Excerpt from “The Relative Motion of the Earth, Moon, and Sun” Lesson Plan
o Write on the board: “Relative Motion” and “Motion of the Earth, Moon, and Sun”. o Begin by telling the class that you are going to “blow a hole in what they know” and fill it with new knowledge. Explain “there are some things in science you probably think you know, but you don’t know everything.” Ask, with a show of hands, “Who knows how the Sun, Earth and Moon move?” o Ask a volunteer to draw on the board the motions of the Sun, Earth, and Moon. o They will probably draw a diagram that looks similar to this: [pic]
Remind the students that these “paths” are called orbits, they are a result of gravitational pull and orbital velocity, and all of the orbits are counterclockwise. o Explain that this diagram is one way to think about the motion of the Sun, Earth, and Moon, and it is not wrong, but this diagram does not tell the entire story. Relative Motion
o Discuss relative motion. How do we know that something is moving? Show video disc of two trains and a man walking on a boat close to shore. Write on the board “All motion is relative to whatever frame of reference is chosen, because there is no motionless frame.” Discuss, asking the following questions: 1) What is a frame of reference? (A frame of reference is a set of reference points with respect to which motion is measured. These points move together and keep their relative distances and angles of view. Examples include interior of a house, a ship, airplane, car, railcar, spaceship, surface of the Earth, a moving elevator, a river carrying a swimmer) 2) Why is there no motionless frame? (There is nothing in the Universe that is not moving) 3) What frame of reference do we usually use when we are describing motion? (We use the surface of the Earth.) Give the following example where we have 2 different frames of reference: Frame of reference A is the inside of an elevator rising with constant velocity u, while frame of reference B is the outside of the building in which the elevator is located. Is the velocity of the penny the same as seen from A and B? No, in A the penny looks like it is falling down, while in B the penny is actually moving up with respect to the building. Motions of the Sun and Earth
o Tell the students that first of all we will talk about the motions of the Sun and the Earth. o Ask the students, “Does the Sun move? How do we know?” Students might answer that they see the Sun moving across the sky every day, but they should be asked, how do we know that the Sun is moving around the Earth and not vice versa. This can be explained by looking at how the Sun’s diameter changes during different parts of the year, by the changing locations of the stars, by applying some of Kepler’s laws and understanding gravity. We will have touched on this when we learned about the different historical models of the universe. o Explain that the Sun rotates every 27 days at its equator ( How do we know? We have watched the location of sunspots) and moves through the universe at 19.7 km/sec (44,000 mph) as it revolves about the Milky Way galaxy. It is tilted at a 25 degree angle and headed toward the Hercules constellation. This is the Sun’s motion relative to the other stars in our galaxy. o Model the Earth’s and Sun’s motions using the grapefruit and lime. Show the Sun (grapefruit) moving linearly through space with one hand, while the Earth (lime) moves around the Sun. Ask the students, “Do you still think the Earth moves in a circle around the Sun?” Confirm that the Earth moves in a spiral around the Sun relative to the other stars. o Discuss the limitations of this model, namely the incorrect distance and sizes represented between the Earth, Sun, and Moon. Why then do we use this model? Although this model is incorrect in some ways, it is still...