| Graph Tool: The Graph Tool plots two variables against each other dynamically. It functions in both Run mode and Stop mode. You must select the variables to be plotted. Place up to ten graph tools anywhere in the simulation window. With Select depressed, you can move and resize the graph tool in Stop mode. In the graph tool's Properties Box, you can set a wide variety of properties. These properties are discussed in detail under the topic headings listed below. Click on the topic of interest.
What Can I Plot? | Choosing Scale Mode | Setting Axis Variables & Scales
Miscellaneous Properties | Rises and Runs | Graph Example
What Can I Plot?
Microscopic Pressure | Ideal Gas | Gas Diffusion
Evaporation | Freezing and Melting | Gas Simulator

In the Microscopic Pressure Simulator, you can plot:

- Time, if the clock has been placed. The default scale label for time is sec.
- Collisions per second, if a collisions per second meter has been placed. The default scale label is collisions/sec.
- Impulse per collision, if an impulse per collision meter has been placed. The default scale label is impulse/collision.
- Total force, if a total force meter has been placed. The default scale label is Total Force.

In the Ideal Gas Simulator and Gas Simulator, you can plot:

- Time, if the clock has been placed. The default scale label for time is sec.
- Pressure, if a pressure meter has been placed. The default scale label is atm.
- Volume, if a volume meter has been placed. The default scale label is liters.
- Temperature, if a temperature meter has been placed. The default scale label is Kelvin or Celsius.
- Density, if a density meter has been placed. The default scale label is grams/liter.
- Number density, if a number density meter has been placed. The default scale label is # particles.
- Impulse per collision, if an impulse per collision meter has been placed. The default scale label is impulse/collision.
- Average particle speed, if a speed/energy meter has been placed and speed selected. The default scale label is m/s.
- Average particle energy, if a speed/energy meter has been placed and energy selected. The default scale label is meV (milli-electron volts).

In the Gas Diffusion Simulator, you can plot:

- Time, if the clock has been placed. The default scale label for time is sec.
- Pressure, if a pressure meter has been placed. The default scale label is atm.
- Density, if a density meter has been placed. The default scale label is grams/liter.
- Number density, if a number density meter has been placed. The default scale label is # particles.
- Impulse per collision, if an impulse per collision meter has been placed. The default scale label is impulse/collision.
- Average particle speed, if a speed/energy meter has been placed and speed selected. The default scale label is m/s.
- Average particle energy, if a speed/energy meter has been placed and energy selected. The default scale label is meV (milli-electron volts).

In the Evaporation Simulator, you can plot:

- Time, if the clock has been placed. The default scale label for time is sec.
- Pressure, if a pressure meter has been placed. The default scale label is atm.
- Temperature, if a temperature meter has been placed. The default scale label is Kelvin or Celsius.
- Density, if a density meter has been placed. The default scale label is grams/liter.
- Number density, if a number density meter has been placed. The default scale label is # particles.
- Average particle speed, if a speed/energy meter has been placed and speed selected. The default scale label is m/s.
- Average particle energy, if a speed/energy meter has been placed and energy selected. The default scale label is meV (milli-electron volts).
- Particle sticking rate (sticking to liquid surface), if a sticking rate meter has been placed and energy selected. The default scale label is # stick/sec.
- Particle leaving rate (leaving liquid surface), if a leaving rate meter has been placed and energy selected. The default scale label is # leave/sec.

In the Freezing and Melting Simulator, you can plot:

- Time, if the clock has been placed. The default scale label for time is sec.
- Volume, if a volume meter has been placed. The default scale label is liters.
- Temperature, if a temperature meter has been placed. The default scale label is Kelvin or Celsius.
- Density, if a density meter has been placed. The default scale label is grams/liter. This is an error, because the meter actually measures kilograms/liter. You should reset the scale label accordingly.
- Number density, if a number density meter has been placed. The default scale label is # particles.
- Average particle speed, if a speed/energy meter has been placed and speed selected. The default scale label is m/s.
- Average particle energy, if a speed/energy meter has been placed and energy selected. The default scale label is meV (milli-electron volts).

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Scale Mode: Before you choose variables, you should decide which Scale Mode to use. If you choose Auto Scale Mode, the simulator chooses the axis scales for you. If you choose Hand Scale Mode, you must set the axis scales yourself.

We suggest that if you know what range of values will be plotted, or can make an educated guess, choose Hand Mode. You will generate a better-looking graph that is easier to interpret than one drawn in Auto Mode.

If you don't know what range of values will be plotted, choose Auto Mode. Once the graph has been generated, you will know the range of values. Most of the time, you can then replot the graph in Hand Mode.

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Axis Variables: Choose the Vertical and Horizontal variables to be plotted from among those listed in the pull-down menus. See What Can I Plot? to find out which variables you can plot and how to get them to those variables to appear on the pull-down menus.

Scaling the Axes (Hand Mode ONLY [see Scale Mode]): Set the following properties for each axis:

- Begin value: The minimum axis value at the graph's origin.
- Step value: The distance between each notch on the axis in units of the variable being plotted. This value must be positive.
- Step size: The size of each step, in pixels. The default value is 20. The minimum step size is 10 pixels and the maximum is 50 pixels.
  The maximum graph size is approximately 200 X 200 pixels. Thus, the axis end value ( maximum axis value) for a graph of maximum size is:
  end value = begin value + (step value x [200 pixels / step size])
- Scale label: The label indicating the units of the axis variable. In most circumstances, the default label displays the correct units. See What Can I Plot? to find out what the defaults are.

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Miscellaneous properties.

Options

- Show marker: Show the marker that traces the plot.
- Clear graphic: Clear the graph when you click Apply or OK.
- Dynamic scaling: Auto Mode only. If chosen, the graph automatically redraws itself when the marker moves off the graph. Leave this box checked.

Refresh time: How often the graph tool draws a new point. In most circumstances, you will want the shortest time--100 ms, or 0.1 seconds. This is the default value.

Step precision: The precision with which the graph tool determines step values. If you have a step value less than 1, choose a step precision of 3.

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Rises and Runs properties: The Rises and Runs feature lets students use a triangular approximation to determine the rate at which the vertical variable is changing with respect to the horizontal variable. For example, if the graph tool is plotting velocity against time, the Rises and Runs feature lets students approximate the acceleration.

The Rises and Runs feature only works if the vertical variable increases or decreases monotonically with respect to the horizontal variable. If changes are not monotonic, the simulator informs the user that the Rises and Runs feature does not work. Then it turns off the Rises and Runs feature.

Rises and Runs: Turns on the Rises and Runs feature.

Shade segments: Shade regions under the curve formed by each "rise" and "run."

Number of segments: Number of rises and runs.

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In the figure to the right, the graph tool plots density (the vertical variable) against time (the horizontal variable). For density, the begin value is 0, the step value is 0.1, and the step size is 20 pixels. For time, the the begin value is 0, the step value is 10, and the step size is 20 pixels. In the top right corner, clicking on the C in Select clears the graph. Rolling the mouse over the dot turns the graph on or off. The graph is on when the dot is red and off when the dot is black. The silver-gray sliders on the left and botton of the graph allow you to adjust the horizontal and vertical scales of the graph, but only in Stop mode and only if you chose Hand Mode. In Run mode, the scales revert to the values specified in the Properties Box. |

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