 Now, we introduce the concept of speed as it's used in physics. In general, speed is a measure of how fast is an object moving. It's always a scalar quantity, meaning direction doesn't matter, how fast I'm moving, but not which way. It always has dimensions of type length divided by time, length over time, and that means it's got a standard metric unit of meters per second. But again, any length per time is an acceptable use, including miles per hour. There's two different types of speed that we're going to take a look at. One is the average speed, and the other is the instantaneous speed. Average speed means how fast, on average, was an object traveling during a specific time period. Instantaneous speed is how fast is an object moving at a single specific time. When it comes to average speed, we can calculate it using this formula. Speed average is the distance divided by the time. This is sometimes noted using a V with a subscript of A, V, G for your average speed, D for the distance, and delta T, where again, delta means the change in to give us our time span. Instantaneous speed is the magnitude of the instantaneous velocity. So since velocity is a vector, the speed is the magnitude of that. And if we remember our vector notation, the parallel bars here tell us that we're looking at the magnitude. The line above says this is the vector, so that's the velocity. And the quantity that does not have a vector sign over it, that's the scalar magnitude or the speed. This just introduces you to the basic concept of speed as we're using it in physics. You'll have a lot more examples of actually calculating these as we move through the semester.