Gravity and Electricity

Static electricity happens when electrons pass from one object to another, such as from your hair to a comb as you comb your hair. If you then hold the comb near your hair, strands of hair appear to move forward and "stick to the comb." This is because the hair and the comb –

• attract each other because they have opposite charges.

• attract each other because they have the same charges.

• repel each other because they have opposite charges.

• repel each other because they have the same charges.

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Two oppositely charged objects are separated by a small distance. The objects are then moved three times farther apart from each other. Which of the following statements best describes what happens to the electrical force between the objects?

• The force of attraction increases.

• The force of attraction decreases.

• The force of attraction becomes zero.

• The force of attraction remains the same.

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Jupiter is the largest planet in our solar system and has 79 moons that orbit it. The largest four moons, Io, Europa, Ganymede, and Callisto, were discovered in 1609 by Galileo Galilei. These four moons are referred to as the Galilean moons of Jupiter. The moons and their paths around Jupiter are shown below.

What force prevents the Galilean moons from traveling off into space away from Jupiter?

• The Sun’s magnetic pull changes the velocity of the moons.

• The moons’ positions are slightly bent towards Jupiter due to electromagnetic fields.

• The moons are being pulled closer and closer towards Jupiter due to centripetal force.

• Jupiter’s gravitational pull changes the velocity of the moons.

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Each diagram shows two pith balls (foam balls coated with aluminum) hanging from strings. A pith ball can be given a positive (+) or a negative (-) electrical charge. Which of the following diagrams shows a correct way in which the charged balls will be attracted to or repelled by each other?

• 
• 
• 
• 

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How is the weight of an object in a spaceship near the moon related to the distance that the spaceship is from the moon?

• There is no gravity on the moon and therefore they are not related.

• As the distance to the moon decreases, the weight of the spaceship would increase.

• As the distance to the moon increases, the weight of the spaceship would increase.

• The gravitational pull of the moon is constant and therefore the weight would be a constant.

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Steve touched the Van de Graaff generator and all his hair stood on end. The charge from the generator was transferred to Steve's hair so all of the strands had the same + charge. His hairs all repelled each other and stood on end as you see here. This illustrates what law?

• law of gravity

• law of electrons

• law of attraction

• law of electricity

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The moon orbits our Earth. The opposite would never be true; the Earth would never orbit the moon. One reason is due to the force of gravity. The object __________ has a greater gravitational force and that determines what satellites orbit around it.

• with the greater mass
• containing mostly water
• with a thicker atmosphere
• with the greater diameter

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This force is a pull between all objects. It is the force that gives us weight here on Earth. And, if we throw a rock off of a cliff, it is the force that causes the rock to fall to Earth. What is this force?

• gravity

• friction

• magnetism

• air resistance

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The figure shows a negatively charged sphere and a balloon that has been rubbed with dry human hair. If the two are brought close to each other but do not touch each other, you can predict that the objects will

• repel each other.

• charge each other.

• attract each other.

• polarize each other.

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In 1665 Sir Isaac Newton proposed the fundamental law of gravitation as a universal force of attraction between any two bodies. What does this theory state about the force that makes an apple fall and the force that keeps the Moon in its orbit?

• They are unpredictable.

• They are the same force.

• They cannot be compared.

• They act in opposite directions.

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