Purpose
In this activity, students will measure and interpret the forces acting on an object when the object is in equilibrium.

Discussion
Consider two sign painters who work on a scaffold (a plank of wood suspended by ropes at both ends). They might wonder about the tension in the ropes that support their platform. They are in a state of equilibrium, but how do the forces relate to one another? Their weights are downward forces and the tensions in the ropes suspending the scaffold are upward forces. While the weights of the painters never change, the tensions in the ropes seem to change when the painters move along the platform. In this activity, you will arrange a platform similar to a painter's scaffold. You will measure the forces acting on the scaffold when it is in various arrangements. You will interpret the forces to determine the condition of equilibrium.