In an old thread on this subject I dug up numerous links that support the idea that sliding into first slows you down, but I am not going to dig them up again. To me, it's common sense. Running through the first base bag will be faster than sliding, every time. The only time one should slide into first is if the first baseman has come off the bag, and is trying to apply a tag. A person may feel sliding is faster, but it simply isn't. And yeah, it's more dangerous as well. I guess the stipulation would have to be made that the purpose of the slide is not to slide before you hit the base and stop on it, but to time your dive just right so that you touch the base just as you hit the ground, so the whole "friction of the ground" thing isn't the point. The loss of speed you would have would be from not running optimally for a few steps, but that difference wouldn't be enough to offset not having to travel as far to touch the base. ...and the injury thing kinda makes the point moot, anyways. The problem is that diving doesn't decrease the distance to the bag, just the perception of it. Simply bending forward to position yourself for the dive will put you behind the runner who is running flat out and in stride. The instant you break out of the normal sprinting motion, you lose speed. It's 90 feet from home to first, no matter what configuration your body is in when you get there.