Chapter 2 Equipment and Measurement

Transcription

1 27 Scientists often make measurements to quantify a certain phenomenon observed in the world around them measurements in the lab points to remember: room Let s say that Tariq s teacher has asked him to measure the length Tariq ofthe classroom How would he do it? There are a few important SCENTFC MEASUREMENT ALABAMA 8TH GiADE SCENCE STANDARDS COVERED N THS CHAPTER NCLUDE: Chapter 2 g used in this country Let s look at the units and equipment appropriate to a few common The United States has been a bit slow to comply, but metric units are now increasingly know the length ofthe room, but no one in Japan or Germany will understand the measurement, because the rest of the world uses the metric system All units must be common everywhere Tariq finally gets it room is 167 lengths of his feet? Great Now we have to measure Tanq s feet in order to denve the length of the together and tells us that the room measures 1 67 standard feet Well, now we All units must be common What if Tariq tells us that the length ofhis classroom and announces that it is 167, it doesn t mean much Yards, meters, feet? We need a unit All measurements must have a unit f Tariq measures the d Unités (S Units) Measuring dimension, volume and mass using Systëme nternational 1 dentify steps within the scientific process

2 J washing the car with a Brillo pad trying to paint your nails with a paint roller need the right tools fyou are in doubt about this, consider the following scenarios: it The measurements that you make are your data n order to make the measurements, you No matter how good your procedure is, it is not worth much ifyou cannot collect any data from THE RGHT TOOLS FOR THE RGHT JOBS 28 Let s say you wanted to compare bounces of a balance Figure 23 Triple-Beam Balance Now let s change our thinking a bit and consider how you could expand the bouncing ball investigation similarly sized balls that had different masses When change the tools you use To measure mass, you use you modify the experiment, you might also need to MASS linear (straight-line) distances Meter sticks measure distance in basic metric units called meters Sometimes you need a smaller tool than the meter stick Then you may use a ruler Rulers are Figure 22 Meter Stick 2 nches :jj1 :} n this investigation, you used a dropped and how high it Centimeters and inches are different kinds ofunits A centimeter is 1/1 of a meter; an inch is distance dimensions (length, width and height) ofan object One meter equals about three US units like the US Customary system (which is also known as English units) This makes it easier for scientists to compare data without converting the units Customary System feet S units are used by scientists all over the world, instead of regional 1/12 of a foot Meters are a unit defined by the nternational System (S) to measure the perfect tool for measuring usually marked in fractions ofmeters, called centimeters, and also in inches Figure 21 Meter Stick bounced A meter stick is the height from which the ball was # ;- meter stick to measure the LENGTH some tools will be unfamiliar to you at first So, we will start with three basic tools: the meter stick, the balance and the graduated cylinder your nails, wash the car or hammer in a nail You are learning the process of science now, and These are silly examples, but that is only because you know exactly what tool to use to paint using a can of soup to hammer in a nail ) E C Cu E > CCu z - D -J C? c1 C)

3 Chapter 2 Balances measure mass in units called grams They are different than grocery store scales, which measure in ounces and pounds (US Customary System units) Figure 23 shows a triplebeam balance, which is a great tool The analytical balance is even more accurate, and it has a digital display that tells you the mass to 4 decimal places VOLUME Now let s say we wanted to compare how much space is taken up by several types of balls Here, we are comparing their volumes We use a tool called a graduated cylinder to measure volume Liquid volume is measured in S units called liters The best way to measure volume using a graduated Figure24 GraduatedCylinder cylinder is to get at eye level with the numbers printed on its side Don t look at the cylinder from a position above or below the cylinder, because the volume will appear different than it actually is Looking directly at the cylinder, as in Figure 24, will allow you to read the volume ofthe liquid properly Sometimes the surface ofthe liquid will appear curved This is called the meniscus f the meniscus is curved upward like a smile, the volume is read from the lowest part ofthe curve This is the case with water and most other liquids, and is shown in Figure 24 fthe meniscus curves downward like a frown, the volume is read from the top of the curve So, the meter, gram and liter are the three base units ofthe S system Table 2 1 compares these units with their US Customary System counterparts F Co Co Co C? D - z Table 21 English-Metric Conversions English Metric Length 1 inches (in) = 254 cm 3281ft ;- im Mass O35oz ;-- ig 1 lb = 453 kg Volume 33Sfloz 1L igal 378L C Cu E C Cu C) E C, Challenge Activity Many products in your home list both the English and metric units Go on a scavenger hunt and collect one item from each room Describe the item you find and list both the English and metric units found on its label Kitchen Bathroom Family room Bed room Garage 29

4 which multiple of 1 point when making conversions from one unit to another system units are defined in multiples of 1 from the base unit The metric prefixes indicate The S system is also called the metric system This term is probably familiar to you Metric The table below is set up to help you know how far and in which direction to move a decimal 1, 1 or 1, the base unit should be multiplied or divided by CHANGNG THE MAGNTUDE factor of 1 Since 1 x 1 x 1 =1, you multiply by kg x 1 = 4,54 kg Here s another example A soda can has a volume of 355 milliliters (nil) To convert ml to Let s say you have a bowling ball with a mass of454 kilograms (kg) To convert kg to grams Some abbreviations, like the deciliter (dl), may be unfamiliar to you n the science lab, and in encounter However, all these units are correct, and some of the lesser-known ones are even in agriculture and forestry most real-life applications, kilo-, centi- and milli- will be the abbreviations that you most often deciliters (dl), you move two spaces to the left Since 1 x 1 = 1, you divide by 1, which common in particular industries The hectometer (hm), for instance, is a commonly used unit 355mL lo=355mlxo1=355dl is the same as multiplying by 1 (g), move three spaces to the right on the table Each ofthose spaces represents a multiplication Multiply when changing from a larger unit to a smaller one Divide when changing from a smaller unit to a larger one (Remember, dividing is the same as multiplying by a fraction) Let s look at two examples base unit) factor (from the kg hg dag gram dg cg mg Abbreviation ice hl dal Liter dl cl nil Multiplication km hm dam meter dm cm mm Prefix (k) (h) (da) kilo hecto deka deci centi milli Base Unit (U) (c) (m) Table 22 Changing the Magnitude of a Unit

5 Chapter 2! < E Activity The best way to get used to changing the magnitude ofthe units is to practice doing so Use the problems below to help you begin practicing,l 42 kg x = g 2 33 cm m 3 86 ml L mg g 5 11 hm x m mm km 7 32 L x ml 8 76 kg x mg 9 67 dl x ml 1 44 mm cm iii km g kg g x mg cm x = mm mm = cm 16 2 dl = L hm = km hm x = m m = km 2 2 L x = cl 21 1 kg x cg kg x = g g kg km x = m 25 7 m = km L x = 27 9 ml = L dm = mg = cg zzz 31

6 1 B size C volume B height A mass 1 Kilograms are a unit ofmeasurement for CHAPTER 2 REVEW 32 2 inches 345 : > :; a) B 2 in or 55 cm A 3Oinor59cm C 25inor62crn B 28mor7Ocm Centimeters 5 dentify the most accurate length of the leaf in the figure below B milliliters C millimeters A grams 4 Graduated cylinders are marked in units of B meters B to make it easier to understand and compare published results C to make it easier for scientists to misrepresent their results B to simplify the laws of physics system? A to simplify international patent laws 3 Why do scientists from countries around the world use the same measurement B 42g=4,2kg C 42g=42kg B 42g=O42kg A 42g=O42kg 2 dentify the correct conversion of42 grams (g) to kilograms (kg)