A half-Atwood machine, with a cart, string, pulley, and hanging mass, is a common Newton’s Second Law and kinematics lab. If you have a pulley and photogate in this setup, you can easily collect position, velocity, and acceleration data.

Starting in 2016, the Pulley Bracket (B-SPA) includes a special attachment for the Photogate (VPG-BTD). The image below shows how to configure the Pulley Bracket with this special attachment with the Photogate.

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The following video demonstrates how to attach the Pulley Bracket, Photogate, and Ultra Pulley to the track.

Some details to note:

  • The Pulley Bracket comes with two thumb screws. When attaching both a photogate and the Ultra Pulley use the longer thumb screw. If you are only attaching the Ultra Pulley, use the shorter thumb screw.
  • The Pulley Bracket slot allows you to adjust the height of the Ultra Pulley above the top surface of the track. If you are using the photogate/pulley in a half-Atwood setup, lower the Ultra Pulley to a position where the string – connected to the cart on one end and a hanging mass on the other – is parallel to the track; in that position, the force exerted by the string is horizontal, i.e. does not have a vertical component.

If you have a Go Direct® Photogate (GDX-VPG), you’ll find the process a bit easier because the Go Direct Photogate was designed with the pulley bracket in mind, the extra attachment for a photogate was molded into the sensor.

Prior to the 2016 update to the Pulley Bracket, students used the Photogate Bracket (PGB-VDS) to align the photogate beam with Ultra Pulley. The Photogate Bracket has two sides with different tabs. One side is configured for a vertical position for supporting a photogate over the track surface. The other side has tabs for a 45 degree position.

It is this 45-degree position that allows you to easily support a photogate so that it can read the motion of a pulley.

This image shows how to configure the bracket.

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Vernier Photogate (VPG-BTD) Troubleshooting and FAQs