Practicing in Measuring

1. Practicing in Measuring Volume, Mass and Length

2. Volume • Graduated cylinders Glass Plastic Clear fluid problems Procedure for finding volume of irregular objects • Burettes and Pipettes • Beakers

3. You should be able to measure the volume of liquids in a graduated cylinder. How precisely you can measure volume depends on the size and type of graduated cylinder you use. Generally, you should be able to estimate between the etched or printed lines.

4. On this 100 milliliter cylinder, the numbers are 10, 20, 30, etc., so there is a 10 milliliter increment between them. Since there are 10 divisions between consecutive numbers, each division represents one milliliter. Therefore, you should be able to estimate to tenths of a milliliter by reading between the lines.

5. It is important to notice what each line or interval on the graduated cylinder represents. Different kinds of graduated cylinders are set up differently. A 10 milliliter cylinder, for example, usually has one tenth of a milliliter for each graduation, but some have two-tenths milliliter for each graduation. The way to check this is to count the divisions between consecutive numbers. 8.8 mL

6. On some cylinders, there may only be five divisions between numbers. Or there may be ten divisions for a 2 milliliter increment. In these cases, each of the divisions represents 0.2 milliliters, rather than 0.1. You need to be aware of that when you're using the cylinders like these, and adjust your between-line-estimates accordingly.

7. ? We need to see the rest of the graduated cylinder to know what increments these lines are in.

8. A characteristic of liquids in glass containers is that they curve at the edges. You measure the level at the horizontal center or inside part of the meniscus. Read the bottom of the meniscus. 5.9 mL

9. 6.8 mL

10. In some plastic cylinders water has a flat surface. In that case top or bottom doesn't matter, but we can still say use the center rather than the edges. ~ 293 mL

11. The visibility of the meniscus can be enhanced by using a card with a dark stripe on it,  placed behind the cylinder.  Adjusting the placement of the card can give you either a white meniscus against a black background or a black meniscus against a white background. ~ 48 mL

12. 16 mL 12 mL 21.63 36.5 mL

13. http://www.ptloma.edu/Physics/conversions.htm Use this site to make conversions from the English system to the Metric system. Interactive quizzes to see if you understand measuring distance volume temperature http://www.bbc.co.uk/skillswise/numbers/measuring/distance/quiz.shtml Choose level ‘A’ first, then proceed to level ‘B’ and ‘C’. http://www.bbc.co.uk/skillswise/numbers/measuring/lwc/quiz.shtml http://www.bbc.co.uk/skillswise/numbers/measuring/temperature/quiz.shtml

14. Finding volumes of regular objects and irregular objects. 75 – 50 = 25 mL

16. Burettes

17. Change in a burette 47 – 38 = 9 mL

18. ~ 39.24 mL The black/white card

19. Pipettes

20. Water in a pipette adheres to the side of the tube and forms a curved surface called a meniscus. By common practice, all readings are made at the bottom of the meniscus. The units for this pipette are milliliters (ml). 0.25 mL

21. At start of experiment 0.23 - 0.07 = 0.15 mL Ten minutes later:

22. Beakers with only one scale of numbers. ~ 159 mL 43 or 44 mL

23. Beakers with two scales of numbers. ~ 2050 mL

24. Mass • Kinds of balances • The standards • The way to read the scales

25. The same worldwide.

26. ~ 100.41 grams Mass MeasurementThe triple beam balance is commonly used to measure mass in the biology lab. T his device is named for its three long beams on which sliding bars called riders (or tares) are used to determine the mass of an object placed on its platform.    It is very important that the riders on the rear beams are in the notch for the whole number of grams and not in between notches. The front beam is a sliding scale graduated in grams. The rider on this beam can be positioned anywhere on the scale. Masses on a triple-beam balance can be read to tenths of a gram and estimated to hundredths of a gram.

27. The picture shows the measurement of a mass in progress.    Without estimation, the mass of the object appears to be 373.3 grams (g). ~ 373.3 grams

28. http://www.explorelearning.com/index.cfm?method=cResource.dspView&ResourceID=385 Practice measuring with this interactive site.

29. Length • Using a meter stick. • Converting metric units to other metric units. • Microscope ‘Field of View’. • Estimating size of microscopic organisms.

30. Problem:  How long is leaf A? The tip of the leaf is at about 6.5 cm, but note the measurement started at 1 cm.   Therefore, Leaf A is 5.5 cm or 55 mm. in length.

31. Converting metric units to other metric units.

32. Microscope ‘Field of View’.

34. View of a metric ruler Viewed under LOW power View of a metric ruler Viewed under MEDIUM power

36. The usefulness of measurement is enhanced by knowledge of its level of certainty.  Multiple measurements of the same property are like multiple shots at the same target.  The pattern of the shots tells you something about the measurement and its ability to describe the 'true' value of the property being sought.   The patterns depict possible outcomes of different experiments to measure the same property.  Expt IV is of course the best, because it give very reproducible results (precise) and also results that are very close to the true value or bull's-eye (accurate).  Experiment III is precise but not accurate.  It exhibits systematic error, which is very difficult to estimate at times. Accuracy and Precision http://www.brainpop.com/science/scientificinquriry/precisionandaccuracy/ A short video about this topic.