Determine the relationship between force and acceleration for constant mass. 1. You will need a digital watch/clock that shows seconds, preferably tenths of seconds (a stopwatch or the stopwatch setting on a digital watch would be best). Go to PHET Forces and Basic Motion simulation (https://phet.colorado.edu/en/simulation/forces-and-motion-basics). You should be able to click on the arrow in the middle of the display to run it, or, if you want, you can download it onto your computer