Chapter 2 Measurement

Description and Measurement 2.1

A. Measurement A way to describe the world with numbers Answers questions such as how much, how long, or how far Can describe cost ($), distance, volume, mass, speed In scientific endeavors, scientists rely on measurements instead of opinions Why is it important for doctors to know how much the heart pumps blood?

When would it be important to measure an amount of air? Air available inside of an airplane Air inside of a firefighter’s airpac Air inside of a rocket ship for astronauts

Why is it important for certain events, like swimming to be measured? Events can be measured Why is it important for certain events, like swimming to be measured? 2008 Summer Olympics, Michael Phelps swam the 100m butterfly and won his 7th gold medal for a singles event by a hundredth of a second Michael Phelps – 50.57 Milorad Cavic – 50.58

B. Estimation To give a rough measurement of an object Usually used when you don’t have the right tool to make an exact measurement Can use your knowledge of the size of something familiar to estimate the size of a new object A skill based on previous experience and is useful when you are in a hurry and exact numbers are not required A valuable skill that improves with experience, practice, and understanding

When do you estimate? Come up with one on your own. How much bread a restaurant warms up for the different tables coming in. How many papers to print off for a meeting. How much money you need for a trip. How much ingredients to put in a recipe. How much dog food to put in the bowl.

c. 1. Precision One way to evaluate measurements is to determine whether they are precise Precise – a description of how close measurements are to each other Precision is used when discussing the number of decimal places a measuring device can measure A wall clock or a clock with a second hand Making a measurement and getting the same result each time or your friend measuring the same thing and getting different answers each time

c. 2. Accuracy When you compare a measurement to the real, actual, or accepted value The second hand on a watch will give a precise time (7:38:10 p.m.) but it’s not accurate if it is 25 minutes behind “But officer, my speedometer says I’m only going 40?!”

c.3. Rounding a measurement Not all measurements require an exact measurement Rounding rules Look at the number to the right of the place you are rounding If it is 0-4, it stays the same If it is 5-9, it goes up one The length of the walk to school. You could measure it to nearest millimeter But only would need to know to the nearest meter or tenth of a meter and still be accurate such as 2,348.50

c. 4. precision and number of digits Let’s say you have a bag of M&M’s and you want to share it with your friends. There are 4 of you and 30 M&M’s… Each of you will get 7 M&M’s but there are 2 left over? Would you bother to cut the 2 M&M’s in half so everyone gets exactly the same amount or would someone just eat the 2 extra M&M’s?

c.5. Using precision and Significant digits Significant digits or figures – the number of digits that truly reflect the precision of a number Digits other than zero are always significant Final zeros after a decimal point (6.54600 g) are significant Zeros between any other digits (507.0301 g) are significant Zeros before any other digits (0.0002030 g) are NOT significant Zeros in a whole number (1650) may or may not be significant An exact number, such as the number of people in a room or the number of meters in a kilometer, has infinite significant digits

C.6. Following the rules Multiplication and division, you determine the number of significant digits in each number in your problem 6.14 x 5.6 = 34 .384 3 digits 2 digits 2 digits For addition and subtraction, you determine the place value of each number in your problem 6.14 to the hundredths + 5.6 to the tenths 11.7 4 to the tenths

2.2 SI Units

A. The international system It would be awfully confusing if every country in the world had a different system of measurement. In 1960, scientists established the International System of Units (SI) as the accepted system for measurement Designed for a worldwide standard of physical measurement for science, industry and commerce

Si base units

b. length The distance between two points Depending on the tool depends on what you are measuring and depending on what you are measuring depends on what you are measuring! Meter – the SI unit of length one meter is about the length of a baseball bat 1 meter = 3.28084 feet Size of a room or a building would be measured in meters

Smaller objects can be measured in centimeters (cm) or millimeters (mm) Textbook or pencil could be measured in cm Twenty dollar bill is 15.5 cm long Mm could be used to measure the letters in your text book Scientist use micrometers and nanometers to measure really small things such as blood cells, bacteria or viruses

b.1. a long way Long distances are measured with kilometers such as distance from the earth to the moon or how long a bird flies Kilometers are also used for distance in a car or length of a long race OBJECT TYPE OF MEASUREMENT MEASUREMENT Can of soda Volume 355 cm to 3rd power Bag of potatoes Mass 4.5 kg Fluorescent tube Length 1.2 m Refrigerator Temperature 276 K

c. volume the amount of space an object occupies You can measure smaller volumes with cubic centimeters To find the volume of an object, measure its length, width, and height and multiply them

Liter – a measurement of liquid volume Ex. a 2-L water bottle

c.1. volume by immersion To find the volume of something that is irregularly shaped, you can simply add it to water If you add ice cubes to a full glass of water, the water that spills over is displaced due to the addition of the volume of ice The volume of the water was not increased, but the volume of the ice displaced the water The difference in the volume of the ice cubes that are under the surface of the water Ice cubes took up space and caused the total volume in the glass to increase

Add the irregular shaped item to a glass of water, but you must start with knowing the volume of the water first The increase of volume of water is equal to the volume of the object

d. mass Mass – the amount of matter in an object Kilogram – (kg) SI unit for mass One liter of water has a mass of 1 kg Smaller masses are measured in grams (g) One gram is the size of a large paper clip A triple beam balance can determine mass

Weight and mass are not the same. Mass depends only on the amount of matter in an object Mass won’t change when only your location changes Elevators and space shuttles

d.1. weight Measurement of force SI unit is newton (N) Depends on gravity which can change depending on where the object is located Spring scale is used to measure how a planet’s gravitational force pulls on objects

Your weight would be different on other planets This is because of the gravitational force difference on each planet If you weigh 75 pounds on Earth, which is 332 N, on Mars you would be 126 N and 782 on Jupiter

e. temperature Physical property of temperature is related to how hot or cold an object is A measure of kinetic energy, or energy of motion, of the particles that make up matter Fahrenheit and Celsius are the most common forms of temperature scales Thermometer is a tool used to measure temps Kelvin (K) is the SI unit for temperature

f. Time and rates Time is an interval between two events SI unit of time is second (s) Hour (h) is not an SI unit but it is used for long periods of time Rate – the amount of change of one measurement in a given amount of time Speed is the most familiar rate in which the SI unit is kilometers per hour (km/h) You don’t have to use km/h to measure speed but you can use measurement of an object during an event such as how many cars pass through an intersection per hour (cars/hour)

Drawings, tables, and graphs 2.3

a. Scientific illustrations A.1. Drawings Sometimes best choice to show details Drawing can emphasize only the things that are necessary to show If something tends to be the same color, the drawing can depict the different layers

A drawing can also show something difficult to see such as the solar system or the whole Earth

Quick sketches help to model problems Such as drawing the outline of two continents and finding if they fit together

Drawing can show hidden things such as the water cycle or what the inside of a building looks like or where muscles in your arm are

a.2. PHotographs Still photographs shows an object exactly as it is at a single moment in time Movies show how an object moves and can be slowed down or sped up to show interesting features

b. Tables and graphs