It makes a great science project. Unlike most, you'll actually get some use out of it afterwards. Some of the principles it demonstrates are:

1. Optics: focusing parallel rays of incident light through the use of a parabolic mirror.

2. Energy transformation: light to heat

3. Renewable energy: solar power

Materials:

2 - 2x4 cut to 17" length (ends)

2 - 1/2" plywood cut to 1ft x 4ft (sides)

1 - 5/16" plywood cut to 18" x 4ft (backing)

1 - sheet of silvered mylar or tin foil cut to 17" x 4ft (mirror)

2 - 1/2" plywood cut to 3/4" x 12" (skewer mounts)

1 - 1/4" wooden dowel with a sharpened point (skewer)

Plus miscellaneous fasteners and spray adhesive

Tools:

Jig saw

Power drill

Drill bits

Screw driver bits

## Step 1: Optics 101: Focussing light with a parabolic mirror

The formula for a parabola is:

Y = X

^{2}/(4F)

Where:

X is the horizontal distance from the origin

F is the focal distance (a design choice)

Y is the vertical distance to the curve at any point X

See the image below for a graphical representation.

**Signing Up**

I've always had trouble with the math... Okay, maybe I haven't even tried. But when I seen the pic in the link above - making parabolic curves immediately became clear to me. The distance to the focal point to the bottom of the curve needs to be mirrored for the flat/base line below, then finding every other point along the curve is a matter of finding the right intersecting radii. It's a bit more complicated than that - but it can be figured out.

To scale it up - you can keep doubling the distances of the points on the different angles.

Then there is using wax paper. Put a point where the focus will be, then a line twice the distance of where the base of the curve (or trough) will be. Then fold the paper over to where the line meets the point, and keep folding along the line to get the full curve.

One thing you could try that *may* help is placing a transparent shell around the hot dog to help insulate it (the air inside is what actually insulates it. the shell just hold the air in place). Cut the tops off two 1 liter pop bottles, drill a hold in the bottom of each to fit over your skewer, and slide the two pieces over each end of your hot dog so they meet in the middle. Might help, but probably you just need a bigger reflector. Also, if it gets too hot that you smell plastic fumes, you may not want to eat the results ;-).

^{2}20cm = 0.2m.

0.2m * 1m = 0.2m

^{2}0.2m

^{2}* 1000W/m^{2}= 200W_{its reaLly GENUS!!!}havebeen done before , but the big one in the background is really, really interesting. Could you give us one on that one, including the metrics by which you came up with the 2KW of heat? That is daggne interesting!I am looking at designing a simply tracker for them and a base for the leg keep a look out on http://www.bonzabuy.com.au

Also might be keen on linking to this for people who want to try & build a parabolic for themselves - thanks again!