Question

1. what causes a planets speed to change as it orbits the sun? 8. summarize keplers second law of planetary motion. 9. what are orbital periods and what standard unit are they measured in?

Explanation:

1. The change in a planet's speed as it orbits the sun is due to the conservation of angular - momentum. As a planet moves closer to the sun (perihelion), its distance $r$ from the sun decreases, and to conserve angular - momentum $L = mvr$ (where $m$ is mass, $v$ is velocity, and $r$ is the distance from the sun), its speed $v$ increases. When it moves farther from the sun (aphelion), $r$ increases and $v$ decreases.
2. Kepler's second law, also known as the law of equal - areas, states that a line segment joining a planet and the sun sweeps out equal areas during equal intervals of time. This implies that a planet moves faster when it is closer to the sun and slower when it is farther away.
3. Orbital periods are the time it takes for a celestial body to complete one full orbit around another body. The standard unit of measurement for orbital periods is the second (s), but for planets in our solar system, years are also commonly used. For example, Earth's orbital period around the sun is approximately 1 year (365.24 days), which is equivalent to about $3.156\times10^{7}$ seconds.

Answer:

1. The change in speed is due to conservation of angular - momentum. As distance from the sun changes, speed adjusts accordingly.
2. A line joining a planet and the sun sweeps out equal areas in equal time intervals.
3. Orbital periods are the time for one full orbit. Standard unit is the second; years are also common for planetary orbits.