We will find out later in the module that the force of the string$$s tension pulling on the cart is slightly different than the weight hanging from the string. The reason for this difference will not be discussed at this time. By using the force probe, we can measure the actual force applied to the cart and therefore account for the actual force applied to the cart. In Part $2$ of this module you learned the importance of identifying the object or system before analyzing the effect of forces. What is the system of study in this Exploration?