7.2MechanicsStretch
Modelling with Statics
Real situations — a hanging sign, a suspended mass, a sloped support — are modelled with static equilibrium. The skill is drawing a clear force diagram and choosing helpful directions to resolve in.
What you'll be able to do
- Draw a force diagram for a model
- Identify all forces acting
- Choose convenient resolving directions
- Solve the resulting equations
1
Building the model
Start with a force diagram showing weight, tensions, reactions and any applied forces. Then resolve in directions that make the algebra simplest — often along and perpendicular to a string or slope.
Modelling workflow.
1Weight downward, two tensions along the strings.
2Resolve horizontally and vertically; set each to zero.
AnswerWeight + two tensions; ΣF = 0 in two directions.
Tip — Choose resolving directions along unknown forces to simplify the equations.
Formula recap
Equilibrium of the model.
Weight of a mass.
Common mistakes to avoid
Omitting a force from the diagram.
Include weight, tensions, reactions and applied forces.
Always resolving horizontally/vertically even when awkward.
Resolve along the most convenient directions.
Key takeaways
- Draw a complete force diagram first.
- Resolve in convenient directions; set ΣF = 0.
- Weight of a mass is W = mg.
Test yourself
Ready to lock in Modelling with Statics? Pick a mode and earn XP & Dobloons.