- Vernier's had a Dynamics Cart and Track System for some time. In our revised
version we've taken all we've learned in using those carts and tracks with students
to create a system that's ideal for teaching Dynamics and Kinematics in the
Introductory Physics classroom. Let me walk you through some of the features of
our carts and track. The carts have extremely low friction bearings. There is
an anti-roll peg that keeps the cart from rolling off the lab table when it's simply
placed there. Once you put it in the track and it's free to roll. The ends of the
cart have easily removable tabs where you can keep magnets or hook and pile tabs for
doing different kinds of collisions. The top surface of the cart is well labeled
so that the student can attach sensors such as the dual-range force sensor, the
low-g accelerometer, or the wireless dynamics sensor system. For example I can
take a dual-range force sensor, just place it on the top surface, and the supplied
bolt can be driven in, and now I've attached the force sensor to the top of my
cart, and it's securely in place an d won't shift during the course of an
experiment. The top surface of the cart also includes four mass trays. I can take
a mass, put the mass in the mass tray and change the total mass of the cart without
having to remove my dual-range force sensor. This way a student can do
experiments looking at how the mass of the cart affects the dynamics and kinematics.
Want to remove these and then show you the features of the plunger cart.
Now the plunger cart is a different color. We did this intentionally so that in
discussing collisions, students and teachers will no longer have to say, "this
cart and that cart" or "my left and your right." We can simply talk about the grey
cart or the green cart. The plunger cart is set-up so that you can do a variety of
collisions. One interesting feature is that it's able to do super elastic
collisions where the plunger extends on contact to the two carts. So I can set-up
for a collision between the two carts and have the spring add energy to the system.
I'll let the two drift together slowly and the plunger extends suddenly. It adds
energy to the system. It doesn't change the momentum conservation. There are other
pieces that come with the Dynamics Cart and Track System. For example many times
Physics Instructors want to use a pulley with a photogate attached to the end of
the track, the Dynamics Cart and Track System comes with a bracket and a pulley
so that you can add your photogate and do experiments such as a Half-Atwoods
Machine. The system is available for use both with motion detector, the standard
ultrasonic motion detector or Vernier's unique and innovative motion encoder
system. The motion encoder system has a cart that includes a sensor on the
underside of the cart. That sensor sees the bars that are printed on the top
surface of the track passed by and that information is sent back by an
infrared beam to a receiver at the end of the track. This allows the system to
record the motion of the cart as a function of time very cleanly with no
problems from stray reflections from other equipment in the laboratory. Let's do a
quick experiment showing how a cart on a ramp will work with a motion encoder
system. I'm going to convert this track to a ramp
by removing this foot. Now let's do a quick experiment studying the motion of
the cart as it rolls up and down the ramp. So I'll start data collection in Logger
Pro, give the cart a push, and allow the cart to roll back down and stop it. You
see, very clean data, the position versus time graph shows only the motion of the
cart. There are no extraneous spikes from other things going on in the classroom.
The velocity versus time graph has a nice linear segment while the cart is freely
rolling and the acceleration graph is usable as well showing constant
acceleration as the cart was freely rolling on the ramp. And one thing that
you almost never do in the Physics classroom when you use motion detectors is
talk about the derivative of the acceleration. This is a quantity that's
known as jerk and with the motion detector, you rarely get useful data. I
can change my acceleration graph to a graph of jerk, and let me re-scale that,
and you see that even the third derivative of the position as a function of time is a
useful quantity when collected with a Vernier motion encoder system. The Vernier
Dynamics Cart and Track System is actually an entire ecosystem of Physics education
material. We have additional components that can be used with the carts to study
other phenomenon. For example, I can pull my magnet tabs off of my cart and insert a
friction pad. That friction pad has a piece that roll the rest on the track. And
now I've got a cart moving with additional friction and I can study that phenomenon.
We have other pieces available such as the bumper and launcher kit for doing momentum
impulse experiments. We also have a variety of optics components that attach
to the top of the track. We have thin lenses, we have mirrors, and we have
diffraction apparatus in addition to a color mixing system. So the Vernier
Dynamics Cart and Track System gives the Physics teacher a whole array of equipment
with which to teach first year Physics.