# When we graph the relationship between two variables examples

### Relationships Between Two Variables | STAT Scatter plots are similar to line graphs in that they use horizontal and vertical axes to The relationship between two variables is called their correlation. An example of a situation where you might find a perfect positive correlation, as we. Graphing is a pictorial way of representing relationships between various For example, to illustrate how the temperature of the sun varies as one at and analyzing plots of two variables at a time; this means that you'll have two quantities. Graphing a simple linear equation with two variables. usually x and y, requires of a two-dimensional graph representing the relationship between a pair of variables. For example, 4x + 2y = 8 is a linear equation since it conforms to the You may encounter equations with unusually high of low values of.

The closer the data points come when plotted to making a straight line, the higher the correlation between the two variables, or the stronger the relationship. If the data points make a straight line going from the origin out to high x- and y-values, then the variables are said to have a positive correlation. If the line goes from a high-value on the y-axis down to a high-value on the x-axis, the variables have a negative correlation.

A perfect positive correlation is given the value of 1. A perfect negative correlation is given the value of If there is absolutely no correlation present the value given is 0.

The closer the number is to 1 or -1, the stronger the correlation, or the stronger the relationship between the variables.

### How to Graph Linear Equations With Two Variables | Sciencing

The closer the number is to 0, the weaker the correlation. So something that seems to kind of correlate in a positive direction might have a value of 0. An example of a situation where you might find a perfect positive correlation, as we have in the graph on the left above, would be when you compare the total amount of money spent on tickets at the movie theater with the number of people who go.

This means that every time that "x" number of people go, "y" amount of money is spent on tickets without variation.

Using Excel to calculate a correlation coefficient -- interpret relationship between variables

An example of a situation where you might find a perfect negative correlation, as in the graph on the right above, would be if you were comparing the amount of time it takes to reach a destination with the distance of a car traveling at constant speed from that destination. When one collects data one often does not know the exact relationship and interdependence between the various quantities that are being measured.

## Scatter Plots

A graph can give one an idea about how these variables change relative to one another. For this reason you will encounter many graphs in your astronomy courses and in textbooks. For example, to illustrate how the temperature of the sun varies as one moves from the center to the surface and then off the surface, it is best to use a graph as follows: This figure tells us that the highest temperature in the sun is observed to be at its center and that the temperature drops as we go towards the surface.

The graph not only summarizes a lot of detail about how the temperature changes but it also gives us a nice mental image to "hang onto" in order to have some intuitive picture of a process.

• Relationships Between Two Variables

X To start off with, we should look at some very basic graphs. The idea here is to understand what purpose a graph surves. This will make it easier for you to understand all the various plots that you will see presented in class and in your textbook.

## Graphs of Two Variable Functions

Generally, it's a good habit to plot things in science. It works best at explaining what one wants to get across. Plotting is actually an extremely simple idea in its basic form. Here, and in most parts of the courses on basic astronomy, you will be looking at and analyzing plots of two variables at a time; this means that you'll have two quantities.

Let us take an example. Suppose you have measured the apparent brightness of light from a variable star from day to day and have kept track of how the stars brightness changed over time from hour to hour, day to day, or Your two variable are the quantities that you are measuring, namely: The idea behind graphing is to take your data and plot is as points on a set of axes. We usually call one variable the Y-axis and the other variable the X-axis.

These axes are basically two lines that are prependicular to each other as shown here: Notice that Y usually labels the vertical axis and X labels the horizontal axis, and the two axes are always plotted perpendicular to each other.

So, in our example above, we can choose the brightness of the star to correspond to our Y-axis and the time variable to correspond to our X-axis.

The blue curve in the figure reprsents the plot itself. That is, to come up with the blue curve you take each data point - which consists of a time and a brightness value - and you plot that point on the graph with the brightness corresponding to an amount along the Y-axis and the time corresponding to an amount along the X-axis.

You plot all your points and if you have enough number of data points and they are closely spaced you can connect them to form a smooth curve, as the above example figure shows. Lines, Periodic Functions, and More The Line The simplest kind of graphs you will encounter are those in which the relationship between two variables is linear.

Linear relationship simply means that the the the values are related in a way such that if one variable is changed by a certain amount the other variable also changes by a constant proportional amount. We can symbolically write this as: The constant value that relates the changes and makes them proportional is the slope of the line in the graph. A typical linear relationship will look like: Note that there can be different slopes associated with a line, so the above picture is only a shematic representation of a "typical case".

Periodic Functions There are many situations in nature in which some quantity will change periodically with time; an example is the brightness of a variable star that was shown in the plots in the previous section.