What Does a Variable Mean in Science?

• Variables should be measurable.
• Control variable(s) should be constant.
• Dependent variables are dependent on independent variables.

Scientific learning has become a part of our daily life; it's no more a scientist's domain restrictive to big laboratories and fancy instruments. Science experiments are performed in high schools for science fair projects, or even by toddlers when they are curious about their surroundings and are getting to know new things.

Experiments are vital to practical science; any theory or hypothesis can be proved only through these investigative studies. An experiment helps in establishing a relation between the cause and effect that various parameters have on a particular system.

There are various components and parameters that are present in a system, and a change in one or all them will have an impact on the entire system. These are termed as variables.

Any particular element, factor, or a component present in a system, which when changed can result in a predictable variation in the system, is termed as a variable. A variable comes into play in science, usually as a part of some form of an experiment. Changes can be brought in a variable or it can be manipulated as a part of the experiment.

The different types of variables are:

• Control Variable
• Independent Variable
• Dependent Variable

A variable that remains unchanged to the completion of an experiment is known as a control variable. Its value remains the same until the experiment establishes some relation between the other variables. Also, this variable can be controlled by the user.

An independent variable is the one that does not vary according to any other parameter in the experiment. People who conduct experiments have control over the variations in these variables and can introduce changes in them to observe the effects on the system.

A dependent variable is the one that is dependent on the independent variable. These variables are not under the control of the observers since their values change according to variations in the independent variables.

An experiment establishes a relationship between a dependent and an independent variable, and the following examples will give a clear understanding of the same.

Consider a simple experiment to find out the effect of water on the growth of plants. Take two plants, plant A and plant B of the same type for this experiment. Use the same source of water for watering these plants. 

Feed these plants with different quantities of water from a common water source. As a result of the changes in amounts of water that is supplied to the plants, their growth will not be the same. In this case, the source of water remains the same throughout the experiment. The water source thus is a control variable.

Each plant is watered with different amount of water. This makes the quantity of water that each plant receives an independent variable, whereas the growth of these plants becomes a dependent variable since it depends upon the amount of water the plants are provided with.

➤ Control variable: Source of water, sunlight, fertilizers, size of pot etc.
➤ Independent variable: Quantity of water
➤ Dependent variable: Growth of plants

Take into consideration the Ohm's law, which can be represented as,


Where,

V = the voltage or the potential drop
I = the current that flows across the circuit
R = the resistance offered by the circuit to the current flow

The resistance of a circuit remains unchanged throughout the course of the experiment, hence it is the control variable. The current flowing across the circuit will vary according to the applied voltage. 

Thus, voltage is a variable that the user can control, and therefore, it is an independent variable in this experiment. On the other hand, current flowing across the circuit changes with the changes in the voltage, and hence, it is a dependent variable in this experiment.

➤ Control variable: Resistance
➤ Independent variable: Voltage
➤ Dependent variable: Current

Consider an experiment that finds out if heating water makes it possible to dissolve more sugar. In this example, the amount of water used is constant to the end of the experiment, and thus, it becomes a control variable in this experiment. 

The temperature that is used to heat water can be controlled by the person performing this experiment, and so, it is an independent variable in this case. Since the amount of sugar that dissolves in water will vary according to the temperature, it is a dependent variable here.

➤ Control variable: Water
➤ Independent variable: Temperature
➤ Dependent variable: Amount of sugar dissolved

In an experiment, the effects of varying voltage on the speed of an electric motor are to be determined. Here, the electric motor that is used will remain unchanged which is the control variable in this experiment. The voltage applied to this electric motor is controlled by the users and is changed to establish the required relationship. 

Thus, it is the independent variable in the experiment. On the other hand, the speed of the motor is an outcome of the applied voltage, so it becomes the dependent variable in this case.

➤ Control variable: Electric motor
➤ Independent variable: Voltage
➤ Dependent variable: Speed

Take an example to find the amount of water that runs through a faucet when opened at different levels (half open, full open, closed). Here, the type of faucet used is constant to the completion of the experiment, and thus, is the control variable. 

The opening level of faucet that the user can control is the independent variable in this experiment. And finally, the amount of water that flows through the faucet relies on the opening level of faucet, and hence is a dependent variable in this experiment.

➤ Control variable: Faucet
➤ Independent variable: Faucet opening level
➤ Dependent variable: Amount of water flowing through the faucet

A variable can also be introduced in the system to represent a quantity in an ongoing task that is unknown to the observers. This way variables do come handy in science experiments.