barefoot on a bed of nails

January 8, 2014

Have you ever wondered if someone could stand barefoot on a bed of nails? Well, wonder no more!  This episode explores the pressure on your feet in that situation.  It also introduces the idea of pressure and how that relates to pounds per square inch (otherwise known as psi).

Episode 3: barefoot on a bed of nails


Quick Summary

Pressure = Force/Area

The pressure on my feet when I’m standing in shoes was found by taking my weight and dividing by the area of my shoes touching the floor.  I used this graph paper to to find the area (the 1/2″ option worked well).

Pressure = 175 pounds/66 square inches = 2.7 psi

When I’m standing barefoot on the bed of nails the total area of all the tips of the nails holding me up is around 0.35 square inches (that was an average of smaller nail tips and larger ones…the nail tips are actually all about the same size but some seem to “poke” into your skin more than others because they are slightly different heights)

Pressure = 175 pounds/0.35 square inches = 500 psi!

As you saw, that was a little too much for my bare feet!


Determine how much pressure is on your feet when you are standing on your tip-toes.  You’ll need to use graph paper to find the area.   Let’s say that you have to be able to stay on your tip toes for at least 10 seconds for it to count (none of this rocking up onto the very ends of your toes for a split second kind of stuff!).  Post your findings in the comments below.  Good Luck….I hope you can stand the pressure;)

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marshmallow cannon

November 28, 2013

Episode 2

Pressure differences can create large forces.  A great example is an air cannon.  It’s the same idea as a potato gun but instead of using something explosive to create the high pressure I’m using a bike pump.  Here’s the video:


A few details

I’ve been using this particular marshmallow cannon for about ten years now.  However I went through lot of cheaper bike pumps in the early years.  Most of the under $20 pumps just can’t handle the pressure for very long.  I finally bought a beefier pump with a gauge and it has been awesome.  I also bought one for home.  If you’re interested here is the link an amazon:
Topeak Joe Blow Sport II Floor Pump

The slow motion video I took with my camera is kinda fun.  I’m not a pro at using it yet, but I have learned that it needs to be well lit.  The lighting is not great in my classroom, but it worked OK.  The shot with the pepsi can was using 240 fps (frames per second) and the energy drink can was 480 fps.  It’s obvious at the 480 level that the video is more grainy, but it does freeze the motion better.  Here’s the link to the camera:
Casio High Speed Exilim Ex-zr200 Digital Camera Black Ex-zr200bk

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The Singing Wineglass

November 26, 2013

Hey guys,

Welcome to my first episode of Stoked About Science!

I’ll be creating frequent episodes that involves cool demos, experiments, projects and challenges.

So, without further ado I give you:


Episode I: The Phantom Wineglass;)

Here are links to the free apps for detecting frequency that I mentioned in the video:

feedback detector for apple devices

audio spectrum monitor for android devices


And here is the video with the experiment and challenge:

The experiment:

Find some open space near a school where you can make a loud distinct sound (slapping two boards together or hitting a hammer against a chunk of metal or something like that).  Stand as far away from the building as you can (at least 50 yards….100 yards is better) while still able to hear the echo of the sound you made.   Have your partner (or you) start the timer as soon as the original sound is made and then stop the timer when you hear the echo.  This is where being farther from the building makes it easier…then you have more of a delay between the original sound and teh echo.  Repeat it four more times.  Then you can use the middle time value as your average.  Next you’ll need to figure out how far you were from the building.  You can use a tape measure, or a rope or extension cord or count your steps to the wall if you don’t have any other method (then go home and measure how big your steps are).  Don’t forget to double the distance because the sound travels to the building and then back again.  The last step is to  find the speed of the sound wave you heard by dividing the distance the sound traveled by the time it took

Speed = Distance/Time.

The Challenge:

Make a wine glass sing (most thin-stemmed goblets will work—-get one at a thrift store or Walmart if you don’t have any).  If you are really good then get several and play a little tune.

Report your results:

Let me know what you got for the speed of sound by make a comment below.  I also want to see how many of you can make the wine glass sing! Email me some videos of that.

Have Fun and thanks for watching :)


Chris Stoker

PS: Students and Parents feel free to leave me a comment or shoot me an email with any feedback or suggestions on any part of this science experience.

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