Module 5: The Universal Law of Mutual Gravitation

The Law of Universal Gravitation was developed by:

c. Newton

Which of these was a contribution of Newton to astronomy?

All of these were due to Newton's work.

How does Newton's Universal Law of Gravitation explain Kepler's laws?

Universal gravitation implies that the planets further from the Sun will move more slowly than the planets closer to the Sun (Kepler's third law), and universal gravitation implies that when a planet is closer to the Sun in its orbit, it will move faster than when it is farther from the Sun (Kepler's second law).

Newton concluded that some force had to act on the Moon because

A force is needed to pull the Moon away from straight-line motion

What does Newton’s Universal Law of Gravitation describe?

The attraction between objects with mass

According to Newton's Law, what would increase the gravitational force between two objects?

Moving them closer together and Increasing their masses

Which scenarios involve gravitational force?

A ball falling from a table and the Moon orbiting Earth

Gravity obeys an inverse square relation. This statement implies that the force due to gravity between two objects

will decrease as the square of the distance between the two objects increases.

True or False: If the mass of a body were doubled, its gravity would become 4 times stronger.

False

True or False: Newton's modification of Kepler's Third Law lets us measure the mass of the Sun.

True

Which of Kepler’s Laws is most directly explained by gravity being stronger when objects are closer together?

Second Law (equal areas in equal times)

Which of the following are true about gravity near the Earth’s surface?

It causes objects to accelerate downward and It changes with altitude

Which statements describe Newton’s contribution to understanding planetary motion?

He described the force causing orbits, He explained why orbits are not circular, and He connected gravity on Earth with the motion of the Moon

What happens to a ball thrown upward on Earth (ignoring air resistance)?

Gravity slows it down as it rises, It stops at the top, then falls back, and Gravity pulls it back down

Orbital velocity depends on:

The mass of the planet and the distance from it

What happens to the orbital velocity of a satellite if it orbits farther from Earth?

It decreases

Escape velocity is best described as:

The speed needed to leave a planet’s gravity completely

Which of the following are required for an object to escape a planet’s gravity?

Sufficient speed (escape velocity) and enough energy to overcome gravitational pull

How are escape velocity and orbital velocity different?

Escape velocity is higher than orbital velocity and Orbital velocity keeps an object moving around a planet

f you were to launch a satellite, which must be true?

It must reach the right orbital speed and It must be placed at the right height

Which changes would increase the orbital velocity needed to stay in orbit?

Moving closer to Earth and A more massive Earth