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Re: [Phys-L] motion lab



Yes. The Modeling approach has the students do constant velocity as either
the first or second lab.
0. They start with no printed instructions, but there is concrete
preparation. There is a brain storming session where the students figure
out the variables that can be "measured". They see the car moving and also
see meter sticks with stop watches on the table.
1. They measure the position vs time for equal time intervals. This is
done by counting 1s ticks or 2s ticks and marking where the car is located.
They have to have 6 data points.
2. The position vs time is graphed and an equation is derived using slope
intercept formulation.
3. The lab must include a motion map as the diagram.
As part of the writeup they have to give the "meaning" of the slope and the
significance of the intercept. They have been told that the name for the
slope on a position-time graph is "velocity" after they have shared results
using whiteboards. The new terms are velocity and motion map.

The brainstorming is an important part of the process because they will
mention all kinds of things that you can't measure, but all are initially
accepted and put on the board. Then I ask if you can measure a particular
variable, or I point out that the size of the wheels is fixed so that will
be held constant... They will say you can measure speed by dividing
distance by time, and I point out that is a calculation, but what can you
use to measure it? They eventually realize we can't. The list of things is
eventually winnowed down to distance (position) and time. They may be asked
how to do this, and eventually if they don't come up with the procedure I
want, I tell them that the fast way is to use the watch to count seconds and
just mark the position on the floor at each second. This can be done with
dry erase markers, or sticky notes. The data run is very fast, and also
makes time logically the independent variable. They have to always list
independent and dependent variables on their labs. I also require them to
make a prediction of what they think the graph might look like before they
do the experiment.

This lab introduces the concept of measurement as distinct from calculation,
motion maps, and the term velocity. It is followed by problems where they
have to use either graphs or motion maps for solution, not just equations.
Also they are hit with the idea that equations must use the actual variables
not X,Y and that the constant in a specific equation must have units. So
they must write their specific equation for the lab as X=3.5cm/s t or
position=3.5cm/s time, but never Y=3.5X. Getting them to give up
meaningless X,Y equations is a constant battle.

John M. Clement
Houston, TX


-----Original Message-----
From: Phys-l [mailto:phys-l-bounces@phys-l.org] On Behalf Of
Anthony Lapinski
Sent: Thursday, September 19, 2013 3:12 PM
To: phys-l@phys-l.org
Subject: [Phys-L] motion lab

Does anyone do a "constant velocity" lab? Like using constant
velocity cars (Tumble Buggies)? If so, what do students
measure (just d and t?)? Do they make a graph? Cookbook or
open-ended? Is it more about measuring than finding the actual speed?

I'm looking for something low tech (for high school) and
meaningful. Just stopwatches and meter sticks. Wanting some
ideas to make a "basic" lab like this interesting...

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