Today we did our first lab with the air track and glider. The air track works just like an air hockey table, it has little holes all over the track so the glider floats on the air coming out of the holes, eliminating friction (for the most part). Students used the Video Physics App on the their iPads to record a movie of the glider moving along the track
We put a tiny bright yellow sticker on the glider (as seen on the first photo) to make it easier to track the glider. After you take the video you go frame by frame of the movie and mark the position of the glider by putting the cross hairs on the yellow sticker. Apparently the app had an update since the last time we used it because one of the students noticed a wonderful little button labeled track in the bottom right corner of the screen. If you hit this button after labeling a few data points the app goes through the rest of the movie and attempts to label all your data points! This is a great time saver and worked really well. There was only one data set where the app had a few problems, but you can go back and manually mark those data points.
Once you have all your data points marked, you have to set the scale and origin (location of x=0, y=0). The scale was easy since the glider has centimeters marked on its side, we just moved the two big circles you see on the photo below, so they were 10 cm apart and entered that in the box above the glider. To set the origin you just drag the origin, where X and Y cross, to where you want it. You can rotate it as well so if your movie wasn’t exactly level you can tilt the axes to match up with your surface, in our case the air track. Tapping on the graph icon in the top right corner of the app (not shown in pictures) shows you a graph of position (x) versus time (t) and velocity along x versus time. It will also show you graphs for the y axis but we don’t need them for this experiment since all the motion is in 1 dimension along x.
You can see that the data makes a beautiful line, which indicates the position changed at a constant rate, i.e., that the velocity of the cart was constant, until it hit the end of the track and reversed direction. While these graphs are very nice, I wanted to make sure the kids knew how to graph data and draw the best line through their data, so they had to print out their data and graph some of it by hand. After drawing a line through their data points they found the slope and hence the velocity of the cart. They then compared that answer to the one the app gave and they were the same.
I won’t always make them graph their data by hand but its a useful and necessary skill if you plan on continuing in science. This lab could be done with a marble in a straight track, matchbox car on the floor (though these tend to have quite a bit of friction), any toy that moves at constant speed.