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Momentum Impulse Experiments with a Photogate

Lots of physics instructors use photogates, but did you know that you can use other sensors at the same time as photogates? For example, you can use a force sensor along with a photogate. You can use this sensor combination in the standard momentum impulse experiment where one measures the velocity of a dynamics cart before and after a force impulse.

We set this up with the following equipment: a Vernier Dynamics System with a track, a cart, a Bumper Launcher Kit (BLK), a Vernier Photogate, and Dual-Range Force Sensor. The BLK includes a variety of magnets and bumpers that can be used to create different impacts. The force sensor is fixed to the track, using the BLK, with a soft, highly Hookean hoop bumper extending the duration of the impulse.

Using either a LabQuest alone or an interface with a computer running Logger Pro, connect the sensors and change the photogate to gate mode, with a flag width corresponding to the flag on your cart. If you use a Vernier Cart Picket Fence it will be 5 cm.

On sending a cart into the hoop bumper, we got these data
On sending a cart into the hoop bumper, we got these data
The integral of the force impulse is 0.485 kg m/s, and the change in momentum is 0.490 kg m/s

The integral of the force impulse is 0.485 kg m/s, and the change in momentum is 0.490 kg m/s.

This experiment can also be done with a Motion Detector, but since you only need the velocities before and after the collision, the extra velocity detail it provides is not needed. The photogate gives just the information you need, with a very simple and reliable setup.

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