M OTION AKA: Physics W HAT IS PHYSICS ? VIDEO I S T HIS M OTION ? If you want to understand how an object (like a car, ball, person, or rocket) moves, you have to understand three things about what it means "to be moving." These three things are: Position. This is precisely where an object is located. Speed. Precisely how fast an object is moving. Acceleration. Precisely how fast an object's speed is changing. P RECISION & M EASUREMENT 'Precision' refers to 'the number of significant digits' or the 'number of decimal places' you use when recording the result. Even if the person making a measurement is as accurate as humanly possible, limitations imposed by the measuring instrument, variations in dimensions of the object being measured, and the conditions under which the measurement is being made, dictate that the result should not imply greater precision than circumstances warrant. T IPS KNOW THIS! All digits included in a stated value, with the exception of leading zeros, are significant. Ignore the decimal point when counting sig figs. How many sig figs? 1.25 cm mph m/s 0.57 km m cm 60 mm WHEN ALL ELSE FAILS look to YODA! P RECISION R ULE FOR A DDING & S UBTRACTING The answer of an addition or a subtraction should be rounded off to the least precise value involved. (the measurement with the fewest decimal places). e.g cm cm cm ( math answer ) cm (answer has only one decimal place because cm has only 1 decimal place and is the least precise) R OUNDING If the digit after the one you want to keep is 5 or greater, then round up m rounded to 2 significant digits is 3.5 m. If the digit after the one you want keep is less than 5, then round down m rounded to 2 significant digits is 3.4 m. T HE C ERTAINTY R ULE FOR M ULTIPLYING & D IVIDING If youre multiplying two 4 digit numbers your answer will produce a seven or eight digit answer. How do we know how many significant digits to include? Follow this rule: When multiplying and/or dividing, the answer has the same number of significant digits as the measurement with the fewest number of significant digits. D ISTANCE & T IME Distance is the amount of space between two objects or points. The most common unit of measurement is the metre. The most common units of distance (length) and their relationships are: km = kilometre m = metre cm = centimetre mm = millimetre 1 km = 1000 m 1 m = 100 cm 1 cm = 10 mm T IME Time is the duration between two events, and is usually measured in seconds, minutes, or hours. The units of time and their relationships are: d = day h = hour min = minute s = second 1 day = 24 h 1 h = 60 min 1 min = 60 s Y OUR T URN Work on the Measurement and Sig Figs Sheets for homework.