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SAM E1 Model 1
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Graphing the Forces on Atoms
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 atom is nailed down and the red atom 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 several times.
Use the "tape" controls below the model to explore the relationship between the model and the graph.
Figure out where the atoms are when the force is attractive, repulsive, and zero.
After you experiment with the model, you should be able to answer the following:
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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Distance between atoms (nm)
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<head>
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<body>
This model uses the standard tape controllers for our models. From left to
right below the model, here are the controls:
<p>
Slider. Once a model is run, you can back it up like a tape so see the
recorded images.
</p>
<p>
Reset. Restores the model to its starting condition.
</p>
<p>
Reverse. Shows the model in reverse, once it has been run.
</p>
<p>
Back step. Moves the saved model back one step.
</p>
<p>
Stop. Stops the run.
</p>
<p>
Forward step. Moves the saved model forward one step.
</p>
<p>
Run. Starts the model computing. If you forget these, you can always
place the cursor on a control and it will tell you what it does. Try it.
</p>
</body>
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<img src="Force.graph.tagged.png">
</body>
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For the graph on the left, check all the following that are true.
</body>
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There is no force at A, D, and F
There is an attractive force at D and E
There is an attractive force at A, B, and C
There is a repulsive force at D, E, and F
There is a repulsive force at A and B
There is no force at C and F
The force is essentially zero beyond F
The force is essentially zero beyond C
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