Gravity Quiz

Two astronauts are floating in space far away from any planets or stars. What is the direction of the   gravitational force that they experience, if any?

• Toward each other, because there is a gravitational force between them.
• Away from each other because they are pulled by distant planets and stars.
• They experience a gravitational force, but its direction cannot be determined.
• They do not experience a gravitational force because there is no large object nearby.

Astronauts appear weightless in their Earth-orbiting spacecraft because…

• They have escaped Earth’s gravity.
• There is no air in the spacecraft.
• They are moving at the same rate as their spacecraft.
• The spacecraft’s rocket engines counteract gravity. 

The factor(s) that most affect the gravitational force between two objects are:

• size and distance
• mass and size
• density and distance
• mass and distance

Planets A, B and C are identical. A and C have a giant moon orbiting them, while B has a   lightweight artificial satellite orbiting it, as shown in the diagram. Which planet has the strongest   gravitational interaction with its satellite?

• Planet A, because its moon is heavy and close to it.
• Planet B, because only a lightweight object can orbit without falling down. 
• Planet C, because it can interact with a heavy object that is far away.
• All have the same gravitational attraction, because the planets are all the same mass.

Why doesn’t the gravitational pull between the Sun and the planets cause the planets to fall into the   Sun?

• The background stars pull back on the planets. 
• The Sun’s magnetic fields are pushing out.
• The speed of the planets flings them out. 
• The Sun’s rotation pushes the planets out. 

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Satellite B is three times more massive than A, but orbiting the planet at three times the distance.   Compare the force of gravity between each satellite and the planet. The diagram is not to scale.

• A experiences a stronger force than B, because   differences in distance are more influential than   differences in mass.
• B experiences a stronger force than A, because   differences in mass are more influential than      differences in distance. 
• A and B experience the same force, because differences   in distance are exactly compensated     by differences in mass. 
• A and B experience no force, because they are in space.

Assuming the Earth is perfectly round and each person is the same   mass, which person standing on Earth’s surface experiences a   stronger force of gravity? 

• Both A and D, they are near a stronger magnetic field.
• B, he is affected by both the magnetic field and the rotation.
• D, he is at the bottom of Earth and could fall off.
• All the same, they are the same distance from Earth’s center.

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Why does the Earth exert a gravitational force on objects on its surface?

• It has an atmosphere.
• It is very dense.
• It has a magnetic field.
• It has mass.

Suppose the Sun shrank in size but its mass remained the same so that it was compacted much   more densely. What would happen to the size of the Earth’s orbit around the Sun^[i]?

[i] Adapted from a question by Philip Blanco.

• Earth's orbit would get smaller.
• Earth's orbit would get larger.
• Earth would fly out of the solar system.
• Earth's orbit would be unaffected.

Each planet pictured has the same mass M and an identical rocket orbiting at a distance D. The  darker the planet, the denser the material. Which rocket experiences a stronger force of gravity?

• A, higher density means stronger gravity when distance to center of the planet is the     same.
• B, smaller distance to the surface of the planet means stronger gravity when mass of     the planet is the same. 
• Both the same, the stronger gravity from denser planets is compensated by the rocket’s     smaller distance to the surface of the planet. 
• Both the same, each planet has the same mass and the rocket is at the same distance     from the center of the planet.