Johnny Knoxville’s physics, Human Cannonball

The most important thing is that it is the equation of a parable. Looking back at the vertical position data in the video, it seems pretty parabolic at least. Even better, the coefficient in front of t² the term must be a two-fold acceleration. Using parabolic fitting, it gives a vertical acceleration of –11.54 m / s². This is true no expected value –9.8 m / s², but it is very close. (I suspect the length of the cannon can be broken a bit.)

Knoxville’s x and y motions do not match the expected physics. Does that mean the video is real? No, it might still fake yourself, but I personally think it’s real. I mean, doing stupid tricks is a movie like that.

How quickly did he fire from the cannon?

Leaving the Knoxville cannon, it is moving in the horizontal (x) and vertical (y) directions. We already know its horizontal velocity, so we would only need the vertical component of velocity.

However, there is a way to get the full speed (we call it the magnitude of the velocity vector) using the launch angle. Looking at the video and using the portable Tracker Video Analysis tool, it looks like it has a 52-degree angle above the horizontal cannon. Since the horizontal and vertical velocities are perpendicular, I can draw this right triangle:

Since this is a right triangle, I can use the cosine as a relation to the side (v_x) to the hypotenuse (total v). But I know v_x and the angle – that’s it. This puts the overall launch speed at 17.7 m / s (39.6 mph). Yes, it’s pretty fast. It’s slower than a professionally made baseball, but it’s faster than you can run. This launch speed will be useful to answer some other questions.

How far did it go?

The trailer doesn’t show Knoxville’s full movement after firing from the cannon, but it’s okay. We can use the equations of motion of projectiles to solve this distance.

The key to the motion problem of projectiles is that horizontal and vertical movements are independent, except for time. This means I can look at this shooter man and consider his vertical position and vertical speed. I can use that whole time for horizontal movement and I will know where the man has hit the water.