CBA Review Forces: Magnetism, Friction, and Gravity

Look at the procedure steps shown for testing a magnet with paper clips. Which step should happen first to start the investigation safely and clearly?

• Lower the magnet slowly toward paper clips

• Hold the magnet high above paper clips

• Measure height when clips stick to magnet

• Measure height when clips begin to move

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Maria rolls a golf ball across flat grass, and it slows to a stop. To compare how friction changes the ball’s motion, what two surfaces should she test next?

• Faster rolling on grass only

• Rolling down a grassy hill

• A smooth surface and rough surface

• Dropping the ball onto grass

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Jack has a marble and a spiral track. Which setup would best test how the speed of a falling object can be changed?

• Change track height and time the marble

• Use the same track height each time

• Roll the marble across a table

• Spin the track without releasing marble

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Look at the photo of sandpaper. Which step would best measure friction between sandpaper and a wooden block during a test?

• Drop the wood onto the sandpaper once

• Glue sandpaper permanently to the wood

• Press sandpaper lightly against the wood

• Hold wood steady and rub sandpaper across it

A horseshoe magnet lifts nails while gravity pulls them downward. Which plan best compares magnetic force to gravity?

• Heat nails and see if they change

• Count nails dropped onto the table once

• Measure nails lifted at different distances from magnet

• Paint nails and watch what happens

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Workers try to move a boulder. Which statement explains how gravity acts on the boulder?

• Gravity stops when boulder touches ground

• Gravity disappears when machines lift boulder

• Gravity pushes upward to keep boulder still

• Gravity pulls downward even when boulder rests

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Alan is experimenting with two bar magnets at home. In one setup, he places the left magnet so that its S pole is next to the N pole of the right magnet. In another setup, he places both magnets so that their S poles are next to the N poles, facing the same direction. What should Alan conclude about how magnet poles affect the force between the magnets?

• N poles always repel while S poles always attract

• N poles always attract while S poles always repel

• The force is always the same in any pole arrangement

• The force depends on how the poles face each other

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Look at the photo of an airplane flying above the clouds. Jerry says gravity is not acting on the airplane while it is in the air. What evidence‑based explanation best evaluates Jerry’s idea?

• Gravity stops in air; only lift pushes the plane

• Gravity still pulls downward; lift and thrust counter it

• Gravity only works near ground; not high in sky

• Gravity acts sideways; engines fight that sideways pull

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A puck slid 80 ft on ice, 35 ft on sidewalk, and 8 ft on grass. Which conclusion best explains the effect of friction on sliding distance across these surfaces?

• Ice has the least friction, grass has the most

• All surfaces have equal friction, so distances match

• Sidewalk has the most friction, ice has the least

• Grass has the least friction, ice has the most

Look at the hourglass photo. Brianne wants the sand to take longer than 2 minutes to reach the bottom. Which change would most likely increase the fall time?

• Hold the hourglass at a slight angle

• Time it in a basement below ground

• Stop watching while the sand falls

• Time it on a skyscraper rooftop