### Review Questions

State Kepler’s three laws in your own words.

Why did Kepler need Tycho Brahe’s data to formulate his laws?

Which has more mass: an armful of feathers or an armful of lead? Which has more volume: a kilogram of feathers or a kilogram of lead? Which has higher density: a kilogram of feathers or a kilogram of lead?

Explain how Kepler was able to find a relationship (his third law) between the orbital periods and distances of the planets that did not depend on the masses of the planets or the Sun.

Write out Newton’s three laws of motion in terms of what happens with the momentum of objects.

Which major planet has the largest . . .

- semimajor axis?
- average orbital speed around the Sun?
- orbital period around the Sun?
- eccentricity?

Why do we say that Neptune was the first planet to be discovered through the use of mathematics?

Why was Brahe reluctant to provide Kepler with all his data at one time?

According to Kepler’s second law, where in a planet’s orbit would it be moving fastest? Where would it be moving slowest?

The gas pedal, the brakes, and the steering wheel all have the ability to accelerate a car—how?

Explain how a rocket can propel itself using Newton’s third law.

A certain material has a mass of 565 g while occupying 50 cm^{3} of space. What is this material? (Hint: Use Table 3.1.)

To calculate the momentum of an object, which properties of an object do you need to know?

To calculate the angular momentum of an object, which properties of an object do you need to know?

What was the great insight Newton had regarding Earth’s gravity that allowed him to develop the universal law of gravitation?

Which of these properties of an object best quantifies its inertia: velocity, acceleration, volume, mass, or temperature?

Pluto’s orbit is more eccentric than any of the major planets. What does that mean?

Why is Tycho Brahe often called “the greatest naked-eye astronomer” of all time?