The independent variable is typically the variable being manipulated or changed and the dependent variable is the observed result of the independent variable being manipulated. For instance, In measuring the acceleration of a vehicle, time is usually the independent variable, while speed is the dependent variable. This is because when taking measurements, times are usually predetermined, and the resulting speed of the vehicle is recorded at those times. As far as the experiment is concerned, the speed is dependent on the time. Since the decision is made to measure the speed at certain times, time is the independent variable.

...The independent variable is the variable that is doing the explanation: it is uncaused. The dependent variable is the variable that is caused, or being explained. It is also called the response variable. For example, the price of a car can be expressed as a function of its age. Since age explains (or impacts) the car's price we call it the independent or explanatory variable. Since the car's price is the quantity being explained, we call it the dependent variable, ie, a car's price depends on the car's age.

...To give an example, let's say that you are walking somewhere at three miles per hour.

You can describe this in an equation in terms of y = 3x, where x equals time and y equals distance travelled.

So if you have travelled for one hour, you will have travelled three miles. Two hours, then six miles.

The y variable is called the depedent variable because its value is dependent upon the value of x.

Let's consider a story. You're selling items and $5 an item, where x is the number of items sold, and y is the total money you received.

y=5x

x is the indepent variable, how many items you sold, for it isn't dependent on another number.

y is the dependent variable, total money received, for it is dependent on the independent variable. The value for y depends on the value for x.

The norm is: x is the independent, y is the dependent. x comes first. y depends on x. Whatever variable DEPENDS on the other is the dependent variable.

Does the amount of money earned depend on the number of hours worked? Or does the number of hours worked depend on the amount of money earned?