What Is a Fixed Pulley?
The three-ball instrument (model of Sun-Moon-Earth), also known as the Moon-Earth instrument, is an astronomy teaching and astronomy popularization instrument. It consists of three small balls representing the sun, the earth, and the moon. To demonstrate the three-ball relationship and some astronomical phenomena that arise from it.
Three ball instrument
- 1. The sun is made of a 100-watt light bulb with a round milky outer cover, mounted on the top of the left pillar.
- 2. The globe is made of ping-pong balls, with small iron wires obliquely penetrating the shaft, and fixed on the right shaft with a metal sheet half ring.
- 3 Pulley: At a distance of 5 cm below the hypothetical sun, fix a larger pulley on the shaft of the supporting pillar of the sun; under the straight shaft that supports the earth, install a smaller pulley that can rotate around the shaft. The ratio of the two pulley diameters is 12: 1.
- 4 Moon: Take a small ball of appropriate size with a hole in the middle, wear it on the wire, and install it on the edge of the small pulley below the globe. The height is equal to the middle of the globe. It can rotate around the earth with the rotation of the small pulley.
- 5. A supporting plate; a supporting plate that can be rotated around the shaft is mounted on the shaft below the large pulley, and the supporting plate is about 50-60 cm long. There is a hole at the right end of the hole, which fixes the shaft of the small pulley in the hole, hangs a suitable elastic belt, and pushes the support plate to make the support plate rotate the earth around the sun. At the same time, the small pulley drives the moon to rotate around the earth.
- Demonstration is required in a shaded room. Push the pallet continuously with your hands, the earth revolves around the sun, and the moon revolves around the earth. You can see the full moon and the lack of the moon. When the earth moves between the sun and the moon, a lunar eclipse is formed; when the moon reaches the sun and the earth Over time, a solar eclipse is formed [1] .