 Now we can introduce the concept of instantaneous acceleration. And that would be the acceleration at a specific instant of time. And we're referring to this compared to the average acceleration which was over a time span. Instantaneous is the default formula, so if you just hear it called acceleration or if you just see the symbol A, they're referring to the instantaneous acceleration. Now when we had average acceleration, we had it represented by the formula that the average acceleration was the change in velocity divided by the change in time. Or if we were going to graph that, it's the two points that you care about which span your time span, and it's the slope of the line connecting those two points on the velocity versus time graph. When you have instantaneous acceleration, we don't have two points to define our slope. We have one, and you can't find slope for a single point. There's two possibilities. If you have a graph where your point is on a straight section of the curve or you could have a graph where your point is on a curved section. When we talk about straight segments, what we're going to look at here is exactly parallel to what we did with the instantaneous velocity. So if you haven't watched that video, this would be a good time to go back and take a look at that one for the details. But our basic concept here is that the whole segment has the same slope, and therefore a whole segment has the same acceleration. So this green segment of the curve is a nice straight line, and we can use the end points of that segment to find the slope everywhere on that segment. So in this case, the time of two seconds is on that segment, and at that time we would have plus two meters per second squared for our acceleration, and the calculations here are exactly parallel to what we did back with velocity. Now if we take a look at this other segment over here that I've now marked in red, it's got a negative slope, and if you were actually to use the end points of the graph, you'd see that any point along there has an acceleration of minus one meter per second squared. And just like we saw with the velocities, anytime you've got a horizontal segment, the slope is zero, so there's no acceleration for that particular segment. If you've got a curved segment, again it's a little bit more complicated. You have to use the slope of the tangent to the curve. Now that's a line which is sort of coming along the graph as if where I'm going to have that thing. And once you've got that tangent down, you can estimate the slope of that tangent line from the graph. Otherwise you need to use calculus to be able to find the slope if you've got a curved segment. So that wraps up our introduction to instantaneous acceleration. If you're going to be doing the calc-based, watch the additional video that explains it in a little bit more detail.