. OBJECTIVES The purpose of this lab is to familiarize the student with techniques of measurement and also with the concept of density. B. BACKGROUND Density is defined as MASS divided by VOLUME. Volume can be measured as liquid volume (liters, pints, quarts) or as cubic linear volume (I x w x ht, cm3, in3). If a geometric object has regular dimensions, there may be a formula for calculating the volume (rectangular solid is length x width x height; cylinder is pr2 x height). The mass is determined by weighing. In the metric system, mass is expressed in grams (or kilograms). Once mass and volume are determined, density is calculated directly from the formula D = M / V. C. EQUIPMENT You will need a ruler marked in centimeters, a kitchen scale for weighing in grams, 2 blocks of wood that are different sizes but made of the same type of wood, and a brick. If you have a scale that only measures in ounces and pounds, you can convert to grams. Take the weight in pounds, divide by 2.2, and then multiply by 1,000. If you have a friendly grocer, you may be able to weigh your wood blocks on the scale in the vegetable section. D. PROCEDURES 1. Determine the mass of the first wood block to the nearest gram. If your scale is metric, read the mass directly in grams. Otherwise, convert ounces to pounds, pounds to kilograms, and kilograms to grams. (Example: You weigh the block to be 5 oz. To change ounces to pounds, divide by 16 oz. in a pound. So your measurement of 5 oz. divided by 16 oz/lb equals 0.31 pounds. Next, divide 0.31 by 2.2 and get .1409 kilograms. Finally, multiply .1409 by 1,000 to get 140.9 g. Your measurement to the nearest gram is 141 g.) 2. Measure dimensions of the block in centimeters: Length ____________ Width ____________ Height ____________ Calculate the volume from the formula: V = 1 x w x h Volume cm3
Calculate density by dividing volume into mass: Density g/cm3
Repeat measurements and calculations for the second wood block. The density of pure water is 1.0 g/cm3. If an object has a density lower than water, it will float. From your calculations, predict whether the blocks will float. Now put them in a pan of water and verify your answer. If the two blocks were made of the same material, they should have the same density no matter what sizes they are. Are your calculations for density the same for both blocks? If not, consider some sources of error in your measurements. Calculate the density of a brick or other heavy rectangular solid. Should it float? It is possible to determine the volume of objects that are irregular. Instead of measuring dimensions, the object is immersed in water in a container that has accurate markings for liquid volume on its walls. This could be done with a glass measuring cup or a graduated cylinder (from a chemistry laboratory). Fill the measuring cup to the halfway mark. Carefully lower an object into the water, being careful not to splash. After the water surface is calm, read the new water level. The increase in water volume is the volume of the immersed object. This method is only accurate if you have an accurately marked cup or cylinder. OPTIONAL: DETERMINE THE DENSITY OF A SPARK PLUG OR OTHER IRREGULAR OBJECT.
RESULTS AND CONCLUSIONS Record all your calculations neatly for your lab report. Answer any questions that were raised in the above discussion. Try to think of some practical applications to using density. Could density be a useful measurement for identifying different metals or other substances? Solve this problem: Archimedes had to protect the king from being swindled. If the king’s new crown had a mass of 2790 g, and he knew the density of gold to be 15g/cm3, how much water must the crown displace when submerged if the crown is pure gold?
laboratory report should contain the following sections: (1) Hypothesis, (2) Procedures,
(3) Observations and Results, and (4) Conclusions. Make certain you include all four headings with at least a short paragraph for each. In addition, tables, graphs, and answers to questions may be necessary in the latter two sections.
Scientific research should contain a preliminary statement of the expected outcome of the experiment. This can include predictions of the specific experiment or the general anticipated result. If you are merely doing an observation and have no idea of the outcome, you cannot make an actual hypothesis. Instead, make a short statement of the purpose of the observation. However, if you have preconceived ideas of the outcome, include them in this section, and then see how they compare to the results.
Even though you are told what to do, write a paragraph of the specific steps you actually took in doing the experiment or observation. Because you are coming up with your own equipment, your procedures will be of particular interest.
OBSERVATIONS AND RESULTS
This is where you should make a detailed statement of the outcome of your experiment. Record all your pertinent observations in a clear, readable form. Arrange your data in tables (such as measurements and calculations you make). Answer any questions asked in this Study Guide, marking these clearly so that they can be easily found.
Your conclusions should include a comparison between the outcome of the experiment and your initial predictions made in the hypothesis. In cases where you are attempting to recreate a physical constant, compare your number to the accepted value, using the formula for experimental error:
Experimental Error Equation
If you find a large difference in your results from the expected value or if your anticipated observations are not the same as your actual observations, try to identify possible sources of error or reasons for the difference in the hypothesis and results