SPH 3U1

 “SI” stands for “Systeme International d’Unites”. It is a system of units used in measurement.  All physical quantities can be expressed as some combination of fundamental units, called base units QuantityQuantity Symbol UnitUnit Symbol LengthLMetreM MassMKilogramkg TimeTSeconds Electric Charge QCoulombC

 Units may be expressed with prefixes, e.g. 2.1 gigabytes or 2.1GB  Each prefix is associated with a power of 10 factor  To convert a measurement to base units, look up the correct factor and multiply  E.g. Convert 2.1 GB to B

 The most common method used to convert units is to multiply by conversion factors.  E.g. Convert 12km into miles (1 mile = 1.61km)

 Accuracy (or certainty)  Precision How close value is to accepted value How exact and reproducible a value is

Good accuracy, poor precision Good precision, poor accuracy Good accuracy, good precision

 All digits except leading zeros are significant m vs m  Counted numbers and defined values have an infinite number of significant digits 4 cars 24 hours = 1 day

 Round “down” when... The digit dropped is less than 5, 50, 500 etc., the remaining digit is left unchanged.  Round “up” when... Digit dropped is greater than or equal to 5, 50, 500 etc., the remaining digit is increased.  E.g. Round to three significant figures: seconds = meters = kilometers =

 State final answer with the same number of decimal places as the number with the least number of decimal places. E.g. 251 cm cm =

 State final answer with the same number of significant digits as the number with the least number of significant digits.  E.g m ÷ 2.23 s =

 Calculate: 50 m x 121 m = 2.10 cm ÷ s = How can we express each of the above to the correct number of significant digits?

Number from 1 to <10, expressed to correct significant digits Power of 10 multiplier Unit 4.19 x m/s

 Move the decimal left or right to express the number as a value between 1 and <10.  Round the number to the correct number of significant digits.  Count the number of spaces the decimal place has been moved. This indicates the value of the exponent. IF MOVED TO THE RIGHT, the exponent is NEGATIVE IF MOVED TO THE LEFT, the exponent is POSITIVE

 Express m 3 to three figures.  Express m/s to two figures.

 Every measurement has some degree of uncertainty in the last (right most) digit. What is the length of the rod using Ruler A? Which digits are you certain of? Which are you uncertain of? How could you express this uncertainty in your measurement? What about Ruler B?

 Error in measurements may also be expressed as a percentage Percent error or relative error:  Percent difference Indicates difference between two or more measurements