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Physics Chapter 1: Measurements - Coggle Diagram
Physics Chapter 1: Measurements
physical quantity
quantity that consists of a numerical magnitude and a unit and it can be measured
electric current
measured in ampere(A)
measured by ammeter
temperature
measured in kelvin(K), other measurements include degree Celsius(C)
measured by a mercury thermometer ranging from -10degC to 110degC, digital thermometer ranging to 42degC
time
measured in seconds(s), other measurements include minutes(min) and hours(h)
measured by digital stopwatch which has an accuracy of 0.01 seconds and analogue stopwatches, precision of up to 0.1 seconds
amt of substance
measured in molecule(mol)
mass
measured in kilograms(kg), other measurements include grams(g) and tonnes(t)
measured by electronic balance or electronic weighing scale, precision of 0.1kg
length
Measured in metres(m), other measurements include centimetre(cm) and kilometres(km)
measured by a measuring tape, zero to a few metres precision of 0.1 cm, metre rule, zero to one metre precision of 0.1cm, vernier calipers measure the depth of an object, and the diameter of an object, zero to 15 cm, precision of 0.01cm
other measurements
area, length x breadth, m2, volume, length x length x length, m3, speed, distance over time, m/s
precision rules
addition and subtraction, final answers to be in 2sf, workings can be more, try to be in 4-5sf
multiplication and division, final answers to be in 2sf, workings can be more, try 4-5sf
in general, do not use ratios, fractions, or roots in final answers, only use decimals and/or digits, coordinates read from a graph must be precise of half the smallest square, use exact or 5sf (if need to) values from previous calculations for subsequent calculations
prefixes
help to simplify big numbers, e.g. 10^12 tera, 10^9 giga, 10^6 mega, 10^3 kilo, 10^-1 deci, 10^-2 centi, 10^-3 milli
avoid errors when reading
parallax error
align eyes so the line of sight is perpendicular to the markings on the measuring tool
pendulum swings
every complete left to right swing is one oscillation
the period of a pendulum is the time taken for one complete oscillation
to calculate period, step 1: time 20 oscillations. step 2: repeat the time for the 20 oscillations. step 3 calculate average time by taking the time taken for the first 20 oscillations and add the time taken for the next 20 oscillations and divide them by 2. step 4: take the average time taken and divide by 20
DEPENDENT ON LENGTH OF PENDULUM
digital stopwatches have an accuracy of 0.1s, this is to take into account human reaction time which is abt 0.3-0.5s
to avoid human reaction time, take the readings several times and take the average or increase the total time taken so the percentage error is smaller
scalar quantities
scalar quantities include distance, speed, mass, energy and time
vector quantities
vector quantities include displacement, velocity, weight, force and accleration
there are parallel vectors and non-parallel vectors
non-parallel vectors act on the same object but in different directions
parallel vectors arevectors acting on the same object and in a single straight line and they can be added or subtracted
vector polygon
used for addition of >2 vectors, use sin rule from math, used when angle and opposite vector is known
subtraction of vectors, can be seen as adding a negative vector eg. A-B -> A+(-B)
other errors
systematic errors
results in all readings/measurements being always below/above the true value by a fixed amount, can be eliminated only if source of error is known and accounted for, CANNOT BE ELIMINATED BY REPEATING measurements and averaging them, e.g. not accounting zero error in a measurement, or not accounting for background radiation when measuring the activity of a radioactive source
random errors
results in readings or measurements being scattered about a mean value, have an equal chance in being positive/negative, CAN BE REDUCED by repeating a measurement and averaging, plotting a graph and drawing a best fit line for the plotted points, eg. fluctuation in count of a radioactive decay and variation in the diameter of a piece of wire
forces in equilibrium
polygon of forces, when MORE THAN 3 forces in the same plane are in equilibrium, they form a closed polygon when represented in a vector diagram using the head-to-tail method
triangle of forces, when 3 forces in the same plane acting on a point are in equilibrium, they form a closed triangle when represented in a vector diagram, using the head-to-tail method
