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Horizontal Motion Lesson 1 - Constant Velocity

When dealing with motion, we must first learn some basic terms that we will be using. Distance and Time, represented by and respectively, are self-explanitory, but a term with which some of you might not be as familiar is velocity. Velocity is the rate of motion measured in m/s. Think of velocity as the vector form, meaning it also has direction, of speed.

The first formula for velocity that you will learn is the average velocity formula:
v = d/t = (vo + vf)/2

Let's work with the first part of the formula, , first. This simply means that velocity is equal to distance over time. For example, if a car traveled 10 meters in 2 seconds, the average velocity would be 10m/2s or 5m/s.

As for the second part, , it is just as easy. vo and vf mean initial and final velocity respectively. The words initial and final don't necessarily mean the initial and final velocities of the object in question, but the initial and final velocities of time that the problem covers. For instance, at point A a car is traveling 20 m/s (vo), and further down the road, at point B, the same car is traveling 40 m/s (vf). That does not mean that as soon as the car started it was at 20 m/s, or that 40m/s was the absolute final velocity of the car. It simply means that for the time period of this problem those are the initial and final velocities.

To continue with that example, what is the average velocity of a car with a vo of 20m/s and a vf or 40m/s? Just plug it into the formula. v=(20m/s + 40m/s)/2= 30m/s.

Now, to mix things up a little, we'll combine the two parts into the equation d/t = (vo + vf)/2. Since you already know what everything stands for, let's start with a problem. If a car starts at 0m/s and travels 50m in 5 seconds, what is his final velocity?

Start by identifying the variables.
Do we know d?Yes, its 50m
Do we know t?Yes, its 5s
Do we know vo?Yes, its 0m/s
Do we know vf?No, that is what we need.

Then plug everything into the formula:
50m/5s = (0m/s + vf)/2

And solve for the unknown.
50m/5s = (0m/s + vf)/2
10m/s = (0m/s + vf)/2
20m/s = (0m/s + vf)
20m/s = vf

That's all there is to average velocity. Another term, which does not require much explanation, but does warrant mentioning is constant velocity. Constant velocity is the stable, unchanging velocity at which an object moves. If a problem says that something is moving at a constant velocity, then you can assume that at least vo is what the constant velocity (v) is, if not both vo and vf.

In this lesson, we discusses velocity. The change in velocity is known as acceleration, which we will discuss in the next lesson.