Algodoo

This uses script to calculate the velocity of a wheel. Run the wheel by checking "Motor" in the window on the right. If you change the wheel size, you must define its diameter by setting scene.my.dr in the console.
See at the script on the green, brown and cyan boxes. The small circle near the green box is the trigger for refreshing the display. The cyan box is the timer starter and the brown box is the timer checker and speed calculator. The function Round has been defined by the console.