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E1 Summary
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[The following are not yet complete. RT]
Indicate on the following force graphs where the force is a) toward the left, b) toward the right, and c) zero.
Indicate on the following potential energy graphs where the force is a) toward the left, b) toward the right, and c) zero.
One atom is at rest and another hits it. Sketch a graph of the forces, kinetic energy, potential energy, and total energy as the two atoms interact.
If the MW sometimes makes errors, how can we learn anything from it?
Is a MW model accurate if it predicts energy conservation?
The following is a graph of KE and PE of a safe being dropped off the top of a building. Where on the graph was the safe a) at the top of the building, b) mid-way down, c) at the ground. Estmate the graph of the total energy. Is energy conserved?
Many energy conversions in the lab do not conserve energy because energy is lost as heat. Give some examples. Does this happen at the atomic scale?
(For quantitative treatment) Estimate the force required to pull a crystal apart.
**At room temperature, the average atom has a KE of about 1/40 of an electron volt. The mass of a helium atom is 3.3*10^–27 kg; how fast is it going? Hint, solve KE = (1/2)mv^2 for v and plug in values in kg and Joules for mass and KE.
Challenges
0. Run a MW model and use the pause, stop, rewind, step, and trace buttons to obtain and accurately annotate a snapshot a particular interaction.
0. Arrange and run a model to find out how the shape of the potential energy between two atoms influences their motions.
0. Set up and run a model that represents a gas, liquid, or solid.
0. Identify which of two models contains atoms with stronger attractions.
0. Design, set up, and run a system of several interacting atoms and determine whether their total energy is conserved.
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<b><font size="5" face="Trebuchet MS">Summary Questions</font></b>
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1. Describe the general shape of the Lennard-Jones force. What is the force when atoms are a few diameters apart? When they almost touch?
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2. Describe the general shape of the Lennard-Jones potential. What is the potential when atoms are a few diameters apart? When they almost touch?
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3. Is it possible to have negative kinetic energy? Why?
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4. Is it possible to have negative potential kinetic energy? Why?
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5. If the KE and PE of an isolated system can change, how can the total energy stay constant?
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As one increases, the other decreases by the same amount.
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6. Helium is about the simplest natural element. It consists of light atoms that do not react. If you get it cold enough, it forms a liquid. Why do liquid helium atoms stick together and not fly apart?
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