sciencegeekgirl » Hands on Science Sunday: Ticker-tape timer for measuring motion

picture copyright Don Rathjen of Exploratorium

A pretty standard lab for introductory physics is to chart what constant speed (or constant acceleration) looks like, and graph it versus time. There are all different ways to do this, but one is to use a ticker-tape timer, which I think is wonderfully cool. The idea is to attach a piece of ticker tape to whatever object you want to graph the speed of, and then have some apparatus (a ticker tape timer) that makes marks on the ticker tape at regular time intervals. If the ticker-tape timer made a mark every second (which would be convenient), then the distance between marks on the ticker tape would represent the distance traveled per second. Generally they’re much faster, and timer speeds are measured in hertz. Whatever the units, though, you now have a graphical representation of distance per time!

To make a graph, you can then cut up the ticker tape. Choose a unit of time that you want to use on your x-axis — for example, 10 “hits” of the ticker tape timer. That will be the unit of time. (It’s generally arbitrary, since the timer doesn’t hit every second). Chop your marked ticker-tape into 10-mark sections. The horizontal axis, then, is time, and the vertical is distance per unit time.

If it was moving at constant acceleration, it will look like this:

If it sped up and then slowed down it will look like this:

All images are taken from the Practical Physics website, which has a lot of experiments using ticker-timers. Go to their experiments website and search for “ticker” to see labs on measuring time, velocity, and other aspects of motion.

Of course, what is this “ticker timer” that will actually make the marks for you? If you’re a tinkerer, there is a wonderful write-up for a DIY ticker timer from the Exploratorium (PDF) by Don Rathjen. It’s a fussy thing to make, though, so really only for the type of person who reads those detailed instructions and thinks “Hey, I want to make that!” (and if you are, you’ll love Don’s instructions for making a clock escapement). Still, I recommend downloading the instructions, because they give some really cool examples of how you can use these, including how to make displacement and acceleration graphs (instead of just velocity graphs) and how to measure “g”.

If you have the money, though, Arbor does sell (for $140) a spark timer that does the same thing. Here is their ticker-timer lab (written for advanced and introductory levels) with links to all the needed materials.

Useful for all sorts of things, they also sell cheap constant acceleration cars and constant velocity cars. (New, improved! It actually goes straight!).

And, if you really need it to be on the cheap, there are some online applets for constant velocity and constant acceleration that were recommended by a physics teacher.