Use. with Chapter 2.

Frequently an investigation will involve finding out how changing one quantity affects the value of another.The quantity that is deliberately manipulated is called the independent variable. The quantity that changesas a result of the independent variable is called the dependent variable.

The relationship between the independent arrd deperrdent variable nray not be obvious from simplylooking at the written data. However, if one quantity is plotted against the other, the resulting graphgives evidence of what sort of relationship, if any, exists between the variables. When plotting a graph,take the following steps.

1. ldent i fy the independent and dependent var iables.

2. Choose your scale careful ly. Make your graph as large as possible by spreading out the data on eachaxis. Let each sltace stancl for a convenient antount. For exarnple, choosing thrt-'e spaces equal tolen is not convenient because each space does not divide evenly into ten. Choosing five spaces equalto ten would be better. To avoid a cluttered appearance, you do not need to nurnber every space.

3. Al l graphs do not go through the or igin (0,0). Think about your experiment and decide i f the datawould logically include a (0,0) point. For example, if a cart is at rest when you start the timer, thenyour graph of speed versus time would go through the origin. lf the cart is already in motion whenyou start the t imer, your graph wi l l not go through thc or igin.

4. Plot the independent variable on the horizontal (x) axis and the dependent variable on the vertical(y) axis. Plot each data point.

5. Label each axis with the name of the var iable and the unit . Using a ruler, darken the l ines represen-t ing each axis.

6. lf the data points appear to lie roughly in a straight line, draw the best straight line you can witha ruler and a sharp penci l . Have the l ine gc.r through as many points as possible with approximatelythe sarne number of points above the line as below. Never "connect the dots." lf the points donot form a straight line, draw the best sntooth curve possible.

7. Ti t le your graph. The t i t le ' should clear ly state the purpose of the graph and include the independentand dependent variables.

The graph shown was prepared using goodgraphing techniques. Co back and check each ofthe items mentioned above.

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Elongation versus Force

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