| Pendulum & Ball (Calibration Lab): You can place two of these pendulums. Attach one to the vertical Scale to see how much a pendulum ball weighs. From this weight, you can determine its mass. You must click on the Scale to attach the pendulum. This pendulum ticks like a clock, but that has no significance. Attach the second pendulum to the Protractor. You can click anywhere in the simulator to attach the pendulum. Then you need to attach the pendulum to the horizontal scale on the cart (see illustration below). The pendulum in the Coulomb lab has a separate help page. To attach the pendulum to the scale on the cart, first select the pendulum. Click on the string loop under the pendulum ball (Figure 1 below) and drag it to the hook on the scale (Figure 2). Make sure the loop is exactly on the hook, just as shown in Figure 2. Release the mouse. Hopefully, the string will be connected to the scale. If it drops back down, try to attach the string to the scale again.
Fig. 1 | Fig. 2
Fig. 3 | Fig. 4
To measure the horizontal component of the Coulomb force acting on the pendulum ball, move the cart to the right until the string connecting the scale and the ball is perfectly horizontal (Figure 3 above). In Figure 3, the angle measured by the protractor is 31º and the force measured by the scale is 0.6 mN. If the angle measured by the Protractor matches the angle in the Coulomb lab, then the tension in the string equals the Coulomb force acting on the ball. In order to get the angles to match, most of the time you will need to move the Platform that supports the cart. To accomplish this, click on and drag the Platform up or down, or select the Platform and use the up and down arrow keys. Then adjust the cart's position. In Figure 4, the Platform has been lowered. The measured angle is 10º and the measured force is 0.17 mN.