Definitions and important stuff to know for module 9 (entitled 'An Introduction to the Physics of Motion) in the first edition of Apologia's 'Exploring Creation with Physical Science' text, written by Dr. Jay Wile. Enjoy, and happy studying! -maxacademy

### reference point

a point against which position is measured (position must always be given relative to something else)

### What is the equation for finding speed (equ. 9.1)?

S = d/t

(in which 'S' is equal to speed, 'd' represents the distance travelled by the object, and 't' is the time taken for the object to travel said distance.)

### Speed is either a vector quantity or a scalar quantity?

scalar quantity (it does not contain directional information)

### Velocity is either a vector quantity or a scalar quantity?

vector quantity (because it includes direction)

###
Copy this statement and fill in the blanks (you can ignore stuff in parentheses and not have to type out the whole thing):

When objects travel in the same direction, their relative speed is the __________ between their individual speeds. When they travel in opposite directions, their relative speed is the __________ of their individual speeds.

(When objects travel in the same direction, their relative speed is the) difference (between their individual speeds. When they travel in opposite directions, their relative speed is the) sum (of their individual speeds).

### acceleration

the time rate of change of an object's velocity (typically expressed in meters/second²)

### How do we find the acceleration of an object (equ. 9.2)?

A = f - i / t

(in which A = acceleration, f = final velocity, i = initial velocity, and t = time. If using meters/second for the velocities, you will typically get the answer in meters/second/second, or meters/second².)

### What's the acceleration due to gravity in meters/second²? What about feet/second²?

9.8 meters/second²

32 feet/second²