The first buggie lab is used to develop xf=vt+xo directly from y=mx+b. That is exactly why we ask what does the slop represent, what does the y-intercept represent, etc...
Then we do some plots with v vs t graphs and determine area under curve = delta x.
The 2 car buggie lab (one usually has 2 fully charged batteries while the other has 1 battery and 1 slug) is the final lab challenge. For that one, students have had lots of practice using graphs (both y=mx+b for position and area under v vs t = delta x). Kids have their choice of which method they use to determine the intersection point / catching point. If we have the time for different groups to combine and team up to do their own setups, then each team of groups (combining a fast car group with a slow car group makes this new team) whiteboards and presents their setup to the class. If we are short on time, then the class does one setup. Each group can present their method for how they determined the solution.
We usually have a few groups plot to find the point where the two graphs intersect, and maybe 1 or 2 groups each that either use the area under the curves or setting the traditional kinematics equations equal to each other.
The past 3 years I've avoided actually stating the standard kinematics equations until we have used labs to come up with slope of x vs t --> velocity; slope of v vs t --> a; area under a vs t --> delta v; area under v vs t --> delta x.
Then (after at least 5 weeks, which is a long time, I know) we develop general equations from these properties: delta x = vt+.5att; vf=vo + at; xf=vt + xo.
It works very well. It is very time consuming, but it really works well.
Have a good one.
Paul.
From: jbellina [mailto:inquirybellina@comcast.net]
Sent: Thursday, September 19, 2013 7:11 PM
To: Phys-L@Phys-L.org; Paul Lulai
Subject: Re: [Phys-L] motion lab
Do you solve this problems using algebra, or by comparing graphs. You can do some interesting analysis by looking at a straight line graph and then translating it horizontally or vertically. The first thing is to develop an interpretation of the motion represented by the translated graph. In one case the person starts at an earlier or later time, and in the other, the object starts somewhere other than the origin. Then you use these to graphically answer questions like if buggy A goes faster than buggy B, where most Buggy B start the race so it ends in a tie.
Having done it graphically, you can attack it symbolically.
best,
joe
On Sep 19, 2013, at 7:49 PM, Paul Lulai wrote:
Our buggies use 2 C cell batteries. We also replace one c-cell battery with a slug so they run on 1 c battery.
After kids have characterized their buggies we run a challenge with varying scenarios. Basically....
Car 1 starts at this position going that way, car 2 is trying to catch car 1 from behind. Determine where they will meet.
Scenario 2:
Car 1 starts .... car 2 is going to cut off car 1, coming from the other direction like a cop chase scene road block. At what point will the two cars meet (1 going +x, the other going in -x direction).
Have a good one.
Paul.
...::. Sent from a touch screen. .::...
-------- Original message --------
From: Aburr@aol.com<mailto:Aburr@aol.com>
Date: 09/19/2013 6:31 PM (GMT-06:00)
To: Phys-L@Phys-L.org<mailto:Phys-L@Phys-L.org>
Subject: Re: [Phys-L] motion lab
definitely!! Who cares about the speed? But measurement is at the core of
physics.
To add interest
Run a speed competition.
How does an incline (up or down) plane affect the speed?
Battery powered? How does the state of charge affect the speed
If you want statistics you can go into
average
standard deviation
Does one car really run faster than another?
Alex. F. Burr
In a message dated 9/19/2013 2:19:18 P.M. Mountain Daylight Time,
Anthony_Lapinski@pds.org<mailto:Anthony_Lapinski@pds.org> writes:
Is it more about measuring than
finding the actual speed?
Joseph J. Bellina, Jr. Ph.D.
Emeritus Professor of Physics
Co-Director
Northern Indiana Science, Mathematics, and Engineering Collaborative
574-276-8294
inquirybellina@comcast.net<mailto:inquirybellina@comcast.net>