Question

1. summarize keplers three laws of planetary motion. 2. list three of galileos important discoveries. 3. in your own words, list two principles stated in the law of universal gravitation. 4. applying concepts why do we use the mean solar day rather than the sidereal day to measure the time for one earth rotation?

Explanation:

1. Kepler's first law: Planets move in elliptical orbits with the Sun at one - focus. Second law: A line segment joining a planet and the Sun sweeps out equal areas during equal intervals of time. Third law: The square of the orbital period of a planet is proportional to the cube of the semi - major axis of its orbit.
2. Galileo discovered the four largest moons of Jupiter (Io, Europa, Ganymede, and Callisto), the phases of Venus, and observed sunspots.
3. The law of universal gravitation states that every particle attracts every other particle in the universe with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between their centers. Two principles: gravitational force is attractive and depends on mass and distance.
4. We use the mean solar day to measure the time for one Earth rotation because it is based on the Sun's position in the sky, which is more relevant to human daily life and activities such as day and night cycles and timekeeping for practical purposes. The sidereal day is based on the stars and is shorter as it measures the time for Earth to complete one rotation relative to the fixed stars.

Answer:

1. First law: Elliptical orbits with Sun at focus. Second law: Equal - area in equal time. Third law: $T^{2}\propto a^{3}$.
2. Four largest Jupiter moons, Venus phases, sunspots.
3. Gravitational force is attractive; Depends on mass and distance.
4. More relevant to daily life, based on Sun's position for day - night and timekeeping.