Newton's Laws and Gravity

On a scale of 1 (no confidence) to 5 (very confident), how confident do you feel about your understanding of gravity and Newton's laws?

• 1

• 2

• 3

• 4

• 5

What are two factors that affect the force of gravity?

• Mass and size

• Mass and weight

• Size and weight

• Mass and distance

Answer explanation

Gravity increases with mass and decreases with distance. Weight is the force of gravity on an object, and the size of the object doesn't matter -- a big gas planet and a smaller rocky planet would have the same force of gravity if they had the same mass.

Which of these two pairs of objects will have a larger gravitational force?

• The top pair, because they are smaller

• The bottom pair, because they are more massive

• They are the same distance apart, so they will have the same force

Answer explanation

The force of gravity between two objects is larger for more massive objects.

If an astronaut throws a ball in space, what will happen to the ball?

• It will slow down and stop eventually

• It will stop as soon as the astronaut lets go

• It will keep going until it hits something else

Answer explanation

Newton's first law says that objects in motion will remain in motion unless acted on by a force. A ball in space isn't affected by the force of the Earth's gravity or by the force of friction like it would be on the ground, so it continues moving until another force affects it.

What happens if an astronaut pushes another astronaut in space?

• They will both move in opposite directions

• The astronaut who gets pushed will move

• The astronaut who does the pushing will move

• They will both move in the same direction

Answer explanation

Newton's third law says that for every force there is an equal and opposite force -- forces act in pairs. In other words, when an astronaut pushes another astronaut, the same force will be applied to both of them in opposite directions.

Which planet will experience a stronger force of gravity pulling it towards the Sun, Mercury or Pluto?

• Mercury, because it is close to the sun.

• Pluto, because it is far away from the sun.

• Pluto, because it has less mass, so it moves more.

• Mercury, because it is moving faster.

Answer explanation

Mass and distance both affect gravity. Objects that are close together feel a stronger force of gravity. Objects that are more massive feel a stronger force of gravity. Speed doesn't affect the force of gravity.

Why does the Earth orbit the Sun instead of the Sun orbiting the Earth?

• The force of the Sun's gravity is bigger than the Earth's

• The force of the Earth's gravity doesn't affect the Sun

• The Earth is more massive than the Sun

• The Sun is more massive than the Earth

Answer explanation

The Sun is much more massive than the Earth, and so it has a much smaller acceleration due to the force of gravity that pulls them towards each other.

On which planet would you weigh the most?

• Pluto, because it it not very massive

• Earth, because it is where we live

• Jupiter, because it is the most massive planet

• Venus, because it has a very thick atmosphere

Answer explanation

Weight is the force of gravity on an object. Since more massive objects exert a stronger force of gravity, you would weigh the most on Jupiter, the most massive planet.

What is the shape of an orbit?

• Square

• Triangle

• Circle

• Ellipsis

Answer explanation

Kepler's first law states that the orbits of the planets are ellipses, with the more massive object at one of the centers.

If a small asteroid bounced off a larger asteroid, what would you expect to happen?

• Both asteroids would accelerate the same amount

• The smaller asteroid would accelerate more

• The larger asteroid would accelerate more

Answer explanation

When two objects collide, they both experience an equal but opposite force. The less massive object will accelerate more, and the more massive object will accelerate less, because of Newton's second law (Force = mass x acceleration.)