Force and Motion

Which of the following objects will have the greatest change in motion?

• A) A small force is applied to an object with a large mass.

• B) A small force is applied to an object with a small mass.

• C) A large force is applied to an object with a large mass.

• D) A large force is applied to an object with a small mass.

Answer explanation

D) A large force applied to a small mass results in a greater change in motion due to Newton's second law (F=ma). The smaller mass accelerates more with the same force compared to a larger mass.

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NGSS.3-PS2-1

Raoul throws a ball into the air and watches it go up for a long time. Then it starts to fall back toward him. What force causes the ball to return to the ground?

• friction

• gravity

• motion

• wind

Answer explanation

The force that causes the ball to return to the ground is gravity. Gravity pulls objects toward the Earth, which is why after reaching its peak, the ball falls back down.

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Arrows represent the forces applied to an object. A longer arrow means a greater force. Which object will move upward?

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When an unbalanced force is applied to an object, the object moves in the direction of the force. Which graph shows how the same force will affect the motion of objects that have different masses?

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NGSS.3-PS2-1

Two boys are about to use the same force to push a parent and a child. Which describes what will happen?

• The parent will swing higher.

• The parent will accelerate faster.

• The child will accelerate faster.

• The parent and the child will accelerate at the same rate.

Answer explanation

The child will accelerate faster because they have less mass compared to the parent, according to Newton's second law (F=ma). The parent and child will not accelerate at the same rate due to their different masses.

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Tori tests how far three identical toy cars travel under three different conditions. How is Tori controlling variables for each trial?

• A) The mass and force change.

• B) Neither the mass nor force changes.

• C) The mass changes, but the force does not change.

• D) The force changes, but the mass does not change.

Answer explanation

Tori is controlling variables by keeping the force constant while changing the mass of the toy cars. This allows her to observe how different masses affect the distance traveled, making option C the correct choice.

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Stefan pushes a cart with three books so it just reaches the end of a track. He puts six books onto the cart. What must he use next time so the cart reaches the end of the track?

• less force

• more force

• the same force

• a different cart

Answer explanation

Since Stefan initially used a certain amount of force to push the cart with three books, adding six books increases the total weight. Therefore, he must use more force to ensure the cart reaches the end of the track.

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NGSS.3-PS2-1

What is one way to improve upon an experiment you have designed?

• by repeating each measurement

• by adding uncontrolled variables

• by trusting his opinions

• by changing data that do not fit

Answer explanation

Ryan can improve his experiment by repeating each measurement, which increases reliability and accuracy. This helps to confirm results and reduce errors, unlike the other options that could introduce bias or inaccuracies.

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Kaneesha pushes a toy truck and lets it roll across a flat surface. She measures the distance it travels. Then she adds different numbers of wood blocks to her truck. Which is most likely the measurement missing from the table?

• 12 cm

• 30 cm

• 57 cm

• 98 cm

Answer explanation

The distance the toy truck travels is likely affected by the weight of the wood blocks. Among the options, 57 cm is a reasonable measurement that suggests a moderate increase in distance due to added weight, making it the most plausible choice.

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NGSS.3-PS2-1

If Alonzo wished to determine how the size of a force affected the motion of an object, which of the following would be the best strategy for his experiment?

• propel several toy cars of different shapes and designs across a surface using a rubber band

• propel a toy car across a flat surface using a rubber band stretched to three different degrees

• propel a toy car across flat and sloped surfaces using a variety of objects, including rubber bands

• propel three toy cars of different masses across a flat surface using a rubber band stretched to the same degree each time

Answer explanation

The best strategy is to propel a toy car across a flat surface using a rubber band stretched to three different degrees. This isolates the variable of force size while keeping other factors constant, allowing for clear observation of its effect on motion.

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