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Superelastic Collisions with the New Vernier Dynamics Cart and Track System with Motion Encoder

Vernier Motion Encoder Cart and Plunger Cart on a Dynamics Track

Dynamics experiments are a core part of many physics courses, and low-friction carts and tracks have long been a popular tool for use with Vernier sensors. Based on customer feedback, we have redesigned our carts and accessories, making a good system even better. Renamed the Dynamics Cart and Track System, the set is available with or without our unique Motion Encoder System, and with either a 1.2 or 2.2 meter track. Additional accessories, such as a pulley and pulley bracket, are also now included—all for an even lower price.

The carts have been redesigned from the axles up. It is much easier to attach sensors and masses to the carts, and, to facilitate classroom discussions, the carts now come in two colors. A new, triggered‑release mode for the spring plunger allows students to set up a superelastic collision between two carts—a collision where the kinetic energy increases. Such a collision still conserves momentum because the plunger spring force is internal to the two-cart system.

To demonstrate the superelastic collision feature, we started with a standard Vernier Dynamics Cart and Track System with Motion Encoder and Long Track, which includes one plunger cart and one encoder cart. We used the optional Motion Encoder Upgrade Kit to turn the plunger cart into an encoder cart. This gave us the ability to track both carts simultaneously, providing excellent position and velocity measurements.

Logger Pro screenshot of superelastic collision

In Logger Pro, we configured the Motion Encoder so that the carts shared the same coordinate system, with the same zero position and positive direction. We started the experiment with the plunger cart at rest, and rolled the plain cart into the plunger cart. On impact, the carts explosively moved apart, with the plain cart reversing direction. The position graph shows the motion clearly, with the cart represented by the blue line rolling into, and then away from, the other cart. Note the complete absence of spikes or other noise in the graph traces, made possible by the Motion Encoder System.

The cart masses were approximately the same (see table). The total kinetic energy of the two-cart system changed by more than a factor of four. The total momentum was essentially unchanged, as expected, because the spring force was internal to the system.

Plain cart* Plunger cart Total momentum Total kinetic energy
Velocity before (m/s) 0.541 0.000
Momentum before (kg m/s) 0.173 0.000 0.173
Kinetic energy before (J) 0.047 0.000 0.047
Velocity after (m/s) –0.514 1.028
Momentum after (kg m/s) –0.164 0.334 0.169
Kinetic energy after (J) 0.042 0.171 0.214
  • * Plain cart mass: 0.3198 kg
  • † Plunger cart mass: 0.3245 kg

In addition to studying superelastic collisions, have students use the Dynamics Cart and Track System to investigate various kinds of collisions, including elastic collisions using magnets as a nearly energy lossless bumper, lossy inelastic collisions using a spring plunger, and totally inelastic collisions using hook-and-pile tabs.

Dynamics Cart and Track System Pricing

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