This article refers to the Cart Picket Fence (
and to the Go Direct® Sensor Cart (
Some instructors want students to compare and contrast the data collected using different methods for the same moving object. One way to do this is to use the Go Direct Sensor Cart, a motion detector of some kind, and a photogate of some kind.
While there are a couple of ways to measure the motion of a cart using the photogate, one of the easiest methods is to mount a Cart Picket Fence on top of the cart, and use the Motion Timing mode in Graphical Analysis for an object with 13 flags. However, the Go Direct Sensor Carts were not designed with slots to firmly attach the Cart Picket Fence, and the Cart Picket Fence itself is just a bit too long to fit in the top tray of the sensor cart.
We have found children’s modeling clay is a simple and quick way to mount the picket fence. Students should carefully make sure the picket fence is horizontal with respect to the cart, so that there is no tilt to the stripes that could affect the data.
After finishing the experiment, we recommend removing any clay residue from the picket fence with a soft cloth, such as a rag made from an old cotton t-shirt.