The slope

[Omid]

A football is kicked into the air at some angle theta and lands down field. Ignoring air friction, draw a rough plot of its speed versus time. Is the slope of the curve the acceleration? Explain.

I think the slope of the curve is the absolute value or the magnitude of acceleration, isn't it?

[Pyrrhus]

In graphic of Speed versus time the slope will be instant acceleration or dv/dt

[Diane_]

Cyclovenom is correct, of course. The only addition I would make is that, if you're plotting speed instead of velocity, the slope is going to change sign as you pass through the peak. The acceleration will, of course, be constant, so by taking the slope, you'll be getting the value with possibly the wrong sign. I'm sure this is what you meant by the "magnitude" of the acceleration, so basically: yes, you're right.