Tag Archives: demonstration

Video Analysis of a Bouncing Ball


Nothing earth-shattering here. I just wanted to share the activity we worked on today, which was an introduction to quantitative energy conservation by doing a video analysis of a bouncing ball. (Up until now, we were only doing qualitative energy pie charts.) Here are the handouts and the video:

The graphs from the analysis are just beautiful:

HeightTime VelocityTIme EnergyTime

Lots to talk about in those graphs!

Feel free to edit and reuse the handouts as you see fit. They’re not perfect, but I figure it’s better to share them than having them collect dust on my flash drive.

PS: I’ll sheepishly admit that I don’t do the whole suite of paradigm labs in the Modeling unit to mathematically derive the energy equations from experiments. But we do some simple qualitative demos/experiments to discover what variables would be in those energy equations. We start by talking about how the further a rubber band is stretched, the more energy it stores. Then we launch carts into a rubber band “bumper” (i.e., big rubber bands from Staples and two C-clamps) to qualitatively see the energy stored.

In doing so, we see that the cart’s kinetic energy depends on its speed and its mass. (Or is it weight? What would happen if we repeated the experiment on the moon?)

For gravitational energy, we can repeat the experiment, but have carts rolling down an incline. Or use the rubber band to launch the cart up the incline. I’ve also dropped balls into sand and looked at the depth to which they get buried. Either way, we see that gravitational energy depends on height and weight. (Or is it simply mass? What would happen on the moon?)

For elastic energy, we already know it depends on the distance the rubber band is stretched. Then, we can swap out the rubber band in the bumper with a stiffer/looser one to see the effects of the spring constant on energy stored.

Then, after we predict what the energy equations might look like, I just give them the actual energy equations, or have them look them up. (Gasp! See Schwartz’s A Time for Telling, aka Preparation for Future Learning.)

So, modelers, what am I missing by not doing the full-blown energy paradigm labs? How do you introduce the quantitative energy equations?

Newton’s 3rd Law (or How to Make Effective Use of Video for Instruction)

Exhibit A:

Exhibit B:
Download the high-quality video clips for each collision.


Increasing Engagement in Science

As part of a session on innovative practices in science at TeachMeet New Jersey 2011, I gave a presentation entitled “Tips, Tools, and Techniques for Increasing Engagement in Science”

I have posted that presentation, complete with speaker’s notes and plenty of links to further information, here: http://bit.ly/EngageSci

Any feedback you have would be greatly appreciated! (e.g., is there a bigger theme I am missing, etc.) Thanks! J3BC3J3HSY8J

I Love JayCut

Action-Reaction isn’t turning into an edtech blog, I promise. However, my students and I have been using JayCut (a free, online video editor) to create video lab reports and video demonstrations from clips taken with our Flipcams.

One nice feature that has great potential is JayCut’s picture-in-picture. It started when I saw this awesome video taken from the point of view of the edge of a sword:

I thought, wouldn’t it be cool if there was a 3rd-person perspective synced up with the sword’s perspective? So I set out to create my own version using a Flipcam and a meter stick (not as cool as a sword, I know). I had a student use a second Flipcam to film me while I swung the “sword” around. We made sure we pressed the record buttons at the same time. Then I used JayCut to merge the two videos together. Here’s the result:

The picture-in-picture effect is really just a transition, but I made the transition last for the duration of both video clips, rather than having one clip transition to the other. In addition, you can see that JayCut allows you to add titles, still photos, and upload your own audio.

Do you remember my Visualizing Newton’s 3rd Law with Colliding Carts post a while back? Well, I just discovered that JayCut can also do variable playback speed. So today I merged the 4 videos from the post (plus 1 extra) and included slow-motion replays so you can see that both hoops are always equally compressed. Check it out:

(FYI: I snagged the royalty-free audio for both of my videos from Kevin MacLeod at incompetech.com.)

My students have also been experimenting with video lab reports. Here’s an example from an activity about shoes, friction, and tug-of-war:

I know this group’s experimental design can be improved, but I wanted you to see some actual student work. Doing a video was a choice — other groups wrote a more traditional report or presented to the class using whiteboards.

When your movie is complete in JayCut, you can publish the video to YouTube, publish it to JayCut’s own site, or download the file to your computer. You can also get an embed code to put the video into a webpage, blog, etc. without publishing to YouTube.  (I find the YouTube version to be higher quality, though.) When my students made video lab reports, they got the embed code and put their video on our private Edmodo class page.

JayCut will store all the clips, stills, audio, etc. you upload into your media library so you can use them over and over again. You can save your work and finish later. I don’t know of any file size limit or storage limit. I really can’t believe the site is free, and there’s also no advertising. You do have to sign up for an account, but I have not received any email or spam from JayCut.

That’s it. I just wanted to show everyone what JayCut can do!

(NOTE: Some media in this post may not display in feed readers and must be viewed on the website.)

15 Ideas for Using Digital Cameras in Science

1. Stop motion movies and flip books.

By taking multiple pictures, students would create a photo flip book or stop motion movie to demonstrate, as accurately as possible, a particular science concept or process. For some examples, see Dale Basler’s post Create stop-motion videos and learn physics. Another way to easily create stopmotion films is with SAM Animation software (more examples) and a webcam.   

2. Photographs of Lab Setups
Take photographs of lab setups so you’ll remember next year how you set it up. Embed the photos into lab handouts and add annotations and directions.

3. Science Photo Gallery

"Where Sand Meets Sea" by Kelsey Rose Weber

Students take pictures and explain the all of the science concepts present in their photo. Display student work in the classroom and around the school. It drives home the concept that science is everywhere! Exceptional work in physics could enter the American Association of Physics Teachers’ High School Physics Photo Contest

4. Photo/Video Analysis
This is different from #3 in that students would need to take a photo (student-created or teacher-created) and mathematically analyze it.  For example, students could photograph the water coming up out of the water fountain.  From the size and shape of the parabola, students could determine the initial speed of the water and the time it spends in the air. See also Speeding Problem and Kobe, Karplus, and Inquiry.

5. LED Motion Photos

by Amy Snyder, 2007

Students would take pictures with the shutter open a little longer than normal to capture motion.  Attaching LEDs to the subject would allow for “light traces” in the photograph.  See Sebastian Martin’s A Different Physics Class.

6. A super-accurate stopwatch
Many cameras have a video mode.  It could be used to film an event that takes such a short time (less than 2 seconds) that using a regular stopwatch would yield poor results because of human reaction time.  For example, students could measure the time it takes a ball to fall from the ceiling to the floor (which is less than 1 second) to determine the gravitational acceleration.  Recently, we were doing a lab where students studied how the spacing between dominoes affects how quickly the line of dominoes fall. Students were getting messy data because the falling times were so short.  If students had taken a video of the dominoes, they might have gotten more accurate falling times because they can look at it frame-by-frame at 30 fps.

7. End-of-year slide show for final exam review.

Make a  slide show from pictures of students doing lab work and participating in demonstrations.  At the end of the year,  use the slide show to review for the final.  Ask the students if they remembered what happened in the lab/demo and what concept it demonstrated.  Plus, it’s a great way to remember all the good times  during the year!

8. Video-based Labs
Sometimes, I only have one lab setup because the equipment is expensive or finicky. I used to run these as teacher-led demonstrations.  Now, I can take a video of the experiment in action and students get the data from the video and do a regular lab analysis.  Students must still recognize what data is important and know what to do with it, as with a traditional experiment.  For a great example, see: Coin on Rotating LP. (Be sure to click “Home” to see many more!)

9. Archiving Student Whiteboard Solutions

In groups of 3, my students often write-up problem solutions on large whiteboards and present them to the class.  Taking pictures of the whiteboards and archiving them on the class website would be perfect for student review and for students who were absent that day.  If that gets too much to handle (sheer volume), take a picture of an exceptionally well laid out solution and put it in the “Whiteboard Hall of Fame” or the “Whiteboard of the Week.”  Documenting exemplary work shows students the level of expectation we have for all of them! See more at Physics Whiteboards.

10. Mini Biography
Take pictures of students and attach to a mini biography students would submit at the beginning of the year.  Display bios around the room so you not only get to know your students, but they can learn more about each other! See an example from Dean Baird.

11. Picture Dictionary

"f=force" copyright AshleyJM

As a class create a picture dictionary where students take photos that illustrate a particular science concept (force, velocity, wave, force, charge, momentum, energy, equilibrium, etc). These pictures could be posted around the room, perhaps with equations added, as the year progresses. Much better to have student made posters than teacher ones! See the brilliant and clever Flickr photoset The ABCs of Physics.

12. Photo labels for equipment drawers
With all the equipment in science rooms, photo labels would be a great way to show the contents of the drawers to help students find things and to put them away. Plus, the photos would liven up the room!

13. Video lab reports

14. Safety Do’s and Don’ts
At the beginning of the year, all science teachers go over laboratory safety and have students and parents sign a safety contract. Creating a PowerPoint with photos of do’s and don’ts would be perfect! Plus, it could be pretty humorous. If the pictures were created by the class from the year before as a final project, the next year’s students would enjoy seeing their friends in the photos.

15. Demonstrations

In the above video, which cart felt more force? (i.e., which cart’s hoop flexed the most?) When debriefing after a demonstration, there are always a bunch of students who think they did/saw something that they really didn’t. They might be biased going in to the demo, and the demo doesn’t change that bias. By taking video of the demo, show them what REALLY happened. In the above video, students tend to focus on the speed of the carts, rather than the flexing of the hoops, even when you tell them to look at the hoops!

(NOTE: Some media in this post may not display in feed readers and must be viewed on the website.)

Falling Rolls

Rotational motion is my favorite topic in AP Physics C: Mechanics. Here’s one reason why:
[taken from Why toast lands jelly-side down: zen and the art of physics demonstrations by Robert Ehrlich]

We did this as a final problem in our study of rotational energy. After working through a series of long equations from energy and kinematics, we discovered the final answer is surprisingly elegant:

UPDATE 12/27/2010: Thanks to Dan Fullerton’s class for catching our error. They analyzed the problem using a torque approach and came up with:

I double-checked our energy approach and now get the same answer as Dan. We must have made an algebra mistake somewhere. This is why I love physics — there is more than one way to solve a problem!

H is the drop height of the free-falling roll, h is the drop height of the unrolling roll, r and R are the inner and outer radii of the unrolling roll.

Using large rolls of paper towels, we tested our prediction. Here’s the result, captured in slow motion:

(Despite our mistake, the demo still works. From the video, it seems the students did not release the rolls simultaneously. Perhaps this compensated for our algebra error.)

They were just a tad excited when it worked. And yes, that class is all boys, much to my dismay.

What’s your favorite activity or demo for rotational motion?

Visualizing Newton’s 3rd Law with Colliding Carts

Compare the amount of flexing of the 2 metal hoops when the carts collide. What does this tell you about the size of the forces acting on the carts during the collision?

(For frame-by-frame viewing, click the “.mp4″ link. When the video plays in your browser using Quicktime, pause the video before the collision and use the left-right arrow keys to advance the video one frame at a time. Compare the sizes of the hoops!)

FAST vs. SLOW (same mass)

Download now or watch on posterous

FastSlow.MP4 (1932 KB)

HEAVY vs. LIGHT (same speed)

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HeavyLight.MP4 (3646 KB)

HEAVY (moving) vs. LIGHT (at rest)

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HeavyIntoLight.MP4 (7620 KB)

HEAVY (at rest) vs. LIGHT (moving)

Download now or watch on posterous

LightIntoHeavy.MP4 (4048 KB)