This display is a 2 dimensional free body diagram tool. You may enter the effective mass of the particle, the initial position, the initial velocity if any and a series of force vectors. The program resolves the force vectors, calculates the accelerations and plots the trajectory of the particle. We are limited to forces that are constant over time at this stage. Later we will add the ability to deal with forces that may depend on time or some other parameter.

There are two different views on this display. One is the free body diagram, the other is the plot of positions vs time. The display opens with the free body diagram view where you may enter values for the following parameters in addition to the normal space cell limits:

Effective mass (mass)

Initial x position (ix)

Initial y position (iy)

Initial velocity magnitude (|iv|)

Initial velocity angle (iv angle)

Force magnitude (|f|)

Force angle (f angle)

The force magnitude and angle input pairs may be repeated for up to 10 different force vectors. Changes to the initial position adjusts the space cell limits to keep the particle centered. Setting the initial velocity requires both magnitude and angle to be set. When that is done, a vector in gray shows the direction of the velocity. This vector may not be to scale since the scale is set up based on force vectors. The x and y components of all vectors are displayed on the screen. You may edit a force vector already entered by clicking on the screen where the text describing the vector is located. In addition to the x and y position which are always shown, you may choose to plot the velocity components and speed. Check the appropriate check boxes. When the free body diagram is complete, click on the Plot button to display the time plot view. If you want to edit a force value that you hsave already locked in, just click on that force in the list at the upper left of the drawing area.

In the time plot view you may change the amount of time displayed by entering a value in the horizontal limit input box. The vertical scale of the time plot is set automatically so the other space cell limits are locked in. By positioning the cursor you may pick off values of time, x position or y position in which you are interested. Clicking on FBD when the time plot is shown will toggle the free body diagram back up so you can review the parameters or add additional force vectors. The reset button restores all default values and sets up the free body diagram view.

As an example, on the free body diagram below enter an initial velocity magnitude of 10 meters per second at an angle of 45 degrees. Then enter a single force of 9.8 Newtons at an angle of -90 degrees. This represents a situation like the ball toss with both vertical and horizontal velocity. Find the maximum height to which the particle rises and the time at which that height is reached. We will work additional examples using the free body diagram later.