Our experement yesterday, took us outside to use the sun and shadows. The purpose was to calculate the diameter of the sun using a "pinhole projector".
To make the projector:
1. Use a needle, push pin, or even very sharp pencil to poke a hole through an index card.
2. Tape the index card to the end of a yard stick so that the card is perpendicular to the stick.
3. Tape a second card (without a hole) to the opposite end of the yard stick, also perpendicular.
Next you have to move the yardstick around until the top index card (containing the hole) places a shadow over the bottom index card. We were surprised how much we had to angle the yardstick to get the shadow to match the bottom card. If you look very closely at the picture above, you will see a small white circle on the card. We had to draw a line across the circle. This had to be done three different times. The boys took turns and let me tell you, that little circle moved all over the place. It was so hard to keep it still. It also didn't help when the person holding the stick would purposely move the circle, while the person on the ground chased it around. It looked a lot like a cat trying to catch a reflection. :)
We decided maybe we should switch "stick operators". This particular operator was a little more serious about keeping the circle still. :)
This is a great picture to show the top index card with the hole and then the bottom card showing the light through the hole. From there, we measured the three lines (by 16th's of an inch) and then took an average. Our average was 5/16 in. which is roughly 0.3 inches.
From there we followed the formula provided in our book. We divided the diameter of our images 0.3 inches by 36 inches (because the distance between our cards was 36 inches) which equaled 0.0083. Then we took that amount and multiplied it by 93,000,000 miles (the diameter of the sun). This gave us an answer of 775,000 miles.
Now the actual diameter of the sun is 868,000 miles so we were really pleased that we got relatively close. At the end we discussed why our calculations were different. The kids agreed that since our projector was homemade and not an actual instrument, the calculation could not be exact.
All in all it was successful. Now my little confession... My husband came home on his lunch break and checked my math. AND...I...DID...IT...RIGHT... I think I was more impressed and excited than the kids! LOL