The directions were pretty simple--predict exactly where a ball will land after rolling off a table. Do this by catching it in a can on the first try.
The sum total of my written directions:
We crashed the physics lab for the long tables and cobbled together some ramps and a track for a ball using meter sticks and masking tape.
I don't have any fancy meters and such to measure horizontal velocity of the ball after it comes off the ramp. Instead, I had students use their phones to video trial runs of the ball down the ramp. If the ball conveniently fell of the table and hit the floor I threatened to dock their group a grade on the experiment. That was probably an empty threat but it worked--no one cheated by testing where the ball would hit the ground.
In order to measure the horizontal velocity of the the ball, we need to have distance over time. We'll get the time portion based on the number of frames in the video (30 frames per second). To make sure we get good measurements, I had students place masking tape perpendicular to their ramp at a set interval. We would measure the speed of the ball over that distance.
In order to measure the horizontal velocity of the the ball, we need to have distance over time. We'll get the time portion based on the number of frames in the video (30 frames per second). To make sure we get good measurements, I had students place masking tape perpendicular to their ramp at a set interval. We would measure the speed of the ball over that distance.
Enter a brilliant little freeware program called Physics Tracker. Here's a write up of it I did for a technology conference.
Plug in the phone into the computer. Download the video file. Now your ready to go. There are two different ways to find a speed using the Tracker software. First, the easy way. The Tracker software advances video files one frame at a time. Because standard video is 30 frames per second, this gives us a rate we can use for our calculations. Find the number of frames it takes to travel the set distance between the pieces of masking tape then divide by 30 to get your horizontal velocity: distance/#frames * 30frames/1second = distance/#seconds.
The second way actually uses the tracking portion of the software--hence Physics "Tracker". It's pretty neat but takes longer to explain. If your interested, here's the link.
Plug in the phone into the computer. Download the video file. Now your ready to go. There are two different ways to find a speed using the Tracker software. First, the easy way. The Tracker software advances video files one frame at a time. Because standard video is 30 frames per second, this gives us a rate we can use for our calculations. Find the number of frames it takes to travel the set distance between the pieces of masking tape then divide by 30 to get your horizontal velocity: distance/#frames * 30frames/1second = distance/#seconds.
The second way actually uses the tracking portion of the software--hence Physics "Tracker". It's pretty neat but takes longer to explain. If your interested, here's the link.
Students now need to figure out how long it will take for the ball to hit the ground. I didn't give any help on this one in Algebra 2 or Physics. We've done enough free-fall objects with acceleration of 9.81 m/s^2 that I dodged all pleas for help. After figuring out the number of seconds, the horizontal equation is just distance = rate*time.
Students measured off from the end of the table (not the base) and placed the can on the ground. The air was tense; grades were riding on the accuracy of their calculations and measurements. It turns out no one needed to worry.
Students measured off from the end of the table (not the base) and placed the can on the ground. The air was tense; grades were riding on the accuracy of their calculations and measurements. It turns out no one needed to worry.
We started with the target requirement being a coffee-sized can. I found this strange looking can in the back of my closet so we used it. Waste not want not. Every group easily made it into the target can. They were super stoked. I was curious: how small could we actually go?
So, we changed the target to a soup-sized can. Again, whatever I found in my closet. I think this was actually a bit smaller than a soup can. The groups had to recheck some calculations because the height of the target had changed. Here's the video results:
Having done all sorts of quadratic experiments, I would definitely do this again. For comparison, I probably will not do the m&m catapult again--the math objectives got lost in the sloppy measurements.
Have fun!
Have fun!
RSS Feed
