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scientists are detectives

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					Scientists are like detectives!
As science students you must learn how to study or report on things through observation. It is very important that you take notes on everything that you observe. This may include measurements, drawings of what you see, or written descriptions of what you see, smell, hear, etc. Though you may be convinced that you will remember what you did or what happened, write it down in your notebook. Scientists often must record data and wait long periods of time before they have the opportunity to analyze that data. In this lab exercise you will practice making observations, then recording and analyzing your data. 1. Obtain the following items:  30 milliliters (mL) of different milks (skim, 2%, and whole)  2 Petri dishes (you will use both the top and bottom)  Dropper with food coloring  Toothpick in cup with liquid detergent  ruler 2. Prepare the Petri dishes as described in the table below: Petri Dish 1 Petri Dish 2 Petri Dish 3 Petri Dish 4 30mL ‘skim’ milk 30mL heavy cream 30mL ‘whole’ milk 30mL half n’ half 3. Carefully add three drops of food coloring to every Petri dish in a triangle shape as depicted below:

4. Taking care not to disturb the Petri dishes, record your observations. This means draw what you see and describe what the differences are

between Petri dishes. Measure the diameter of spread (distance across) of each drop in every plate (three measurements/plate). Your data table might look similar to the table in step 2 with another row including your observations and measurements. 5. Carefully, let a drop of liquid detergent drip into the center of each Petri dish. Wait several minutes and watch for changes in the food coloring drops. 6. Record your observations as before, including measurements, drawings, and written descriptions. 7. Average the food coloring drop diameters for each Petri dish for both before and after adding detergent. Convert your measurements to millimeters (mM). 8. How are the milk products that we used different? 9. Which kinds of milk did the food coloring spread out the most? a. Why do you think that is? b. How could you test your reasoning to find out if you are correct? 10. How did the detergent affect the diameter of the food coloring drops? a. Based on what you know about detergents (soaps), why would this be? b. How could you test your reasoning to find out if you are correct? 11. Could you have looked at your notes from this experiment two months later and still analyzed the data? If not, you may need to take better notes next time! 12. Make a bar graph of the food coloring drop diameters including all average data points (your teacher will explain this in class). Be sure to include: a. Title b. Labels on X- and Y-axis including units

Challenge!!! Now that you are certified detective-like observers, lets see how good you really are. 1. Pick one peanut from a bag of peanuts to be your special peanut. 2. Get to know your peanut. Just like we did in the exercise above, draw the peanut and anything that makes it different from other peanuts. Your notes to yourself need to be so good that someone else in the room could read them and pick out your peanut from the rest. Do not harm the peanut!!! Remember this is your special peanut, treat it with love and care. 3. When you are finished describing your peanut in your lab notebook, raise your hand for peanut pick-up. 4. When it is your turn, you must be able to find your peanut in the mix. 5. Rate how easily you located your peanut. 1 = easy, no problemo 2 = somewhat easy 3 = found the peanut after much brooding 4 = had to rely on the process of elimination 5 = could not find my own peanut


				
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posted:7/3/2008
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