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SAM E1 Model 1
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The amount of force between two neutral atoms depends only on the distance between them.
How does the this force change at different separations?
The model below makes a graph of this force as a function of the distance between atoms.
For simplcity, the green ball is nailed down and the red ball can move in response to the force, but only in the blue area. This ensures one-dimensional motion, which simplifies the model.
Do this:
Before running the model, predict what the graph will look like.
Run the model.
Use the "tape" controls below the model to explore the relationship between the model and the graph.
Take a snapshot of the graph. (Use the camera icon in the menubar.)
Show on the snapshot regions where the atoms attracted and repelled each other.
Show on the snapshot two places where there was no force.
This model uses the standard tape controllers for our models. From left to right below the model, here are the controls:
Slider. Once a model is run, you can back it up like a tape so see the recorded images.
Reset. Restores the model to its starting condition.
Reverse. Shows the model in reverse, once it has been run.
Back step. Moves the saved model back one step.
Stop. Stops the run.
Forward step. Moves the saved model forward one step.
Run. Starts the model computing.
Some things to note:
The scientific measure of atomic distances is the nanometer (nm) which is one-billionth of a meter (10^-9 m).
The atoms in this activity are unnaturally large. We made them large so they were easy to see and manipulate.
Textbooks use different names for this force between neutral atoms. We will call it the Lennard-Jones force. It is one of several forces between atoms called van der Waals forces.
Any force that depends only on position has an associated potential energy. Let's explore the potential energy for this force.
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<b><font size="5" face="Trebuchet MS">Graphing Forces on Atoms</font></b>
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Over what range of distances is the red atom attracted to the green one?
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At about what distance between these atoms is there no force?
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