Archive for January, 2015

Let’s talk Collisions…

I’ve been working on renovating my new house for the last month.  This is moving week.  I feel like being sleep-deprived and tired is no excuse to have a lackluster physics lesson, so I started googling.

First off, I’d like to say that is downright awesome.
I looked at the above car crash web-quest and thought about assigning it to my classes as-is, but I’d like to give my spin.

My physics students were given 5 problems to try in groups of 3.  All collisions involve a car at rest getting rear-ended with both cars sliding forward.  My students are very advanced, but they are still somewhat averse to researching to find their own information.  So I took this basic premise of a car accident and decided to come up with 5 similar problems for the one direction.  The major question remained the same:  Was the driver who caused the accident speeding on impact?

I assumed ideal road conditions and no friction.  To make it more interesting, I looked up celebrities and their various cars to use them as the characters for each story.  Each accident had different sliding lengths and different posted speed limits.  I provided no pictures, just verbal descriptions.  I tried to write my problems like an American news story, so all speeds are in mph, and all distances in feet.

My students needed to use the web to find the approximate mass of the celebrities and their cars, and the braking distance for each car (from 60mph to 0).  From that they could estimate the acceleration applied by the brakes, and work backwards from the sliding distance to find initial velocity following impact.  One the impact velocity was found, the groups could use conservation of momentum to find the velocity of the first car before impact.

I understand that these are pretty idealistic conditions, and that celebrities probably don’t wail on their brakes with perfect reaction time in an accident, but this actually gave my classes even more to discuss!

I also didn’t assign jobs to the students, and was a bit more lax on presentation requirements.  I have one group bringing in lego constructs to re-enact their crash, and another is using posterboards and easels to show the accident and their calculations.

Example problem:

Somebody call the paparazzi! Paris Hilton has been texting while driving again! Thus far she has been able to keep her driver’s license and avoid jail time by using her tremendous wealth to hire the best legal defenses. Unfortunately, she’s been involved in a car crash with another celebrity!


Paris Hilton, driving a 2014 Luxury Cadillac Escalade with 2 wheel drive, rear-ended Justin Bieber’s Ferrari 458 while he was stopped at a Hollywood Boulevard stop sign. The two celebrities were the only people or objects in the respective cars, and the vehicles were presumably brand new.


Justin Bieber is FURIOUS!


The officers have already charged Paris with texting while driving, but if Bieber’s defense team can prove that she was going more than 10 miles per hour over the posted speed limit before impact, then Paris will lose her license.


Police have determined that both vehicles slid in a straight line after impact, and were NOT attached to each other. Bieber and his Ferrari came to rest 78.75 feet past the stop sign, while Hilton and her Cadillac were 6.60 feet past the stop sign. Skid marks at the scene indicate that both drivers applied their brakes at impact until stopping.


The speed limit on this section of Hollywood Boulevard is 30 mph to allow safe travel for sight-seers and pedestrians. Was Paris really going more than 10 miles per hour over the posted limit? It is up to a team of contracted experts (that’s you guys!) to decide.


By picking situations with cars of various weights, my students have been comparing accident results.  What happens when a sports car hits an SUV?  What happens when two vehicles of a similar weight class are involved?  Why are the cops asking physics students to make such harsh decisions?

After the shock of having to do their own research wore off, good times were had.