Homemade Hovercraft

Inspiration
This is more of a build/craft project instigated by my friend Brian's suggestion.  We'll be trying to construct a hovercraft from a sheet of plywood, a shower curtain and a leaf blower.

Materials
4x4 sheet of plywood (we used 15/32" thick)
1 shower curtain you don't mind cutting up (the heavier duty the better)
duct tape
a few dozen thin strips of corrugated cardboard about 1/2" x 3"
sharpie and string.
staple gun
drill
A few screws (just long enough not to poke through 2 layers of the plywood)
portable jigsaw
sand paper with blocks

Discussion Notes
We talked about air pressure building up to inflate the membrane in to a toroid or bagel shape making a nice smooth contact with the floor and when air comes out of the holes in the middle of the toroid with a good smooth surface and a centered rider it has no easier path in any particular direction and eventually pushes its way out in all directions equally under that smooth surface.  That flowing air in all directions creates a cushion that give us our hover effect.  We also talked about what happened when the rider leans one way or isn't centered.  We also discussed what would happen if the surface of the floor were different (rough floors could lead to tears in the membrane, carpet would lead to no liftoff at all since the air could escape through the carpet fibers more easily than lifting the craft at all.   

Build Notes
 I want to have the girls do as much of the actual construction as possible, that means all of the measuring and non power tool based cutting etc.in this entry I'll give detailed measurements I happened to use (I'd seen a couple finished product videos but mostly eyeballed all of the sizes but measured arcs and centers very carefully).


Step 1 Main Disk
We took the 4x4 sheet and traced a circle a couple inches away from the edge (43" diameter is what we ended up with but using a string and sharpie as a compass piloted by an 8 year old it's mostly important to shoot for a smooth circle over any specific size in the same diameter ballpark). Once that was traced we propped the sheet on a couple of sturdy boxes (recycle bin and a pink chest cooler in our case) and have the kids brace it while I cut out the disk with the portable jigsaw. Once that was done I had the girls sand the edges as well as they could with 100 grit paper and blocks, this is important to prevent tearing on the edge of the plastic.

Step 2 Blower Hole
Trace the edge of the leaf blower nozzle about halfway between one of the edges and the center of the disk. Drill a pilot hole inside the tracing and then cut that out.  After sanding line that hole with duct tape to make a better seal with the nozzle, which also needs to be wrapped in duct tape till it's able to make tight fit..

Step 3 Disc Clamp
Trace a circle on the largest of your leftover corners of your 4x4 sheet between 6 and 8 inches.  We used a paint can for this as it's easier than compass work and is a workable size at about 7 inches.  Cut that disk out and sand.

Step 4 Plastic Membrane
Lay the plastic out flat and wrinkle free and then lay the sanded and cut disk on the center of the sheet (standard ~70x70 shower curtain works).  Once that is roughly centered cut a circle with scissors about 4 inches wider than the main disk.  Next pull that over the disk and staple it down with the thin strips of cardboard as a pad between the sharp staples and the fragile plastic to prevent rips (be generous with the staples and hammer them in flat and tight).

Step 5 Disk Clamp Attachment
The small disk will go in the center of the plastic membrane on the bottom but before we screw that on we reinforced the plastic there with a layer of duct tape going out about 3 inches past the disk clamp.  Once the duct tape is down and center is found we held the disk clamp in with a few wood screws (careful on the length so they don't poke up through in to where the kids will be sitting on the other side).  Clamping the small disk in the middle of the membrane will give the desired toroidal shape.  Once that is secured cut about 10 one inch v shaped slits in the duct tape reinforced plastic membrane surrounding the disc clamp (this is why the reinforcement is needed otherwise these holes would quickly tear the whole plastic skin).

Step 6 Final Assembly
Attach the leaf blower nozzle to the tape lined hole while sitting in the center and enjoy!

Primary materials

My build team proud of their big circle.

Staple and hammer teamwork action.

Trimming the excess plastic after the stapling is done.

First flight.

Noelle get's her turn (notice how she sits in the very center)

Top view of the finished craft works great indoors too.

Bottom view shows disc clamp and reinforcing tape (as well as a patch  we had to put in under the nozzle port after a fairly hard landing)

Hot vs Cold round 2

Inspiration
This event started with thinking about the previous event I did with the girls on the limitations of our sensation of heat and temperature differences with 3 bowls of water, hot, warm and cold.  In that version you can get disparate sensations from the warm bowl from hands that had previously been in the other two bowls one feeling cold/colder and the other feeling it as hot/hotter.  I wanted to explore one of the other common misinterpretations from our sense of touch about temperature, in particular insulators and conductors of heat.

Materials
Insulated cutting board (same temp as the counter)
Granite  counter top (same temp as the board)
IR thermometer
2 Ice Cubes

Notes
First part was to have the girls feel both surfaces and make observations on how each feels and make estimates on relative temperatures.  Once they've done that we used the IR thermometer to confirm that they were nearly identical temperature and discuss further. They both had observed that the counter felt cooler than the cutting board and when they discovered the truth didn't quite understand why their fingers were deceiving them.

The second part was to go in another direction to illustrate other ramifications of the disparate heat transfer rates of the materials.  To do this I got two fresh ice cubes from the freezer and asked them (with them knowing that they were the same temperature and that the counter felt cooler).  They both took the bait and guessed that the warmer feeling (and slightly warmer actual temperature) cutting board would melt the ice faster.  It was obvious right away how the counter was melting the counter far faster and after 3 minutes the counter cube was all gone and the other was barely changed.  At this point we talked about material differences of insulators they knew about like Styrofoam coolers and travel coffee mugs versus things like stone and metal pans.

After thoughts include having them explain what we did to their mother and revisiting what we learned about limitations of our sense of touch and noting temperature differences.  Bringing up how much of a difference there is between thermal conductivity of air vs water and how that affects how cold air vs cold rain feel (and the ice demonstration was a way to reinforce that it's not just a sensory trick or limitation of our skin like with the water bowls).

The fancy materials for this demonstration.

Initial observations

Phase two begins and Lana notices rapid melting on the counter.

After 1 minute the granite cube is diminishing rapidly.

The insulated board cube is hardly changed and the granite cube is completely gone.

Bernoulli's Hair-dryer

Inspiration
Floating balls over a wind sources are a staple of hands on science museums and kids science books.

Materials
Ping pong ball
Electric hair-dryer with cool air setting (don't want to melt the ball)
Toilet paper tube or paper towel tube

Notes
The setup couldn't be easier for this one as all you do is point he hair-dryer up and set it on high speed with cool air and have the kids drop the ball in to the flow and enjoy.  It helps to illustrate the power of the Bernoulli principal effect here if you not only show how it can make the ball hover with the dryer pointed up but also at an angle so that the ball is clearly hovering to the side of the blower so it's obvious that it's not just wind "pushing up".  After they've had a change to play with how the laminar air flow traps the ball in various ways add the tube from above the ball and watch the ball shoot out of the top at a decent clip.

Stamspud Launcher Lite

June 20, 2012 

Inspiration

I read about this variant potato launcher in the book Totally Irresponsible Science from which I'll be mining many other fun demonstrations and 'experiments".  Also http://www.education.com/activity/article/potato-cannon/ has good info for this design cannon as well.

Materials
4' length of 1" schedule 40 PVC pipe
Disposable mop (handle must fit inside PVC pipe.)
Potatoes for ammunition


Notes
This launcher involves putting potato core section on each end of the pipe and then using the mop handle to ram the bottom core up towards the top core as quickly as possible to compress the air between them and send the top spud sailing.  The results were not as spectacular as those from the combustion powered cousin that we did last year but it was certainly faster and easy to set up.  


Some setup tips for better performance we found that slightly sharpening the ends of the pipe with a knife of file allows for easier cores to be loaded and helps make for nice tight seals (sharpening the outer edge of the pipe makes for ease core cutting but doesn't improve the fit/seal like shaving the inside does).  Any dowel that fits in the tube can be used as a rammer but the disposable mop lets you anchor the bottom by standing on the mop head while you thrust the pipe downward over the handle to create the compression. When you push the dowel up in to a stationary pipe you would need to take precautions not to pinch your hand, while the mop setup avoids that hazard neatly while letting you ram with as much force as you like.


Our results varied a good deal ranging from 25' high launches up to near 70' or 80' I'd guess.  Depending on potato size and pipe diameter you can get many shots per potato, simply reloading the empty end after firing and firing again.  Unfortunately we didn't get any pictures of this event while we did it up at my parent's house in Jackson NH

Friction More of Less

It's been a year since I've blogged though we've still been doing Science Saturday events (I've just been too much of a slacker to write about it).  As Noelle's about to finish elementary school for good I'm inspired to do a little back-filling from this last year.  I'll start with her science fair project from this year about friction (in this case I'm just going to post the details in her own words).

Friction More of Less

Question:

What type of material (normal, sand paper, felt, cloth, or rubber) should a kid use if the faster you go on a slide the more fun it is?

Hypothesis:

I predicted that cloth would have the least amount of friction because cloth slides like socks on hardwood floors.

Procedure:

I used a slide, a protractor, a hinge, two long wooden blocks of the same size, four small square wooden blocks, a piece of sand paper, cloth, felt, and rubber. I determined at what angle each material slides at. The higher angles correspond to more friction and lower angles to lower friction.

Results:

The felt block had the lowest amount of fiction because it slid at the lowest angle and the sand paper block slid at the highest angle so it had the most friction.

Follow Up Question #1:

I was surprised that the felt beat the cloth and I wondered if the reason why was that the felt had less surface area touching the slide than the cloth. So I tested two felt blocks with different surface areas to see if it mattered to friction.

Follow Up Results #1:

• Felt #1 (big surface area): 16, 21 degrees
• Felt #2 (small surface area): 22, 26 degrees

I was surprised to find that the bigger the surface area, the smaller the friction.

Follow up Question #2: I also wanted to see the effect on friction when the blocks had more weight. So I doubled the weight by stacking 2 blocks on top of each other and doing the test.

Follow Up Results #2:

No covering: 38, 40 degrees

No covering double weight: 40, 43 degrees

Felt #1: 16, 21 degrees

Felt #1 double weight: 19, 20 degrees

It really surprised me that there was not a huge difference between the normal weight and the doubled weight though they are the same material so they may create the same amount of friction.

Conclusion:

I originally wanted to figure out how to have the most fun on a big slide by finding a way to slide down faster. These experiments told me that of the materials I tested, a felt bag would give me the best ride. I also found that in the bag, you will go faster if you spread your weight out. Finally based on my experiments, I am happy to report that kids should go faster on a slide than

By Noelle Stam

5^th grade Mrs. Cashin

April 18, 2012