Supply & demand with elasticity sliders — price controls, deadweight loss, equilibrium
Competitive equilibrium maximizes total surplus (consumer + producer). Price floors above equilibrium create surpluses; price ceilings below create shortages. Both generate deadweight loss — value destroyed that no one captures.
The supply-demand model shows why competitive markets are efficient: at equilibrium, the marginal buyer's willingness to pay exactly equals the marginal seller's cost. Any deviation — price controls, taxes, monopoly — creates deadweight loss: mutually beneficial trades that don't happen.