Forces, Energy, and Motion

Some forces act at a distance. Other forces act only when two objects are in contact with each other. Which of the following force can act across a distance?

• Friction

• Electric

• Mechanical

• Normal

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Matthew is trying to push a large box across the gym. Although Matthew is exerting a force, the box does not move. What keeps the box from moving even though Matthew is pushing on it?

• The normal force is pushing against Matthew’s force

• The force of gravity is opposed to the force exerted by Matthew

• The equal and opposite force of friction prevents the box from moving

• The force exerted by Matthew on the box is not in the right direction to move the box

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Chamber P is filled with air while chamber Q has no air in it. If a leaf and a brick are dropped from the top of each chamber at the same time, where will they hit the ground at the same time?

• In chamber Q only

• In chamber P only

• In both chambers

• In neither chamber

Suppose you were to fill a balloon with air then let go of it without tying it closed. What causes the balloon to fly away?

• Your breath contains helium, which is lighter than air

• The air around the balloon is under higher pressure, so it pulls the balloon forward

• The warm air from your breath is less dense than the cooler air around the balloon, and warm air always rises

• The balloon’s movement is the reaction to the force of air escaping

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Two airplanes are flying in the sky in such a way that the gravitational attractions between them decreases. Which statement best describes how the planes must be flying?

• Away from each other

• Next to each other at the same speed

• Towards each other

• Faster than the speed of sound

Your weight on the moon is about one-sixth of your weight on Earth. Why do you weigh less on the moon?

• The moon has more gravity because it is smaller than Earth

• The moon has more gravity because it is closer to Earth than the sun

• The moon has less gravity because it has less mass than Earth

• The moon has less gravity because you are closer to its center than on Earth

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The objects shown in the following diagrams have different masses and are different distances apart. Which diagram shows the two objects that have the greatest force of gravity acting between them?

• A

• B

• C

• D

High and low tides are the regular pattern of rising and sinking ocean-water levels. They are caused when the sun’s gravity and the moon’s gravity pull on ocean water. The moon’s gravity has a greater effect on Earth’s oceans than the sun’s gravity. Why would the moon have a greater effect than the sun?

• The moon is not as hot as the sun

• The moon has less mass than Earth

• The moon has less mass than the sun

• The moon is closer to Earth than the sun

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If to objects are moved farther apart, how would the gravitational attraction between them be affected?

• The gravitational attraction between them would decrease

• The gravitational attraction between them would increase

• The gravitational attraction between them would remain the same

• The gravitational attraction would change for the large object but not for the smaller one

A rocket burns fuel to create hot gases that explode violently out of the rocket engine. This explosion creates thrust. Thrust is a force that pushes the rocket upward. What force must thrust overcome in order to send a rocket up into space?

• Gravity acting on the exploding gases

• Gravity acting on the rocket

• Friction between the rocket and the ground

• Friction between the rocket and the exploding gases

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