One experimental set up that is popular for studying Newton’s Second Law is the Half-Atwood machine. In a Half-Atwood machine, a dynamics cart is tied off to a mass hanging over a pulley. As the hanging mass is released, the cart is accelerated down the track. It is a relatively simple to relate the force exerted on the cart to its acceleration.

When doing a Half-Atwood experiment, it may seem natural to use a Dual-Range Force Sensor (DFS-BTA) to measure force and a Low-g Accelerometer (LGA-BTA) to measure acceleration (or a Wireless Dynamics Sensor System (WDSS, discontinued) to measure both); with each mounted to the dynamics cart, you can easily record both and plot acceleration vs force (or vice-versa). Such experimental set ups, however, often run into a limitation in the Low-G Accelerometer. Because the accuracy of the accelerometer is +/- 0.5 m/s^2 and the acceleration of the dynamics cart in the set up might be as low as 0.1 m/s^2, the recorded data will be extremely noisy. Turning on the “oversampling” option in the data collection parameters may smooth the data out a bit.

In other words, the accelerometer is not the right tool for this particular experiment. There are better ways to measure the acceleration in this context.

A better method would be to use a Photogate (VPG-BTD) with the pulley to calculate position, velocity, and acceleration data. At such low accelerations, the photogate/ultra pulley will produce much smoother data. (The following article may be helpful in setting up the Half-Atwood machine in with a photogate: How do I attach a Smart Pulley to the end of a Vernier Track?) By far, the cleanest data will come from using our Dynamics Cart and Track System with Motion Encoder (DTS-EC); the encoder system measures positions down to the millimeter accurately and produces exceptionally smooth acceleration data.