How fast was the car going?

Reader Colin asked a great question about this popular clip.

How fast was the car moving?

First, a quick assumption. I will assume that the frame rate on the video is correct (meaning not slowed down). Colin already looked up the length of the Chevy Impala on Wikipedia for me. It has a length of 5.09 meters (I need that to scale the video).

This is the data I get from Tracker Video. The graph below is the x-position of the car with a line fit to the part of the motion before it hit the "ramp". Note that since the car is moving to the left, it has a negative x-velocity.


So, this says the car is moving 24 m/s or 53 mph. Wow. Zooming fast for a toll booth. Notice the speed after the ramp.


That is the same data with a line fit to the part of the motion after the ramp. This gives a x-velocity of 15 m/s or 33 mph. The car slows down because the ramp exerted a horizontal force on it in the direction opposite to the way it was moving. Now, how about the vertical motion?


I don't really have too many data points for while the car is in the air, but fitting a parabola to this data, I get a vertical acceleration of only 1.8 m/s2. That is odd. Let me try marking a different location on the car - this will give me a couple more frames of data. This is from the back end of the car.


This gives a vertical acceleration of about 10 m/s2. That seems better. Here I had a good 4 frames of data using the back end. Notice that the vertical velocity before the ramp is positive. It looks like the back end of the car is coming up as though it were braking. Maybe.

More like this

Clearly, I am not a professional blogger. I am an amateur. This is because I was under the impression that only amateur bloggers could compete in the blogging olympics. When did they change these rules? Anyway, Adam Weiner did a physics-based analysis of the latest Star Trek movie trailer. Here…
If you know me, you know I love Tracker Video Analysis. Basically, it is a free-java program that allows you to get position-time data of a moving object from a video. In Tracker version 3.10, there is now the autotracker feature. This will automagically mark the location of an object moving in…
I enjoyed the super bowl commercials for the most part. You have to be careful not to have too high of expectations, or you will set yourself up for a big letdown. Here is a quick analysis of one of the commercials. This is a Bud Light commercial where at the end they throw a guy out of an…
Through random surfing, I found this clip from The Amazing Race (which is apparently some type of reality show). Don't really know the set up except that it appears some girl is trying to launch watermelons with a slingshot. This looks bad, but she seems to not be seriously injured. Watermelon…

Nice, thank you! :)

The car does veer to the driver's left while in the air so she must have hit it off CoG to the left, so perhaps that is skewing the 1.8 m/s^2?

Hi Rhett,

So many more questions. How high did the car go? How far did it go? How long was it airborne? If it landed on its wheels, with a reasonable assumption of the spring constants of the coil/leaf springs and seat springs, what was the maximum (de)acceleration of the passengers? The car is clearly rotating counterclockwise (when viewed from behind) along its longitudinal axis - given its airborne time, which face of the vehicle hit the ground?

I wouldn't expect answers immediately ;)


If the car was braking, as it has disc brakes in the front at the bare minimum, the front end would likely have dipped instead of lifting up.

By Voodoo Idol (not verified) on 04 Jun 2010 #permalink