Function is an expression, rule, or law that defines a relationship between one variable and another variable. Functions are not only essential in math but even important in physics as well. There are a lot of important and usual events in everyday life that are affected by functions. One of the simplest examples of function in our daily life is the measuring of the temperature and weight while the body temperature or weight is our input and the weight or temperature that we receive from the thermometer or scale is the output. Also we use functions when we want to buy a product or utilize a service. In this case, the price we pay is the input and the product we receive or the service we get is the output. As you can see functions are far more useful than we thought in our daily life and we use them literally everyday without noticing.