Physics & Physical Science Demos, Labs, & Projects for High School Teachers

Archive for January 2009

I’ve always been a lover of science and I’ve had my early bouts with pseudoscience.  I think if you talk to most science lovers, we all investigated several topics in pseudoscience.  Let’s face it, I would love for UFO’s to be space aliens.  And who wouldn’t want to have a superpower?  But they aren’t and we don’t.

As a teacher, I was originally amused by it.  Now I battle it head on.  Many people take a “what’s the harm” view of these topics.  I think that is dangerous.  We need to teach our students to use critical thinking skills.  My wife doesn’t get this.  She thinks the Eagles will lose if she is in the room where the TV has the game on.  I usually respond by telling her that the Eagles management called before the game started and they asked her to please not watch.  Sounds crazy, doesn’t it?  If we believe in one form of hocus-pocus, we fall prey to the next one.

Check out the website whatstheharm.net.  You will get a sense of what happens when we sit by and allow mysticism to rule instead of science.  The page comes off a bit militant, but the underlying facts should at least make you think.  Perhaps one of the more dangerous trends are the anti-vaccination groups.  They want us to think there is a mass conspiracy and vaccines are bad.  What they are doing is actually causing outbreaks of diseases by reducing the “herd immunity.”  The herd immunity, if I understand it correctly, essentially doesn’t give a disease enough places to gestate and grow.  When the population reaches a certain vaccination level, say 95%, then the entire population is basically protected from epidemics.  If the population gets under that threshold, we are opening ourselves up to serious problems.  Don’t trust me, do your own research.  In other words …

Be a skeptic.  I don’t like the word because most people don’t understand what it means.  They think a skeptic is a nay-sayer.  A skeptic simply insists on proof.  The more outrageous the claim, the more proof is required.  A skeptic changes their position if the facts lead them down a different path.  My skeptical radar goes off any time someone says, “they say….”  It’s as simple as someone telling me, “they say it’s going to snow 12 inches tonight.”  Rather than take the store clerk’s weather knowledge on faith, my response is to check the weather forecast when I got home.  Not an outrageous claim for January, so it doesn’t require much proof.  I just want the facts directly from the experts, not second, third, or fourth hand.

There are a number of outstanding skeptical podcasts that are highly entertaining, educational, and just plain fun to listen to.  You can find them on iTunes for free.  If you aren’t listening to podcasts, you are missing a world of excellent quality entertainment.

I highly recommend:

  • Skepticality
  • A Skeptics Guide to the Universe
  • Are We Alone?  SETI Science and Skepticism
  • Science Talk: The Podcast of Scientific American

These are a few of my favorites.  There are more, but these will get you started.  After listening to a few of these shows I realized I’ve been a skeptic my entire life.  I didn’t know there was a name for it, and more importantly, I didn’t know there was a whole community of people out there just like me.

You are not alone.

(This was submitted by Duane, a High School teacher in Georgia.  Thank you Duane.)

One fun “observation vs. conclusion / assumption” demo that I love came from Flinn Scientific’s “A Demo A Day” for Chemistry. I call it the “Potato Candle”.

Cut a cylindrical core (apple corers work well) from a potato – rinse it in lemon juice to preserve the near-white color of the cut potato – then cut a cross in one end. Insert an almond sliver (available at any grocer in the baking goods aisle) into the sliver. Your “candle” is now ready for the discussion / demo.

Inform your students that they are to practice their powers of observation, and make as many observations about what they are about to see in a limited time frame. Turning the lights down or out aids in their “mis-observations.”

Light the almond sliver with a match – it will catch readily, and burn for about 2 minutes – so don’t give them much longer than 60 seconds to make their observations. Blow out the almond before it burns out, turn on the lights, and start taking notes on the board as to the observations the students made of the “candle.”

At some point, particularly effective after someone makes the observation that the “candle” is made of wax, note that that’s an interesting observation, calmly bite the potato candle in half, chew and swallow. Your students will be aghast for a moment, wonder if you’re as crazy as that seems, and it leads into a lively discussion on the differences between observations, conclusions, and assumptions based on previous experiences.

Hope you like it!

Duane

There is no easy way to demonstrate this in writing, so I will be brief. (Maybe I’ll video this at the gym tomorrow night and post it here.)

A key to martial arts is using an attackers momentum against himself. We don’t want to use direct force against an attack when a small redirecting force creates so much more havoc.

The move I have in mind is when an attacker is swinging a sucker punch or roundhouse punch. By blocking and pulling on both the punching arm and neck of the attacker, you can send them down to the floor. ( I don’t recommend this to those without some serious martial arts training.)

The physics here is all about impulse.  My effort is minimal, I use a very small force to add to their momentum and throw the attacker off balance.

Yeah, like I said, I need to make a video of this one.

I realized tonight, as I start to plan my lessons for the week,  that I don’t have much here on momentum. This is a pretty straight-forward section. It’s easy to teach and should not be confusing to students that do the barest amount of studying.

As a quick summary, I teach momentum and impulse, skip angular momentum, then teach conservation of momentum.  Not all the books discuss elastic and inelastic collisions, but I think that is rather critical to the subject.  I also stop short of including the energy section.

Once I start conservation of momentum, I talk about what happens when people don’t wear seatbelts.  I teach high school seniors in Philadelphia, many of them are just getting their license because they use public transportation to get around.  I drum into their head the need for seatbelts.  One way to do this is to figure that a car traveling at 25 m/s (about 55mph) hitting a tree would compress perhaps 1.5 meters while coming to a stop.  I calculate the time to stop is about .12 seconds.  Using the impulse-momentum theorem, I get a figure of about 300,000 Newtons of force.  I’m sure car manufacturers have better numbers, these are just an estimate.

For demos, I have something call “slippery alley” that was purchased through Frey.  There is a sled that wants to separate because of a rubber band, but it is held together with a string.  The alley is a metal trough filled with plastic microspheres creating a nearly frictionless surface.  Since one part of the sled is twice the mass of the other, when they seperate (in opposite directions), the lighter mass is traveling twice as fast as the heavy one.

The worksheet I’ve attached was very carefully researched.  All the masses are accurate, as are the velocities of the projectiles.  If you find any errors, please let me know.

momentum-problems.doc


What’s New in 2013/2014?

Every year brings a change, this one is no exception.

I will be picking up the sophomore honors Algebra II class to keep them separate from the juniors. This should help accelerate them and put them on a stronger track towards Calculus. Looks like there will be only one section each of Physics and Calculus, but still two of Robotics & Engineering.

Hot topics this year are going to be the Common-Core Standards, Standards-Based Grading (SBG), improving AP Calculus scores, and somehow adding Python, maybe as a club.

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Just a quick poll to help me understand who is stopping by my blog.

Yeah sure, lots from America, but look who else is here…

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