Some everyday examples of equilibrium include: a car at rest at a stop sign, a car moving at a constant speed, two people balancing on a see-saw, two objects at equal temperature, two objects with the same charge density and the population of a species staying the same.
Equilibrium is achieved if all the forces acting on an object are balanced. There are various types of equilibrium depending on whether the context is physical, chemical or biological. An example of physical equilibrium is a car at rest. The force of gravity pulling the car toward earth is balanced by the force of the road pushing the car up. A car at a constant velocity is at equilibrium as well, since the force of friction is balanced by the force from the car's engine. When hot coffee cools down to room temperature, it is said to attain thermal equilibrium with the room since the amount of heat lost by the coffee to the environment balances the amount of heat gained by the coffee from the environment. Chemical equilibrium occurs in reversible reactions when the rate of the forward reaction (converting reactants to products) is equal to the rate of backward reaction (converting products to reactants). An example of biological equilibrium is when the rate at which a species reproduces balances the rate at which the individuals of that same species die.