Forces in Equilibrium
Goal: To study the conditions of static equilibrium, to graphically analyze
forces, and to resolve forces into components, both experimentally and
algebraically.
Lab Preparation
According to Newton’s second law, Σ𝑭 = m𝒂, if an object stays at rest, the sum of
the forces acting on it must add up to zero. Such an object is said to be in
equilibrium. The requirement that Σ𝑭 = 0 will be evaluated three ways in this
lab:
1. Experimentally you will find a third force 𝑭3 that balances two other specified
forces by use of a force table.
2. Graphically you will find a third force by adding two specified forces using
the head to tail method (so you might want to review what the head to tail
method is).
3. Resolving forces into components algebraically and experimentally will be the
third way that Σ𝑭 = 0 will be evaluated. Thus you might want to review
Newton’s 2nd law equilibrium problems that use free body diagrams,
components, and summing of forces. Recall that if Σ𝑭 = 0, then Σ𝑭x = 0 and
Σ𝑭y = 0.
Equipment
A circular force table will be used in this experiment (Figure 1). The forces act on
a small metal ring in the middle of the table. Strings tied to the ring provide the
forces. The tensions in the strings are provided by masses hanging over the edge
of the force table.
!
Figure 1
Mass!
Pulley!
Ring!
