BulletIcon$SquareBulletIcon141475.095.0org.concord.modeler.text.BulletIcon$SquareBulletIcon141475.095.0org.concord.modeler.text.BulletIcon$SquareBulletIcon141475.095.0org.concord.modeler.text.BulletIcon$SquareBulletIcon141475.095.0org.concord.modeler.text.BulletIcon$SquareBulletIcon141475.075.01475.075.014true1475.095.0org.concord.modeler.text.BulletIcon$SquareBulletIcon1414selectObject.gif141475.095.0org.concord.modeler.text.BulletIcon$SquareBulletIcon141475.095.0org.concord.modeler.text.BulletIcon$SquareBulletIcon141475.095.0org.concord.modeler.text.BulletIcon$SquareBulletIcon141475.075.075.075.01org.concord.mw2d.activity.AtomContainerpage8$0.mmlfalseorg.concord.modeler.PageXYGraph0Time (fs)Kinetic Energy/ParticlePotential Energy/ParticleTotal Energy/Particlefalse0.020000.0false-1.00.7300250Time (fs)Energy (eV)true420450-333301-1falseRaised Bevel75.075.075.075.01255 0 0truetrue0 0 255truetrue0 153 51truetrue75.075.075.075.01org.concord.modeler.PageButton<html><b><font size=3>Reset</html>Restart the model and graph7028falseorg.concord.mw2d.models.MolecularModel0Execute MW scriptorg.concord.modeler.PageButton<html><b><font size=3>Start from Rest</html>13028falseorg.concord.mw2d.models.MolecularModel0Execute MW scriptorg.concord.modeler.PageButton<html><b><font size=3>Add KE</html>Add kinetic energy to all atoms9028falseorg.concord.mw2d.models.MolecularModel0trueExecute MW script75.075.075.075.014true1475.095.0org.concord.modeler.text.BulletIcon$SquareBulletIcon141475.095.0org.concord.modeler.text.BulletIcon$SquareBulletIcon141475.095.0org.concord.modeler.text.BulletIcon$SquareBulletIcon141475.075.01475.075.014true1475.095.0org.concord.modeler.text.BulletIcon$SquareBulletIcon141475.095.0org.concord.modeler.text.BulletIcon$SquareBulletIcon141475.075.075.075.01416255 0 0true1475.075.075.075.0org.concord.modeler.ImageQuestion400250Raised Bevel<html><font face="Verdana" size="4">Insert here a snapshot of a graph for a system with eight atoms that has <b>negative</b> total energy. In the caption, explain how this is possible. </font></html>org.concord.modeler.ActivityButtonHint 1Hint about how to get negative PEfalseThink about the separation of two atoms that gives negative PE.Hintorg.concord.modeler.ActivityButtonHint 2Hint about how to position atoms for negative PE.falseIf atoms are close but the force is small, their PE is negative. Start the model with many atoms positioned so that they are close and the force on each is small. Hint75.075.0org.concord.modeler.ImageQuestion400250Lowered Etched<html><font face="Verdana" size="4">Insert here a snapshot of a graph for a system with eight atoms that has <b>positive</b> total energy. In the caption, explain how you created this model. </font></html>org.concord.modeler.ActivityButtonHint 1Hint about how to start the modelfalseYou cannot get a positive energy if you start the atoms at rest. PE is never positive and at rest KE is zero, so their sum will always be zero or negative. Hintorg.concord.modeler.ActivityButtonHint 2Hint about how to start the modelfalseStart the model and use the button that adds KE. Hint75.075.075.075.01414255 0 014255 0 0true14255 0 01org.concord.modeler.text.LineIcon40101010<html><body face="Trebuchet MS">
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