Apologia Physical Science Module 9 Study Guide

Define reference point.

A point against which position is measured

Define vector quantity.

A physical measurement that contains directional information

Define scalar quantity.

A physical measurement that does not contain directional information

Define acceleration.

The time rate of change of an object's velocity

Define free fall.

The motion of an object when it is falling solely under the influence of gravity

If an object's postition does not change relative to a reference point, is it in motion relative to that reference point?

no

A glass of water sits on a counter. Is it motionless?

It is moving relative to many reference points.

A child is floating in an inner tube on a still lake. His position doesn't change relative to a tree on the shore. He watches two girls jog along the shore of the lake. The girls are keeping perfect pace with each other. Neither is pulling ahead nor falling behind the other.

A. Relative to whom is the child in motion?

B. Relative to whom is the first girl in motion?

C. Relative to whom is the second girl not in motion?

A. The child is in motion relative to the two girls. (Event htough the child is floating motionless, his position relative to the girls is changing. Thus, he is in motion relative to the girls.)

B. The first girl is in motion relative to the child. (Since her position relative to the child is changing, she is in motion relative to him.)

C. The second girl is motionless relative to the first girl. (The grils are keeping perfect pace. Thus, their positions relative to each other does not change. They are therefore both motionless with respect to each other.)

A very picky physicist states that it is impossible for any object to experience free fall near the earth's surface. Why is the physicist technically correct?

Air resistance is a second influence (the first is gravity), and all objects experience air resistance.

Even though the physicist that says it is impossible for any object to experience free fall near the earth's surface is technically correct, why do we go ahead and assume that heavy objects are in free fall when they fal near the surface of the earth?

The effect of air resistance is so small on heavy objects that it usually can be ignored.

A long, verticle glass tube contains a feather and a penny. All the air is pumped out, and the tube is inverted, causing the feather and the penny to fall. Which hits the bottom first, the feather or the penny?

Neither will hit first. They both hit together. (Remember, gravity accelerates all objects the same. Without air, there is no air resistance, so both objects are in true free fall.)

A scientist decides to study the acceleration of an object moving in a straight line. He measures the distance of the object at 30-second time intervals. The scientist notices that in each interval, the object travels a shorter distance than it did in the previous interval. Is the direction of the acceleration the same as or opposite of the velocity?

Opposite

equation for finding speed

speed = distance/time

equation for finding acceleration

acceleration = final velocity - initial velocity/time

equation for finding distance

distance = ½ x acceleration x time²

acceleration due to gravity

9.8 meters/second² or 32 feet/second²