A classic experiment in physics is the Atwood’s machine: two masses on either side of a pulley connected by a light string. When released, the heavier mass accelerates downward while the lighter one accelerates upward at the same rate. The acceleration depends on the difference in the two masses, as well as the total mass.

In this lab, you will determine the relationship between the two factors that influence the acceleration of an Atwood’s machine using a Photogate to record the machine’s motion.


  • Use a Photogate to study the acceleration of an Atwood’s machine.
  • Determine the relationships between the masses on an Atwood’s machine and the acceleration.