We think of taking tests as something to assess whether we learned something, but there is a fascinating set of literature that shows that it does more than that. Tests can be learning events in their own right. It makes sense when you think about it. How is it that we learn things? By making neuronal connections, or strenthening neuronal connections, in the brain. Each time we take a test and are asked to recall information, that neuronal path gets strengthened. That’s why flash cards are useful. One of the seminal papers on this topic is The critical importance of retrieval for learning by Karpicke and Roediger.

• When someone recalls something from memory, they’re more likely to be able to recall it again later — much more so than when that information is just presented to the person.
• People forget information more slowly when tested on it
• Asking people questions whose answers involve numbers increase people’s retention of numbers presented in text (by directing their attention to the type of information important to learn for the test)
• Questions asked before a task can activate prior knowledge and focus students on the relevant material

Robert Bjork of UCLA, who studies learning and forgetting, has written extensively on this topic, especially given that students don’t really know how it is that they learn, and their study habits don’t make the most effective use of what we know about our cognitive function. His “how to succeed in college” paper is a nice summary of this research.

But, you might ask, what if you take a test and get the wrong answer? Doesn’t that then cement the wrong answer in your brain? So isn’t there a danger to testing ourselves when we might get the wrong answer stuck in our head? Some research suggests that testing could distort knowledge in this way: When you get the wrong answer on a multiple choice test, you’re more likely to make that same mistake on a later test.

Giving someone feedback on their performance on a test can reduce memory distortions, but this is sometimes not feasible (especially in today’s climate of standardized testing). Luckily, new research shows that, no, making mistakes still helps us learn. A set of two articles authored and co-authored by Nate Kornell sheds some light on these questions:

• When they tested students before they studied a text, students did better on a test after having studied the text, even though they got most of the questions wrong. This appeared to be due to the testing itself, rather than focusing students’ attention on the important aspects of the text, because students learned better when tested than when key information in the text was bolded. (Note the implications for students’ exuberant highlighting of texts!)
• This kind of testing also reduced forgetting after a one week delay.
• This kind of testing was also more effective than reading the same question and trying to memorize the words of the question itself (without trying to retrieve the answer).
• In another study, where students were doomed to fail (being tested on word association pairs that most people get wrong), they found the following: Trying (and failing) to answer a question, and then studying it, produces better learning than studying it (for a longer time) without first trying to answer it.

Thus, give your students pre-tests! The act of trying (unsuccessfully) to retrieve an answer helps you do better on a later test (and not just because the pre-test gave you a clue as to what would be on the final test). Pre-processing is very important!

It’s crucial, however, that students be given a chance to restudy the tested material.

Scientific American article

Nate Kornell’s website with links to his publications. (Gosh, he’s cute!)

Originally posted on my sciencegeekgirl blog.

Photo by Patrick Hannigan (click photo for Wikimedia link)

I recently read two interesting articles on translating science for the public — in particular, why we give lectures for the public at all, and some effective ways to do it.

For those of you who are interested, here are the original source articles:

1. Explaining the Unexplainable: Translated Scientific Explanations (TSE) in public physics lectures, Kapon, Ganiel and Eylon, International Journal of Science Education, 785022307, p 1-20 (2009)
2. Scientific argumentation in public physics lectures: bringing contemporary physics into high- school teaching, Kapon, Ganiel and Eylon, Physics Education, 33 (2009)

Carl Sagan — the quintissential expert lecturer

Contemporary physics topics are inaccessible to most high school students. They need a lot of prior knowledge to follow them, which they don’t have yet. So, we are often presenting complicated ideas to an audience who knows nothing about this. But there’s another forum where we do this quite regularly — public science lectures. What do effective public lectures have to tell us about explaining complicated concepts to high schoolers?

How do we translate complicated ideas to a lay audience, without being inaccurate? We must walk the fine line between understandability and inaccuracy. My old mentor, Paul Doherty at the Exploratorium, taught me to think carefully about this line. You can’t be as accurate and detailed as you might want to be when explaining things to the public. As scientists, we are used to giving every caveat and detail in order to have no way to be misunderstood. As communicators, instead, we need to leave out those details, and do our best at being understood in the broadest sense.

In public lectures, we are just promoting a sense of understanding and engagement, a “wow” factor, rather than deep understanding. But this is a laudable goal. Science is a cultural endeavor, just like music, and good lectures give people a window on this culture. One can liken it to a music performance. Someone who has not studied music will experience a concert on a very different level from someone with a PhD. But they can still appreciate the beauty and aesthetic, and enjoy dipping their toes into this different world. Similarly, physics lectures can give people a sense of what people do with physics in the real world, which is as important to science literacy as an understanding of scientific content.

There’s not much research on how “expert” lecturers manage to convey complex topics in this way. So, these authors wanted to define just what it was that makes a good public lecture. They gave three public lectures, and surveyed high school students and teachers afterwards to assess the impact. This is a preliminary study, with just three lectures.

Not unsurprisingly, there was a big gap between the content in the lecture and what audience remembered and understood. However, if the audience felt that they completely missed understanding the content, then it’s very demotivating. So the lecturers had to find some way to bridge the gap in audience understanding, to give them some sort of explanatory framework. They found many charismatic lecturers, but many of them lacked the strength of explanatory power that is created by inclusion of the following elements.

Four aspects of successful lectures (as defined by these authors):

1. Use analogies, metaphors and visuals.

Explain something new in terms of something known. For example, “A quantum particule lives through many parallel histories, as long as it does not leave a mark.” They found that many audience members used these same analogies when summarizing the lecture. These devices are used more in public lectures than in classroom lectures to bridge the gap in understanding.

2. Tell a story

The importance of the use of humor, narrative, characters and protagonists, with cognitive conflict and some sort of surprise. Speak in colloquial, casual language.
For example, A alien comes to earth and looks at people and sees that there are older and younger people. Realizes that younger person will get older like the older person. When we look at sky we see stars. Similarly, we realize that there are older and younger stars.
These narratives provide coherence and a sense of understanding. That’s all we need in public lectures, a sense of understanding — this is not a class! After a movie, for example, we don’t ask ourselves what the meaning of the movie was during every minute — we leave the movie with an overall impression.

3. Knowledge organization

This is the structure of the lecture — using repetition, stating the outline, giving clear logic and visual aids.
For example, during one lecture an empty table of properties of elementary particles was filled in. Many lecturers repeated ideas, bringing the ideas deeper and deeper each time (”spiraling”) to drive the point home.

4. Content

This is what we usually think about when we’re putting together a lecture. What do we omit, what do we include? At what level do we go into? What do we simplify? It’s important to keep in mind people’s cognitive load — how many new ideas they can process in a period of time. This requires understanding of the audience’s prior knowledge. Lecturers most aware of this aspect of what they do.
The general rule: Omit and simplify. If you’re going to lose the audience over it, toss the complicated explanation.

How might teachers use public physics lectures in their courses?

When a subject (like 20th century physics) isn’t in their textbooks, the use of public lectures (on the web) can help them enhance their course content. The authors suggest that teachers use the previous four categories to ascertain whether a physics lecture is “good” or not, to decide whether to use in the class.

Unlike a public lecture, the goal of a physics class is for students to understand the scientific arguments, rather than just promoting a vague sense of understanding. So the lecture has to be accompanied by learner-centered activities to cement the ideas.

The authors used public science lectures as part of a course in the following way in an online course.

1. Watch lecture on own and fill out worksheet summarizing points
2. Online discussion with others about worksheet, real time viewing of desktop and comments on worksheet
3. Online discussion in class
4. Reading of popular papers and posting questions in forum, reflection
5. Created group summary of lecture, using a guided matrix. They decomposed the lecture into arguments and analyzed each argument, explaining which aspects of the scientific method were reflected in the lecture.

However, using videos or doing reflective activities like this in class take time. Many teachers in their study complained about this, and many didn’t end up using the activities for that reason. I’d be interested to hear working teachers’ take on this — would you use videos in your class and do these kinds of activities with them? What kinds of activities or videos would you use (or do you use) in your class?

In optics experiments, you often need to create lines of light. You can do this with light boxes, but they’re expensive, and tend to have too many rays to be useful. Laser light boxes are great, but again, spendy.

One teacher recommends using laser levels. These are the things made to help you hang pictures on a wall, so they’re level. Less than $20! It’s made of a bright laser, with a cylindrical lens, which spreads the dot into a line. You can see a demo here.

PHOTO FROM ‘HOW STUFF WORKS.COM’

Zeke writes:

They create bright, dead straight, easy to use lines of light. They do seem useful for Snell’s Law, but it isn’t always obvious how to do it. The most common way is to use a semi-circular dish. You might find that your biology teacher has absonded with them, too. Filled with plain Jello, the rays are really clear. You can’t see the protractor I photocopied and placed under the tray, but it works great. You can also fill them with other substances like water and corn syrup to demonstate different indexes of refraction. However, ray needs something to scatter it so you need to stir in some milk or other colloid. Another option is to get a fine grit sand paper and roughen the bottom of the dish. This will scatter the light through diffuse reflection.

I also like to use plastic bars. You might already have glass plates, but they are surely too thin. The ray of light made by the laser level is thick and if the object is too thin, the ray will go over the top making for a confused appearence.

I made the plastic bar by buying a thick hunk of clear plastic from the discard bin at TAP Plastic. I had them cut it into pieces. I bought six grits of sand paper and progressively sanded the bars until they were clear. The final bit required a liquid polish. The people at TAP explained how to do it to me.

It’s pretty cool and can show total internal reflection really great.

Here’s a video from Teacher Tube

Have fun,

Many thanks to Marc “Zeke” Kossover for this information.

Originally posted on my sciencegeekgirl blog.

If you’re a teacher — of physics, or any other physical science — and haven’t yet picked up a copy of Edward Redish’s Teaching Physics with the Physics Suite , I’m making a bid right now that you do so.

I finally read it — really read it — instead of just browsing through a chapter that I needed to reference for a paper. For a slim volume, it is a surprisingly powerful compilation of effective teaching techniques based on research, and what you as an instructor need to do in order to implement them to their maximum power.

First he goes through a wonderfully succinct summary of what cognitive research can tell us about teaching — the book is worth buying just for these 30 clear pages.

He goes on to discuss exams and homework — the goals of assessment and different types of questions. He has a resource CD with a bunch of research based surveys, like the Force Concept Inventory, or different attitude surveys. He then gives a quick look at some of the major research-based teaching methods, like Peer Instruction (PI), Interactive Lecture Demonstrations (ILDs), Tutorials, and Just In Time Teaching (JiTT). It’s certainly more useful for teachers of physics (at any level) but I think that most people teaching the physical sciences will come away with something useful from the book.

Here’s a gem.

I had been teaching for 20 years before I realized that when students asked me questions, I was responding as a student rather than as a teacher. Having been a student for 20 years, having been rewarded for giving good answers to teachers’ questions, and having been successful at getting those rewards, I had a very strong tendency to try to give the best answer I could to any question posed. Once I realized (embarassingly late in my teaching career) that the point was not getting the question answered correctly but getting the student to learn and understand, I shifted my strategy.

Now, insted of answering students’ questions directly, I try to diagnose their real problem. What do they know that they can build an understanding on? What are they confused or wrong about that is going to cause them trouble? As a result, instead of answering a question right off, I ask some questions back. Often, I discover that students are trying to hide a confusion by creating questions that sound as if they know what they are talking about. Helping them to find resources within themselves that they can bring to bear often makes all the difference.

Redish, “Teaching Physics with the Physics Suite,” (2003), p. 190.

I feel like I keep posting these, I should compile them.

Currki : Currki, an open source website for educational materials k-12 has over 80,000 members who are educators and teachers.

TeacherTube TeacherTube is a video sharing website based on YouTube. It is designed to allow those in the educational industry, particularly teachers, to share educational resources. To dates TeacherTube has 380,000+ members.

Next Vista Learning Next Vista is an online library of free videos for learners everywhere. NextVista.org believes learning is stronger with teachers and students from all over the world contributing content. They have a membership of 6,000 contributors.

Watch Know: A collection of some of the best free educational videos made for children, findable and watchable on one website. Lots of wonderful videos on science, compiled from multiple sources.

Meet me at the Corner ( www.meetmeatthecorner.org) is a series of videos for children in the form of a video podcast. Each video is linked to fun websites and a Learning Corner of questions and extended activities. New episodes are uploaded every two weeks. The author says:

Take a look at the new virtual field trip to Divide, Colorado to the Colorado Wolf and Wildlife Center. Our young host Amanda learns about reestablishing the wolf population in the southwest and hears the howl of a wolf pack

Photo: Flickr by djcramer at http://www.flickr.com/photos/cramer/810819/.

Originally posted on my sciencegeekgirl blog.

Below I am reposting a rather long piece taken verbatim from the website of Steve Detweiler who just says that it’s an “amusing anecdote from a friend of mine.” So, I’m not sure of the veracity of the story, and some claim that it’s an urban legend. It may well be. But it opened up some deep discussion on the PHYSLRNR email list, which I attempt to summarize below.

HEAVY BOOTS

About 6-7 years ago, I was in a philosophy class at the University of Wisconsin, Madison (good science/engineering school) and the teaching assistant was explaining Descartes.

He was trying to show how things don’t always happen the way we think they will and explained that, while a pen always falls when you drop it on Earth, it would just float away if you let go of it on the Moon. My jaw dropped a little. I blurted “What?!” Looking around the room, I saw that only my friend Mark and one other student looked confused by the TA’s statement. The other 17 people just looked at me like “What’s your problem?” “But a pen would fall if you dropped it on the Moon, just more slowly.” I protested.

“No it wouldn’t.” the TA explained calmly, “because you’re too far away from the Earth’s gravity.” Think. Think. Aha! “You saw the APOLLO astronauts walking around on the Moon, didn’t you?”

I countered, “why didn’t they float away?”

“Because they were wearing heavy boots.” he responded, as if this made perfect sense (remember, this is a Philosophy TA who’s had plenty of logic classes). By then I realized that we were each living in totally different worlds, and did not speak each others language, so I gave up.

As we left the room, my friend Mark was raging. “My God! How can all those people be so stupid?” I tried to be understanding. “Mark, they knew this stuff at one time, but it’s not part of their basic view of the world, so they’ve forgotten it. Most people could probably make the same mistake.”

To prove my point, we went back to our dorm room and began randomly selecting names from the campus phone book. We called about 30 people and asked each this question:

1. If you’re standing on the Moon holding a pen, and you let go, will it
a) float away,
b) float where it is,
or c) fall to the ground?

About 47 percent got this question correct. Of the ones who got it wrong, we asked the obvious follow-up question:

2. You’ve seen films of the APOLLO astronauts walking around on the Moon, why didn’t they fall off?

About 20 percent of the people changed their answer to the first question when they heard this one! But the most amazing part was that about half of them confidently answered, “Because they were wearing heavy boots.”

MORE ON THE BURNING QUESTION OF HEAVY BOOTS

I decided to settle this question once and for all. Therefore, I put two multiple choice questions on my Physics 111 test, after the study of elementary mechanics and gravity.

13. If you are standing on the Moon, and holding a rock, and you let it go, it will:
(a) float away
(b) float where it is
(c) move sideways
(d) fall to the ground
(e) none of the above

25. When the Apollo astronauts were on the Moon, they did not fall off because:
(a) the Earth’s gravity extends to the Moon
(b) the Moon has gravity
(c) they wore heavy boots
(d) they had safety ropes
(e) they had spiked shoes

The response showed some interesting patterns! The first question was generally of average difficulty, compared with the rest of the test: 57% got it right. The second question was easier: 73% got it right. So, we need more research to explain the people who got #25 right but did not get #13 right!

The second interesting point is that these questions proved to be excellent discriminators: that is, success on these two questions proved to be an extremely good predictor of overall success on the test. On the first question, 92% of those in the upper quarter of the test score got it right; only 20% of those in the bottom quarter did. They generally chose answers (a) or (b). On the second question, 97% in the upper quarter got it right and 33% in the lower quarter did. The big popular choice of this group was (c)…33% chose heavy boots, followed closely by safety ropes at 27%.

A telling comment on the issue of fairness in teaching elementary physics: Two students asked if I was going to continue asking them about things they had never studied in the class.

———————————

First off, here’s the physics. Earth is not the only thing with gravity. The moon exerts a gravitational force on things, but it just exerts less force, mostly because it’s just got less stuff. Stuff attracts stuff, and so less stuff will attract other stuff less strongly. If you drop a pen, it will fall slowly, because the acceleration due to gravity is weaker. Earth is far away, but that doesn’t really matter — when you are on the surface of the moon, the gravitational attraction of the moon is stronger than that of the earth. That’s why the astronauts could jump very high on the moon. You would weigh less on the moon than you do on the earth. If the astronauts jumped really really really hard, they could float away from the moon. The same is true on the earth (but to jump that hard, you need rockets, and that’s what the space shuttle does).

So, here’s the discussion. One instructor said that she had used similar questions in her class, and gotten similar results. Many students thought the pen would float away. One year, she asked them instead about a crescent wrench instead of the “apocryphal pen.” They all answered that question correctly! Another instructor, however, gave a similar set of questions to his class, and most of them answered correctly. What’s he doing differently?

What’s the problem? This question forces students to challenge a preconception that they had walking in the door — perhaps that “things float in space” or “heavy things get weighed down.” Apparently the misconception that the moon has no gravitational attraction persists through most physics courses. Even though they might be able to state that the moon has gravity (as evidenced by correct answering of the second question, as to why the astronauts stayed on the moon), they have trouble transferring that understanding to the “what happens when you drop a pen on the moon” question. They are thinking, argued one instructor, in terms of the surface features of the problem (we’re on the moon!) rather than the underlying features (all chunks of matter have gravity). Students transfer more when they’re interactively engaged in the material, says the research (e.g., Cognitive Development, 6, 449-468 (1991), Learning and Transfer: Instructional Conditions and Conceptual Change, Michelle Perry).

John Clement gave a few ideas for ways to address this misconception in class:

Given enough time you could propose a number of what-if questions which might help the TA understand what is going on. Why did the rocket have to fire its engines to prevent a crash? Why don’t rocks fly away from the moon? What force pulled Apollo 13 around the Moon? Whey when the astronaut dropped a feather and hammer did they both fall to the surface of the Moon? This last one has no heavy boots!!!

Another really important question is to ask why they think there is no gravitational attraction on the Moon. A number of students will reply “because there is no air”. The common misconception is think that “gravity” is due to the air pressing you down. Or they may say because the Moon does not rotate, as this is another common misconception. These are explained in the teachers manual for Minds on Physics, and students are asked questions
to bring out these misconceptions while building a coherent model of gravitational attraction.

So rather than attacking the “heavy boots” conception, the student has to internalize the model that there is (at least in classical mechanics) no threshold to the action of forces, and that unbalanced forces cause acceleration. Then they have to apply it to a variety of cases, of course, along the way. It helps to have them apply these conceptions to objects on other planets. So blocks of wood in a water filled bowl all float at the same level on the Moon and the Earth, but springs supporting masses are stretched less on the Moon.

So the “heavy boots” is not the primary concern. The concept of forces and acceleration are the primary concern. Once the students have a firm model of forces, and of NTNs general gravitational law, the idea that things can float on the Moon will go away.

A few more comments that I liked:

Can the boots be heavy if the astronaut is not? Are the boots heavier than the astronaut? If not, do the boots weigh down the astronaut or does the astronaut way down the boots? I think a few questions like this can make the logical inconsistency evident. (Jerry Touger)

But, countered Dave Van Domelen:

Actually, it goes along with ideas like blankets being intrinsically warm. Qualities as properties of things, rather than the result of interactions.

And from John Clement, an idea I’d never heard before:

This comes from the concept that “gravity” exhibits a threshold effect. You have to have enough of it to be pulled down, otherwise you float.

Which, pointed out a discussant, suggests that students are using buoyancy as an analogy — if you’re heavy enough you sink, if you’re light enough you float. Or, perhaps, friction is the correct model — there is a threshold at which the force becomes effective.

Of course, trying to address these misconceptions as “problems” to be plucked out of the students minds won’t work. They’re using these ideas because they fit with their experience of the world. Trying to understand their underlying conceptions (without perjoratively labeling them as misconceptions) and working from there, will be most productive. Dewey Dykstra has written quite a bit about this, and you can see my previous post on that.

Other resources:

• Minds on Physics (vol 4) has a good section on moon/earth comparisons
• An entire thesis was written on the “heavy boots” problem
• Chapter 4 (p 44-46) of another thesis also deals with this problem
• David Hammer, More Than Misconceptions” published in AJP in 1996.

Originally posted on my sciencegeekgirl blog.

A couple links that look very helpful.

100 excellent blogs for science teachers (which includes yours truly!)

Includes a bunch of teacher blogs (which seems like a great way to get some online mentorship if you’re all alone), and subject-area blogs (like physics or biology). A very useful list.

100 cheat sheets for K12 teachers

The sections on math and science include such helpful handouts as trig basics, basic principles of chemistry, how to add positive and negative numbers, from a variety of sources and websites (many from Clif Notes).

Here are a few collections of videos of science teaching and learning — useful for learning how to teach.

Annenberg:

http://www.learner.org/resources/series90.html

http://www.learner.org/resources/series126.html

TIMSS

http://nces.ed.gov/timss/video.asp

Ok, it probably wouldn’t be very yummy, but here’s another hands-on activity you can use that’s rather Halloween-like. Called “Make a ‘mummy’”, this Exploratorium activity is a great way to demonstrate how mummification works, by drying out the tissue in a fish using baking soda. Egyptians used a specific type of salt to do this, but baking soda will do the trick, giving you a tough leathery fish.

If you’d just left your fish out on a shelf, exposed to the air, bacteria and fungi would have begun to decay the fish, creating strong, unappetizing odors. Since all living things require water to survive, removing the water from the fish greatly inhibited the growth of these organisms, decreasing the unpleasant effects of rotting.

For an inquiry activity, try substituting salt for baking soda. Which one works best? (Hint: It’s not the salt).

Make him a little pyramid home. Imagine his little fishy afterlife. Bury some fishy mummy friends for him to play with.

Pyramid photo From Platonides on Flickr.

Originally posted on my sciencegeekgirl blog.

With halloween fast approaching, it’s time to take advantage of a frivolous holiday to do some fun science stuff.

No post about Halloween would be complete without a reference to the Grossology site. Scroll down for “lab activities”: This gets high marks from one teacher who says, “It has the simpliest of the slimey things, glue slime, and fake blood.”

In that vein, read the post on “how to make slime” over at Schooner of Science. The Schooner also has a recent post on zombies — an interesting story about the origin of zombies and a toxin-like powder which may, or may not, have put people into a zombie-like state.

The “whoosh bottle” is also somewhat spooky as a demonstration. And you get to talk about gas laws and combustion, too.

Fire is always fun. If you google Exploding Pumpkin Experiment or Flaming Pumpkin Experiment, you can find some great things to do with those leftover jack-o-lanterns after Halloween. Here is Steve Spangler’s version of an Exploding Pumpkin that carves itself. Most people just have the pumpkin shoot flame from its mouth. You can get lycopodium powder (from Flinn Scientific, for example), and use a syringe to spray it along candles at the bottom of a pumpkin’s mouth, creating a fireball coming out of the mouth. Obviously, t there are safety measures to consider. The video below has the best explanation of how to do this that I found.

And here are a few suggestions from veteran teacher Raleigh McElmore:

Slime: If you can score a magnetic stirring hot plate you can easily get Poly vinyl alcohol at a chemcial supply store and make up some great slime at 40 gr/L and mixing it with a bit of Sodium Borate (known as “Borax” and in many supermarkets detergent aisle) at 40 gr/L.

Your own grossology: In elementary school I always filled a big pyrex bowl with peeled grapes that had been soaked in red food coloring. This brings out the “veins” in the grapes and I announced that “eyeball soup” would be shared with the students. A chunk of dry ice, the grapes and fill the bowl with cheap fruit punch gives you a seething and bubbling drink with “eyeballs” floating around. Or you can, for realism, use sheep eyeballs. Give them to your star pupils. I’ll keep an eye out for you.

And to keep them on their toes:

A great magic trick that Penn and Teller invented is to bring two cans of sparkling soda (not anything else as this is messy). Give one can to a quiet student tell them to keep the can totally quiet. Give the other can to a hyperactive sort and tell them to “shake the can as hard as you can without touching anything”. Did I mention that this should be done outside, oh yeah, do it outside.

Take the highly shaken can, put it in plain sight and say that this is the season for strange things. Tell the students that you will change fizz in the shaken can to the quiet can. Gently touch the quiet can and touch the shaken can. Mumble incantations about AYP and other scary things. Waste at least 30 seconds in mindless babble and then take the “quiet can” and hold it high while you open it. Curve your fingers behind it and squeeze the can as you pop the lid. It will shoot fizz all over everybody as you have secretly crushed the can. After you have sprayed everyone dramatically throw the can into a nearby garbage can to avoid students seeing the crushed can.

Then quietly open the shaken can. The gas will have gone back into solution by then and it won’t do anything. Explain to the students that teachers are given these powers, but only to be used for the good. Drink the calm can and draw attention from the garbage can with the crushed evidence.

Need more ideas? Here are some links here and here and here.

Top image from Extremepumpkins.com

Originally posted on my sciencegeekgirl blog.