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## Solving for time

Rate, or speed, is equal to distance traveled divided by time. To solve for time, divide the distance traveled by the rate. For example, if Cole drives his car 45 km per hour and travels a total of 225 km, then he traveled for 225/45 = 5 hours.

## Calculating average velocity or speed

Although speed and velocity are often words used interchangeably, in physics, they are distinct concepts. Speed is calculated by dividing the distance traveled by time. It does not have direction. Average velocity is the displacement (change in position) divided by time.

## What is displacement?

In physics, we love to precisely describe the motion of an object. Seriously, the first few chapters of basically every physics textbook are devoted to teaching people how to precisely describe motion since it is so important to everything else we do in physics.
But to describe an object’s motion, we have to first be able to describe its position—where it is at any particular time. More precisely, we need to specify its position relative to a convenient reference frame. Earth is often used as a reference frame, and we often describe the position of an object as it relates to stationary objects in that reference frame. For example, a professor’s position could be described in terms of where she is in relation to the nearby white board (Figure 1). In other cases, we use reference frames that are not stationary but rather are in motion relative to Earth. To describe the position of a person in an airplane, for example, we use the airplane, not Earth, as the reference frame (Figure 2).
The variable x is often used to represent the horizontal position. The variable yis often used to represent the vertical position.

## Introduction to reference frames

How the choice of reference frame is related to speed and velocity measurements.

## Intro to vectors and scalars

The difference between vectors and scalars. ​Introduction to distance, displacement, speed, and velocity.