"Motion of Planets" Gravity and Space Navigation PPT

"Motion of Planets" Gravity and Space Navigation PPT

Part One: Learning Objectives

1. Understand the history of human understanding of the laws of planetary motion

2. Know that observation is an important method to study the laws of planetary motion

3. Know how to draw an ellipse and the characteristics of an ellipse

4. Know Kepler’s laws of planetary motion and the scientific value of Kepler’s laws of planetary motion

Planetary Movement PPT, Part 2: Content Analysis

Understand: What views did the ancients have on the movement of celestial bodies?

Attention: Heliocentrism

(1) The background of the heliocentric theory: At that time, the exploration voyages of Columbus and Magellan had convinced many people that the earth was not a platform, but a sphere.

(2) Copernicus’ speculation: Does the earth rotate around its own axis every day?

(3) Content: He assumed that the earth is not the center of the universe, the sun is stationary, and the earth and other planets move in uniform circular motion around the sun.

Limitations of heliocentric theory:

The heliocentric theory can explain the movement of celestial bodies more perfectly than the geocentric theory, but both theories are imperfect.

Because celestial bodies such as the sun and the earth are all moving, and given the ability to understand natural science at that time, the heliocentric theory was more advanced than the geocentric theory.

Astronomers further study the motion of celestial bodies

1. The exploration of Danish astronomer Tycho:

After Copernicus, Tycho made more careful measurements of the planet's positions for 20 consecutive years, greatly improving the accuracy of the measurements. Before Tycho, the error in measuring the positions of celestial bodies was about 10. Tycho reduced this uncertainty to 2'. A model is derived in which the planets move in uniform circular motion around the sun.

2. Research by German physicist Kepler.

Summarizing all the observational data of his mentor Tycho, during his initial research, the results he obtained were inconsistent with Tycho's observational data. Kepler thought that the error might be caused by the belief that the planets move in uniform circular motion around the sun. Later, he spent four years performing mathematical calculations over and over again. Through calculating this doubt, he discovered the three laws of planetary motion.

Laws: Kepler's three laws

1. Kepler’s first law (orbital law)

The orbits of all planets around the sun are ellipses, with the sun at one focus of all ellipses.

2. Kepler’s second law (area law)

For each planet, the line connecting the Sun and the planet sweeps out equal areas in equal amounts of time.

3. Kepler’s third law (periodic law)

The ratio of the cube of the semi-major axis of the orbit of all planets to the square of the revolution period is equal.

Planetary Movement PPT, Part 3 Content: Frequently Asked Question Types

Question Group 1 Understanding Kepler’s Laws of Planetary Motion

Question 1 [2019·Sichuan Shuangliu Middle School Senior High School Simulation] [Multiple Choice] According to Kepler’s law of planetary motion, which of the following statements is correct ()

A. The planet moves along an elliptical orbit, with the maximum speed at aphelion and the minimum speed at perihelion.

B. The planet moves along an elliptical orbit, with the minimum speed at aphelion and the maximum speed at perihelion.

C. The speed of planetary motion is constant

D. The motion of the planet is a variable speed curve motion

[Analysis] A and C are wrong, B is right: When the planet moves, the line connecting the planet and the sun sweeps out equal areas in equal time, so the speed at aphelion is small and the speed at perihelion is large.

Pair D: The magnitude and direction of the speed of the planet change when it moves, so it is a variable speed curve motion.

【Answer】BD

【special reminder】

(1) Kepler’s laws of planetary motion also apply to the motion of other celestial bodies, such as the motion of the moon (or artificial satellite) around the earth, and the motion of satellites around the planets.

(2) The difference between Kepler's second law and third law: the former reveals the law of the motion speed of the same planet at different distances from the sun, while the latter reveals the law of the motion speed of different planets.

Question 3 [2019·Hebei Cheng'an No. 1 Middle School and Senior High School Examination] For Kepler's law of planetary motion =k, the following understanding is correct ()

A. k is a quantity related to the mass of the planet

B. If the semi-major axis of the earth’s orbit around the sun is a, and its period is T; the semi-major axis of the moon’s orbit around the earth is a, and its period is T, then =

C. T represents the rotation period of planetary motion

D. T represents the revolution period of planetary motion

【special reminder】

(1) The trajectory of celestial bodies is generally an ellipse. The trajectories of some stars (planets, satellites) are approximately circular. For the convenience of analysis, they can be treated as circular orbits.

(2) In Kepler's third law, the k value of all planets rotating around the sun is the same; but the k value is different for different celestial systems. The size of the k value is determined by the central object of the system.

Planetary Movement PPT, Part 4: Content Summary

This section studies Kepler’s three laws of planetary motion. The first law reflects that the trajectory of planetary motion is an ellipse. The second law describes that for any planet, the line connecting it to the sun sweeps out in equal time. over equal areas. The velocity of a planet is minimum at perihelion and maximum at aphelion. The third law reveals the quantitative relationship between the semi-major axis of the orbit and the revolution period. In approximate calculations, it can be considered that the planets all move in uniform circular motions with the sun as the center.

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