Examples of variables are temperature, concentration, surface area, stirring, and crushing. Concentration affects the rate of chemical and physical change. Generally, increasing the concentration increases the rate of chemical or physical change. For example, strong winds increase the burning in a fire. Oxygen supports burning.
Strong winds increase the concentration of oxygen available to the fire.
Strong winds make fighting a forest fire very difficult partly because there is a high concentration of oxygen to support the burning. Fill one clear glass with 1 cup of cold water. Fill another clear glass with 1 cup of hot water. At the same time add one drop of food coloring to each cup. Surface area also affects the rate of physical and chemical change.