### Variables

In order to write the problem, you must be able to identify the manipulated and responding variables. You may choose to complete the controlled variable section after you have decided how you will test your problem.

 manipulated variable (1): the variable that is deliberately changed by the scientist.   You can identify a manipulated variable by asking:

Read the following experiments, then identify the manipulated, responding and controlled variables.  You will not be completing these experiments.

1.  Read the following problem, then determine the variables.  What effect does adding heat have on the temperature of water?

a)  manipulated variable:

b)  responding variable:

c) controlled variables(3):

1. Fill a graduated cylinder with corn syrup.
2. Measure the temperature of the liquid and enter it in the column under "temperature" on the first line of the chart.
3. Pick two marks on the scale of the graduated cylinder to use as reference points, e.g. 40ml and 10ml.
4. drop a steel ball into the liquid
5. Click the stopwatch on when the ball passes the top mark (40ml)
6. Click the stopwatch off when the ball passes the lower mark (10ml)
7. Record your results on the chart
8. repeat steps 4 through 7 until you have completed 5 drops.
 Now repeat the experiment with corn syrup at different temperatures. Use the hot water bath to get it to a higher temperature. Use the ice bath to lower the temperature. source:  http://www.slb.com/seed/lab/viscosity2/index.htm

Determine the variables:

a)  manipulated variable:

b)  responding variable:

c) controlled variables(3):

3.  Examine the following data, then determine the variables for the experiment.

 Amount of boiling water 500 mL Temperature of boiling water 98.5° C Amount of table salt added to boiling water: Run #1 20 g Temperature of boiling water after adding salt: Run #1 101° C Additional amount of table salt added to boiling water: Run #2 20 g Temperature of boiling water after adding salt: Run #2 103° C

a)  manipulated variable:

b)  responding variable:

c) controlled variables(3):

4.  Mary had observed that bean plants seemingly grew taller when Fertilizer A was applied. She decided to conduct an experiment with bean plants to determine which type of fertilizer would produce the tallest bean plants in a 90 day period. She selected three containers of the same exact size and placed the same amount of potting soil in each container. She placed 100 bean seeds in each of the three containers. Each seed was planted the same distance apart in each container. She placed all three containers on the covered back porch. She added FERTILIZER A to one container and FERTILIZER B to another container. SHE DID NOT FERTILIZE THE PLANTS in the third container. She watered the three containers of plants every other day for 90 days. She watered with the same amount of water and distributed the water evenly in each of the three containers. At the end of 90 days, the container of plants receiving FERTILIZER A produced plants with an average plant height of 35 cm. FERTILIZER B plants averaged 25 cm, and the container receiving no fertilizer averaged 20 cm in height.   Determine the variables from the experiment.

a)  manipulated variable:

b)  responding variable:

c) controlled variables(3):