HP Cycle 31

Today, we'll design a lab where we'll use physics from several past units to investigate car crashes.  Here is the situation:

The Forensics Lab of the New York City Police Department is interested in learning how to determine the coefficient of friction between two surfaces – the tires of a vehicle and the road. They need this information to help them relate the length of the skid marks to the speed of a vehicle before it started skidding. Your group, as a part of an interview process for a lucrative contract with the NYPD, is asked to devise a procedure to determine the coefficient of friction between the tire rubber and the asphalt using a collision process. They also asked you to write a detailed report about the experiment so they can replicate it. 

You come up with the following experiment as simplified model of the collision: Using a track and the spring-loaded plunger of a dynamics cart, you launch the cart towards a stationary wooden friction block. The cart and block collide and, with the use of velcro, stick together and slide to a stop. This process resembles a collision between a car in motion and a car at rest. The distance that the carts slide on the track represents the distance the cars skid after the collision. 

Your goal today is to come up with the mathematical model that will help us find the coefficient of friction between two surfaces.  You've done this two other ways before, and this time,  you'll design a third method using limited resources:

• track

• plastic dynamics cart with spring plunger

• wooden friction block

• meter stick

• protractor

• mass balance

• brick

• track ring stand support

• spring scale (for verification experiment only)

We'll have brainstorming time today.

Also, today, you will fill out a form in ✏️ Google Classroom with your goals as a "Collaborative Team Member" during this group activity.  At the end of the project, you will be doing a self-evaluation of your collaboration based on this Collaborative Team Member Rubric.  Also read through the Scientific Abilities Rubric which you will be completing by the end of the project.

Handout:  Collaborative Team Member Goals & Self-Evaluation

Printable Version of Forensic Physics Lab:  Forensic Physics Lab

Homework:  Make sure the ideas of what you're going to do in lab are clear in your mind.  Also, make sure you've read through the two self-evaluation rubrics:  Collaborative Team Member Rubric and Scientific Abilities Rubric.

Today, we'll use class time to finalize ideas for the forensic physics activity.  Last time, you should have come up with an idea for how you will design the model.  In your group today, you'll be collaboratively creating what you think will be the best mathematical model that the police could use to investigate car crashes.   If we get to it, having already created a mathematical model of the car crash, you will use a physical model to take data for the Forensic Physics Lab.  

You'll take your lab data and do your final analysis.  You need to run trials with different conditions.  You should ultimately have a graph with three or four data points.  Linearize the graph if necessary.  How do you extract the coefficient of kinetic friction from the best fit line?  You should not be finding the coefficient using particular data points and averaging!  That is not the way we do science!  

Homework:  If you have not completed testing your mathematical model with a physical model, then make sure you have a really good plan to do this at the beginning of next period.