Velocity and Acceleration

Velocity is the rate of motion or speed in a specific direction. This means that velocity is a vector, we need both its magnitude or value and its direction.

If we only know the speed, that is not the velocity, we have to also know the direction. If we just know we’re going 30 miles an hour that is only our speed. If we know we’re going 30 miles an hour in a southwest direction, then our velocity is 30 miles an hour southwest and that is a vector.

Mini-test: VELOCITY AND ACCELERATION 

Question 1: A man drives 280 miles north in 2.5 hours. What is his average velocity?
A.  
B.  
C.  
D.  
Question 2: Acceleration is the change in
A.  
B.  
C.  
D.  

 

Next Lesson: Electric Force

The transcript is provided for your convenience
Average velocity is one of the two velocities that you need to keep in mind. Average velocity is found by dividing the distance traveled by the time traveled. Your formula would be velocity equals distance over time, so you may start slow, speed up and then slow down as you come to your destination. From point A to point B, how far you traveled is going to be your distance. Let’s say you traveled 120 miles and you were traveling southwest and it took you 60 minutes to get there. Then you would divide that, 120 divided by 60 equals two, so you were going two miles per minute southwest and that would be your velocity, two miles per minute southwest.

Now, if we are trying to do that in hours, we could have just changed it to one hour and that would have been 120 miles per hour, so that is really fast and not a likely velocity. But, if something was going that fast its velocity would be 120 miles per hour one hour southwest or two miles per minute southwest. And it’s important to include the direction, otherwise you’ll only have speed. The fact that you have direction is what makes it velocity. Your average velocity is how far you traveled divided by how long it took overall for the whole trip. Your velocity is constantly increasing and decreasing as you’re traveling.

The other type of velocity to look for is instantaneous velocity and this refers to an object’s velocity at an exact second in time and usually requires the use of calculus to be determined. But, if you hit a pothole it would be good to know if you were going one mile an hour or 60 miles an hour and so knowing at that exact second in time, how fast you were going in what direction that would be important. Sometimes you might have to find instantaneous velocity, but most commonly, average velocity is what you hear about.

Now, acceleration is the change in the velocity of an object. Acceleration is also a vector and will have both magnitude, a value, and direction. Remember we talked about your velocity would be increasing and decreasing as you traveled, acceleration is the change in that velocity Acceleration points the same direction as velocity, while you are maintaining or increasing speed. Velocity is going this direction, acceleration is going this direction, while you are maintaining or increasing speed.

Deceleration is another word for acceleration when you are losing speed, when your velocity is decreasing. Deceleration is going to point in the opposite direction as velocity, so if you’re going this direction, but you’re slowing down, then velocity still points this way. You’re still traveling this way, but your acceleration is decreasing, your velocity is decreasing. When you’re decreasing speed, acceleration is going to go in the opposite direction of velocity. Your velocity is always going to stay the same way because you’re going to be traveling forward in time.

Deceleration is still referred to as acceleration, because acceleration is a vector with magnitude and direction, so it’s going to point backwards, opposite a velocity.
Sometimes the word deceleration is used, sometimes it’s not, sometimes it’s just acceleration both ways. It’s important to know that it can still be called acceleration, either whenever you’re decreasing speed and this is the way that it would look if it was represented with vectors.
To recap:

To recap:
Velocity is your rate of speed in a specific direction. Your average velocity is found by dividing the distance you’ve covered over the time it took you to cover it. Instantaneous velocity refers to an object’s velocity, the exact moment in time. Acceleration is the change in the velocity of an object, either as it increases or decreases. Because acceleration is also a vector and we’ll have both a value and a direction. It will face the same direction as your velocity if you are increasing speed and it will face the opposite direction if you are decreasing speed.

Next Lesson: Electric Force