Scientific Method, Units of Measurement, Scientific Notation, Significant Figures BASICS OF PHYSICAL SCIENCE

Transcription

1 Scientific Method, Units of Measurement, Scientific Notation, Significant Figures BASICS OF PHYSICAL SCIENCE

2 EQ: WHAT IS PHYSICAL SCIENCE? The sciences can be divided into 2 main branches: and Natural science is divided into earth, life and physical sciences Physical science covers non-living things These areas include and Chemistry is the study of matter and its properties Physics is the study of matter and energy and interactions between forces and motion

3 PHYSICAL SCIENCE We use the scientific method to answer questions scientifically The scientific method consists of the following steps:

4 Matter Throughout the course, we ll focus on. Matter is anything that has 2 major properties: and. Anything that has mass and takes up space is matter. This means that almost everything is matter except things like light, sound, thoughts, feelings and ideas.

5 Properties of Matter are the characteristics we use to describe matter. Properties can be or. Chemical properties are those characteristics that can only be detected with a chemical reaction like ph, reactivity and flammability. Physical properties are those that can be easily observed like color, shape, texture, odor and density. We re going to use density to demonstrate some basic information that you need to know.

6 Density is how much matter is in a volume of a substance. Density tells us if an object will float or sink. Light objects (with less matter) float. Heavy objects (with more matter) sink. Examples of light objects: Examples of heavy objects:

7 Float or Sink? Will these items float or sink? A golf ball? A ping pong ball? Why? Even though they are about the same size, the golf ball is heavier and therefore has a greater mass:volume ratio. Can of Coke? Can of Diet Coke? Why the difference? The Diet Coke does not have the sugar that the regular Coke does and so it is less dense and therefore floats.

8 Density Calculations Density = mass/volume D = m/v Units: g/cm 3 or g/ml MASS DENSITY x VOLUME NOTE: (A cubic centimeter is the same as a milliliter.) You can use the triangle to find any unknown as long as you have two of the items. Just cover the item that you re looking for and you will have the formula to calculate it.

9 Density Calculations A piece of tin has a mass of g and a volume of 2.26 cm 3. What is the density of tin? Density = mass/volume Mass = g Volume = 2.26 cm 3 Density = g/ 2.26 cm 3 Density = 7.31 g/cm 3 Questions?

10 PHYSICAL SCIENCE In order to communicate your findings to others, you must use a common language Parts of this language include: Used to write very large or very small numbers in a shorter way Numbers without units don t mean a thing! When measuring items there are only so many digits that actually mean something.

11 EQ: HOW DO YOU EXPRESS NUMBERS IN SCIENTIFIC NOTATION? Move the decimal after the first number (NOT A ZERO!); round off to 2 decimal places Your first number should be between 1 & 9! Keep track of the number of places you moved the decimal The number of decimal places will become the exponent for the 10 If you moved the decimal right, the exponent is negative; if you moved the decimal left, the exponent is positive Example: 123,456,789 Example: More Practice! Even More Practice!

12 EQ: HOW DO I ENTER NUMBERS IN SCIENTIFIC NOTATION INTO MY CALCULATOR? Find your key w/ee Key in the decimal Press whatever it takes to get the EE on your screen (could be EE or 2 nd EE) Key in the exponent DO NOT KEY IN THE x10 part it will throw your entire calculation off.

13 SCIENTIFIC NOTATION When performing calculations with numbers in scientific notation: Multiplication: Multiply the numbers, then, add the exponents Example: (1.1 x 10 3 )(2.4 x 10 3 ) = Division: Divide the numbers, then subtract the exponents (numerator denominator) Example: (2.6 x 10 6 )/(1.1 x 10 3 )= More Practice Even More Practice!

14 EQ: HOW DO WE DETERMINE WHICH UNITS TO USE FOR VARIOUS MEASUREMENTS? Scientists use the International System of Units or the SI units The SI units are based on the metric system Every type of measurement has a base unit Length: meter (m) Mass: kilogram (kg) Temperature: kelvin (K) Time: second (s) Units are VERY IMPORTANT! Numbers without units are meaningless!

15 METRIC PREFIXES To accommodate very small measurements or very large measurements, we can add prefixes to the base unit A metric prefix tell us how many times a unit should be multiplied or divided by 10 Common metric prefixes: (1,000 or 1 x 10 3 ) (100 or 1 x 10 2 ) (10 or 1 x 10 1 ) (0.1 or 1 x10-1 ) (0.01 or 1 x 10-2 ) (0.001 or 1 x 10-3 )

16 EQ: HOW DO I CONVERT UNITS WITH PREFIXES? Technically, you have to divide or multiply by the unit of ten, but there is an easier way. King Henry Died By Drinking Chocolate Milk The first letter of each word in the sentence above stands for the common metric prefixes K = kilo H = hecta D = deka B = BASE D = deci C = centi M = milli

17 CONVERTING BETWEEN METRIC PREFIXES To convert from one to another, simply count the number of places you have to move to get from one to the other Move your decimal the same number of places and in the same direction. Example: Convert kilometers to millimeters K H D B d c m

18 EQ: WHAT ARE SIGNIFICANT FIGURES AND WHAT IS THEIR IMPORTANCE? When we use measurements in calculations, our answer can t be anymore precise than the original calculations Precision is a measure of how exact a measurement is.more numbers Take the value of pi for example: Pi = Pi = 3.14 When looking at this, the first value is more precise than the second.

19 SIGNIFICANT FIGURES Scientist use to determine how a measurement is. Significant digits in a measurement include all of the plus one.

20 FOR EXAMPLE Look at the ruler below What would be the measurement in the correct number of sig figs?

21 THE SAME RULES APPLY WITH ALL INSTRUMENTS The same rules apply Read to the last digit that you know Estimate the final digit

22 LET S TRY GRADUATED CYLINDERS Look at the graduated cylinder below What would be the measurement in the correct number of sig figs?

23 RULES FOR SIGNIFICANT FIGURES RULE #1 All non zero digits are ALWAYS significant How many significant digits are in the following numbers?

24 RULE #2 All zeros between significant digits are ALWAYS significant How many significant digits are in the following numbers?

25 RULE #3 All FINAL zeros to the right of the decimal ARE significant How many significant digits are in the following numbers?

26 RULE #4 All zeros that act as place holders are NOT significant Another way to say this is: zeros are only significant if they are between significant digits OR are the very final thing at the end of a decimal

27 FOR EXAMPLE How many significant digits are in the following numbers? 1) ) 6.02 x ) ) ) 800 1) 2) 3) 4) 5)

28 RULE #5 All counting numbers and constants have an infinite number of significant digits For example: 1 hour = 60 minutes 12 inches = 1 foot 24 hours = 1 day There are 30 students in the class

29 HOW MANY SIGNIFICANT DIGITS ARE IN THE FOLLOWING NUMBERS? 1) ) ) ) 7.90 x ) ) ) ) 2) 3) 4) 5) 6) 7)

30 SIGNIFICANT FIGURES If you have two calculations that you re using, your answer can t have more numbers than your original measurements If I multiply 2.3 and 3.1, I end up with This answer is not valid because it has 2 decimal places when my original measurements only had 1. This is where significant figures come into play

31 SIGNIFICANT FIGURES Significant figures are all the digits that are known in a measurement When counting significant figures, every digit 1-9 counts Zeros are the funny ones! Zeros are only significant in two situations: When between two other significant figures When it is the last number after the decimal

32 SIGNIFICANT FIGURES Let s Practice!

33 CALCULATIONS WITH SIGNIFICANT FIGURES When adding or subtracting, the final answer can have no more significant figures after the decimal than the one with the least amount g H 2 O g salt g solution You can only have one number after the decimal because the mass of water only has one

34 CALCULATIONS WITH SIGNIFICANT FIGURES When multiplying or dividing, you can have no more total significant figures in your answer than you have in your measurement that contains the least amount. The total number of sig. figs. count here not only those behind the decimal! If you were to multiply 1.23 by 4.5, you could only have 2 significant figures in your answer What if you multiplied 67.8 by 9?

35 ROUNDING OFF If you have too many significant figures, you must round off to the correct amount The same rounding rules apply Look at the number behind the rounding number 5 or more, round up; 4 or less, leave it the same.