University:
University of Michigan
Course:
PHYSICS 250 | Fundamental Physics for the Life Sciences II
Academic year:

2021
Views:

300

Pages:

2
Author:

apallirasbnc4

Introduction: After establishing that planetary orbits were ellipses, Kepler next looked at the speed of a planet as it traveled around the Sun. Question: How does the velocity of a planet vary as it travels in its orbit? 1. Observe: Place the planet at –5.00i AU and set the velocity to -4.0j km/s (does not have to be exact). Turn off Show vectors. Click Play. Observe the speed of the planet. A. At what point does the planet move fastest? It’s closest to the Sun B. At what point does it move slowest? It’s further from the Sun 2. Observe: Click Reset, and turn on Show vectors. Look at the green vector that represents the force of gravity pulling on the planet. Click Play. A. In which direction does the green vector always point? Go through the Sun B. In which part of the orbit does the gravity vector point in almost the same direction as the velocity vector? It is headed towards the Sun C. In which part of the orbit does the gravity vector point in the opposite direction as the velocity vector? It go away and leaves the Sun 3. Explain: Based on your observations of the gravity vector, why does the planet accelerate as it approaches the Sun and slow down as it moves away from the Sun? The orbital speed varies depending on how far it is when orbiting a planet and how close it is to the host planet. If close, the planet will be accelerated by the impact of the host planet. The example here is the sun and the earth. If the earth gets closer to the sun, our planet will spin faster by the force of gravity. 4. Measure: Click Reset. Imagine a line connecting the planet to the Sun. As the planet moves around the Sun, the line will sweep out an area. Click Play, and then click Sweep area. Record the area below, and then press Sweep area four more times to complete the table. Trial 2 Area (km ) 1 2 3 4 5 18.768 18.768 18.768 18.768 18.768 5. Analyze: What pattern do you notice? I know that number repeats every time I press the result button. 6. Test: Try the same experiment with several different orbits and different numbers of days to sweep an area. Does the same rule hold true for each orbit? Yes it is. Kepler’s second law states that a planet accelerates as it approaches the Sun and decelerates as it moves farther from the Sun. As it orbits, the planet sweeps out equal areas in equal times. 7. Think and discuss: Why do you think the area swept out by a planet in a given period of time remains constant, even as the planet speeds up and slows down? (Hint: Think of each area swept out as a triangle. The height of the triangle is the distance between the planet and the Sun, while the base of the triangle is equal to the distance the planet travels in the given time period.) Since the planets are orbiting in an elliptical shape, sometimes they will be close, sometimes they will be far away. When the planets are close to creasing, the opponent's gravity will make them go faster and when they are far away they will go slowly because gravity is not enough to affect the planet going in orbit. So, the area that the planet sweeps is equal in both cases. because when accelerating, the coverage will be larger and vice versa when decelerating the coverage will be smaller.