1. Review of Graphing – xy plots
Why do we graph in science?
To see if there is a relationship between 2 variables.
3 most common types of relationships in Physics:
Direct (linear) – a change in the value of one variable causes a similar change in the value of the other
Ex: amount of $ in paycheck vs hours worked
Basic look of graph is a line with a positive slope
generic form: y α x
where α is the proportional sign
Said “y is directly proportional to x”

2. Inverse – a change in the value of one variable causes an opposite change in the value of the other
Ex: price of gas vs how much people drive
Basic look of graph is a hyperbola
Generic form: y α 1/x
Said: “y is proportional to the inverse of x”
or “y is inversely proportional to x”

3. Exponential (power) - as one variable changes value, the other one changes drastically in the same direction
Ex: your physics grade vs amount of class/homework you do
Basic look of this graph is a parabola
generic form is y α x2
Said “y is proportional to x squared”

4. Where do the numbers for x & y come from?
Collected data from an experiment.
independent variable – preset values, prior to running the experiment – on x axis
dependent – measured against the predetermined values of ind. – on y axis
Ex: hours worked & $ in paycheck
ind (on x) dep (on y)
Ex: amt driven & price of gallon of gas
dep (on y) ind (on x)

5. Standard Form of data chart & graph:
data chart : graph: Title: dep vs ind – with more details
ind (unit) dep (unit)
Be sure to:
Decide if (0, 0) should be the first data point – add it to chart and include on graph if yes.
Decide best paper orientation, landscape or portrait and
Decide appropriate intervals for each axis – must be consistent within each axis – to use entire space provided
Provide labels & units on data chart and axes on graph
Draw a best fit curve/line of data points – don’t “connect the dots” – looking for 1 of the 3 relationships
If a line, determine slope from points on the line – ID points used on the graph – included units