Click the mouse button on the pendulum weight and drag it to any position you wish, to start it. Then click on action to see the pendulum motion and a display of the total, radial and tangential acceleration vectors. The total acceleration is in the cyan color, the radial acceleration is in the green color and the tangential acceleration is in the red color.
You may have noticed that the pendulum display has some features not seen before. This display allows you to not only look at the pendulum in real space but also to see position and velocity as functions of time and to see some other plots called the phase space projection and the phase space orbit. This display was borrowed from another program and rather than hide these novel features, I left them available so that you might be intrigued. If you have questions, refer to the "Order - A closer look at chaos" section of the School of the Web.