If you need to bring anything to do your experiment next time, decide who will bring the necessary materials or equipment.

Make a data sheet to collect the data during your experiment next time. The data sheet should include places to record the

• names of each student in the group

• resting heart rates (pulse counts) for each subject before the stimulus or activity, as well as the heart rates during and/or after the stimulus or activity

• anything you notice which might affect the results, for example, other things which may be happening in the room during your experiment or changes in each subject’s mood during the experiment.

If you complete these activities before the end of the period, you can begin the Hypothesis and Methods sections of your poster. (See below.)

Part 2

Doing Your Heart Rate Experiment

Review your experimental plan from last time, and carry out the experiment for each subject in your group. Record your data in the data sheets that you prepared.

Analysing Your Results

Discuss the best way to analyse your data in order to test your hypothesis. You may want to use one of the following methods of analysis.

(1) For each subject, calculate the difference between the resting heart rate and the heart rate during or after the stimulus or activity. Make a table which shows these change in heart rate values. Calculate the average change in heart rate for all subjects in the experiment, and record this average in the table.

(2) For each subject, graph the resting heart rate and the heart rate during and/or after the stimulus or activity. Calculate the average resting heart rate and the average heart rate during and/or after the stimulus or activity. Graph these averages. Be sure to label both axes of any graph that you make.

Each student should analyze the data and attach the table or graphs you have prepared.

Do your results support your hypothesis? What conclusions can you draw from your experiment?

Poster

Each group should prepare a poster on their heart rate experiment. This poster should explain your hypothesis, the basic procedures you used, your main results (summarized in a graph and/or table), and your conclusions.

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Each time the heart beats, blood is pumped into the arteries. As the blood surges into the arteries during a heart beat, each artery stretches and bulges. This brief bulge of the artery is called a pulse. You will be measuring heart rate by counting the number of pulses in the artery in the wrist in a 30 second interval.

To feel the pulse, find the artery in your partner’s wrist. Place the tips of the first two fingers of one hand on the palm side of your partner’s wrist, over toward the thumb side of his or her wrist. You may need to press quite firmly in order to feel the pulse of blood which each heart beat sends through the artery. Don’t use your thumb to feel the pulse in the wrist, because your thumb has a pulse of its own.

To measure heart rate, count the number of pulses in 30 seconds. Multiply that number by 2, and you will have the number of heart beats per minute.

After you have practiced taking heart rate, it is important to check the accuracy of your heart rate measurements. Work in a group of four using the following procedure to test and improve the accuracy of heart rate measurements.

Due to a discussion we had with another school we have looked out how our Hear Rate experiment was not held under the right conditions. We are planning to re-test this in a controlled environment, as outlined by the other school.

One student in the class is a keen and accomplished athlete and trains 5 to 6 times a week and her heart rate turned out to be by far the lowest (graph below) before the exercise and was quickest to return to normal after the exercise routine.

When the heart beats, a pressure wave moves out along the arteries at a few metres per second (appreciably faster than the blood actually flows). This pressure wave can be felt at the wrist, but it also causes an increase in the blood volume in the tissues, which can be detected by a plethysmograph. This word comes from the Greek “plethysmos” for increase and is a term for a “fullness” (ie change in volume) measuring device. Over the years, all sorts of Heath-Robinson devices have been used but described here is a photoelectric pulse plethysmograph, which is robust and easy to make and which will allow the beating of the heart to be recorded without the need to make direct electrical connections to the body.

Transition years investigated the effect of exercise on heart rate using a heart rate sensor. The students took it in turns to measure their heart rate before and after a short exercise routine. This proved the least successful of the investigations as it was necessary for the students to remain calm to obtain consistent results. With only one heart rate sensor the girls had to use it in turn and were easily distracted by what was happening elsewhere in the class causing inconsistencies.

After collecting our finds we gather the data and created a graph with our school computer. The findings really show some interesting results and allows us to understand the basic principles of pressure and the general atmospheric pressure surrounding us at all times.

5^th year students used the pressure sensor to prove Boyle’s Law. Results and graphs were very good apart from the occasional “blip” due to difficulty in maintaining pressure at low volumes. The pressure sensor was also used as a simple barometer to measure atmospheric pressure for the volatile liquid experiment.

We felt that the hands on practice of doing this experiment was invaluable. Actually creating a barometer for real helps you understand so much more than reading it in a book.

This class also used the temperature sensors to investigate the radiation of heat from shiny and dull surfaces. Good results were obtained showing loss of heat through radiation but results for the absorbance of radiated heat were not any more obvious than the thermometers. The students themselves suggested the increase in temperature was too small to be noticeable. The use of Bunsen burners as a heat source may also have been a factor.