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Let The Sun Shine In!
For this experiment you will need a window that faces either East or West, and you must be able to place a glass on the sill of the window so that the sun shines across the rim of the glass onto the floor of the room.
Things you will need:
1 - tall water glass.
1 - window with sunshine.
Enough water to "overfill" the glass.
How to make a rainbow:
Ideally, this tutorial is about surface tension. Think of gravity on a molecular level. All mass has gravity. The denser the mass, the greater it's gravity. Also, the larger the mass, the more gravity it has.
Take your glass and place it on the window sill so that the sun shines across the rim of the glass, and onto the floor. You will have to time this with the rising or setting sun, depending on your situation.
Fill the glass with water all the way to the rim, then keep filling until the water actually is higher than the rim of the glass. Don't let the water spill over, but you need it to sort of dome over the rim. The sun will shine through the water that is higher than the rim of the glass and create a rainbow on the floor of the room.
How does it work:
Something called surface tension keeps the water from spilling over the rim of the glass, even though the water level is higher than the rim of the glass.
When your glass is level full, you may want to use an eye dropper from that point to fill it as much as possible without the water spilling over. The water that is rising over the rim of the glass acts as a prism and separates the rays of sunlight. The curvature of the rim of the glass actually adds the curve and eventually, the rainbow effect ont the floor.