hi everyone welcome back to this channel this is timothy from cognito academy and this video we will be learning measurements more specifically physical quantities and units let's first start off with the concept of physical quantity physical quantity like the mass of an object is the quantity of the object that we can measure a physical quantity is represented by a magnitude and a unit like 10 kilograms where 10 is the magnitude and kilogram is the unit there are two types of physical quantities quantities and derived quantities let's first touch on the base quantities first which are fundamental physical quantities that are not defined in terms of other quantities in layman terms they are the most basic quantities like these seven types of base quantities and the five base quantities that you need to know are length mass time temperature and current you also need to know their respective si unit associated to them namely meters for length kilograms for mass second for time kelvin for temperature and ampere for current say we are measuring a very small fraction of time of 0.0001 seconds but instead of repeating so many zeros we can bring in standard form and write it in terms of 10 to the power of negative 6 to simplify this expression and in terms of naming we name this 10 to the power of negative 6 as micro meaning that we can call this a microsecond this micro term is called a prefix which comes before the unit and this is how we simplify the naming of very small or large quantities by using prefixes which come before the unit here's a list of prefixes and their respective standard form that you need to memorize going from smallers from nano micro melee centi to desi to the prefixes they are above one kilo mega and giga we have touched on base quantities which are the most basic quantities like length the other classification of physical quantity is derived quantities that's derived by combining various base quantities for example volume is derived quantity which is made by multiplying three measurements of length namely the length breadth and height and our derived quantity is speed which is distance divided by time so as we can see these derived quantities are derived by combining various base quantities now we come to the concept of precision which is the smallest unit an instrument can measure like for a normal meter rule which can measure up to the smallest division of a millimeter used for measuring lengths between several centimeters up to a meter an instrument with a higher precision than this ruler will be the burner caliper able to measure lengths to a precision of 0.1 millimeter and is best suited for measuring lengths between 1 and 15 centimeters for even smaller lengths we use the micrometer screw gauge which measures small lengths to an astonishing precision of 0.01 millimeters and is best suited for measuring small lengths below 2.5 centimeters to measure time we can use a stopwatch a typical stopwatch might have a precision of up to three decimal places of a second but we will only take readings to the nearest one decimal place which for this case 30.9 second this is to negate the random error introduced due to humor reaction time here we have a pendulum and a period is defined as the time taken for one complete cycle for the pendulum to make one full back and fourth swing to find the duration of one such period we will record the duration for 20 periods then divide this measured time by 20 to get a duration of a period by doing so we reduce the inaccuracy due to humor reaction time by a factor of 20. another way to increase accuracy of our readings is to take multiple timings for our 20 periods and then take the average duration for this 20 periods before dividing by 20. a coma experimental error is parallax error which occurs when the measurement deviates from the true measurement due to your eye being positioned at an angle to the measurement markings to prevent parallax error place your eye directly at the level of the appropriate measurement marking when measuring say the length of a woolen plank or the level of a liquid in a graduated cylinder this wraps up our video on measurements if you liked this video and found it helpful do like and subscribe and turn on the notification bell to stay tuned for more content see you