Scientific Method Scientific Method

Making Observations Observations lead to questions Questions lead to answers

Hypothesis A hypothesis is a proposed explanation for an observation. You must be able to test a hypothesis. If experimental data does not fit a hypothesis you may need to change your hypothesis.

Experiments Experiments are used to test hypotheses. Anything that can change in an experiment is called a variable. ◦ The variable that you change during the experiment is called the independent variable, or the manipulated variable. ◦ The variable that is observed during the experiment is called the dependant variable, or responding variable. ◦ Other factors that can change in an experiment must be kept constant or controlled so that you can relate the dependant variable to the independent variable.

Theories A theory is a well tested explanation for a broad set of observations. Theories are not static and may need to be changed in the future to due new observations of experimental results.

Scientific Laws A law is a concise statement that summarizes the results of many observations and experiments. Laws do not try to explain why something happens. That would require a theory.

Scientific Notation Scientific notation takes the form: M x 10 n M is some number between 1 and 9 n represents the number of decimal places to be moved ◦ A positive n indicates that the number is large ◦ A negative n indicates that the number is between 0 and 1

Converting to Scientific Notation Move the decimal so that there is one number between 1-9 in front of the decimal. ◦ If there is no decimal, it is located after the last 0 at the right side of the number. ◦ If you move the decimal to the left the exponent is positive and if you move the decimal to the right the exponent is negative. Example 1: = Example 2: =

Convert the following to scientific notation = = = = Convert the following to standard notation 8.23 x 10 3 = 7.12 x = 3.67 x 10 8 = x =

Significant Figures Measured quantities are always reported in a way that shows the precision of the measurement. ◦ Precision is the degree of exactness of a measurement, how many decimal places an instrument can measure. Significant figures are digits in a measurement that are known with certainty. Accuracy is the extent at which a measurement approaches the true value.

Degree of Precision

Draw darts to show the following Good accuracy and good precision Good accuracy and poor precision Poor accuracy and good precision Poor accuracy and poor precision

Significant Figures If the decimal is present start from the left side and start counting digits when you see a number from If the decimal is absent start form the right side and start counting digits when you see a number from Example 1: = Example 2: = Pacific Side Decimal is present Atlantic Side Decimal is absent

Write the number of significant figures = x 10 4 = = 0.1 x =

Calculations using significant figures Calculations using significant figures When multiplying or dividing, round to the least number of significant figures in any of the factors. Example: 23.0cm x 432 cm x 19cm = 190,000cm 3 When adding or subtracting, round your answer to the least number of decimal places in any of the numbers that makes up your answer. Example: ml ml ml = 255.5ml

Perform the following calculations expressing the answer in the correct number of significant figures m x1.2 m = 3.5 cm x 2.50 cm x cm = cm 3  3.2 cm = m/s m/s = 150 ml – 23.5 ml =

Experimental Error Error = |experimental value – accepted value| Experimental error is usually expressed as a percentage. Percent error = |error| x 100 Accepted value

Experimental Error A technician experimentally determined the boiling point of octane to be ºC. The actual bp of octane is ºC. Calculate the error and percent error.

All SI units are derived from 7 basic units QuantityUnitAbbreviation Length Mass Time Temperature Electric Charge Amount of Substance Luminous Intensity

International System of Units Based on metric system Common units and quantities ◦ Length ◦ Volume ◦ Mass ◦ Temperature ◦ Energy

Conversions Move the decimal point to the left or right to convert within the metric system. ◦ If you are going from a smaller unit to a larger unit move the decimal to the left. ◦ If you are going from a larger unit to a smaller unit move the decimal to the right. kilohectodeca Base Unit (1) decicentimilli khdaMeter (m)dcm Gram (g) Liter (l)

Convert the following measurements 245 m = _____________ cm 305 kg = _____________ g 35 mm = ______________ m 1250 cm = _____________ m 358 ml = ______________ l 2350 g = ______________kg 35 dm = ______________m 67 hm = ______________m

In order to convert between different units of measurement you need to use conversion factors and the factor-label method. Example: A football field is 100. yds long. How long is that in m? 100. yards = 91.7 m 1.09 yd 1 m

Example: A horse can gallop at a speed of 42.0 mph. How fast can the horse gallop in m/s? h 42.0 mi = 18.8 m/s 3600 s 1 h 1 mi 1609 m

Convert the following English Standard Units to Metric Units. If I were to hit a home run down the left side of Jacobs Field the ball would have to travel at least 325 ft. How far is that in m? The top speed of a human is 10.4 m/s. How fast is that in mph?

A race car can travel around 225 mph. How fast is that in m/s? A person can walk about 3.1 mph. How fast is that in m/s?

Density Density = mass/volume Is density an extensive or intensive property. Density generally increases with temperature. ◦ Does anyone know an exception to this rule?