Module 2 Foundations of Physics Flashcards
what are the seven SI units? what are the base units and what is the unit symbol for each one?
what are the prefix symbol and the factor for peta, tera, giga, mega, kilo, deci, centi, milli, micro, nano, pico, femto
answer these questions on si units and prefixes
what are the unit names, unit symbol and units expressed in SI units for;
Force, Pressure, Energy/work done, pwower, electric potential difference, electric charge, frequency
how do you convert degree celsius to kelvin?
add 273 e.g 20 degree celcius is 293 K
answer these questions on derived units
what is a systematic error?(imcluding zero errors)
what may they be caused by?
what do they affect?
- they are the same every time you repeat the experiment (they shift all values my the smae amount
- they may be caused by the equipment you’re using or how its set up e.g not lining the ruler correctly when meauring the extention of the spring
- thy affect the accuracy of your results
what is a random error? give examples, and how you can reduce random errors
- they’re what makes the results a bit different each time you repeat an experiment.
- e.g if you measured length of a wire 20 times the chances are youd get a slightly different value each time due to your head being in a slightly different position when reading the scale OR you cant keep the controlled varibles exactly the same in each experiment
- use more sensitive apparatus so that youre results can be more precise OR repeating the measurements
In a experiment how could you make your results more accurate?
- increase the number of your repeats which could help reduce the effect of the random errors in your results
- use the most appropriate equipment ( swapping millimetre ruler for a micrometer to measure the diameter of a wire) reducing the random error
- use a computer to collect data- using light gates to measure time interval rather than a stopwatch. makes results more precise by reducing human error.
what is the difference between precise, accurate and reliable results?
precise= the variation you see when you measure the same part repeatedly with the same device
accuracy= difference between the measurements and the part’s actual value
reliable= when you repeat your results or compare them to somebody else and see that you get the same result
what is the the absolute uncertainty?
how do you work out the absolute uncertainty?
-the total uncertainty for a measurement
absolute uncertainty= (max reading - min reading)/ 2
what is the percentage uncertainty?
how do you work out the percentage uncertainty?
- the uncertainty given as a percentage of the measurement
- you divide the absolute uncertainty by the known measurement and the multiply by 100
e. g (± 0.4/ 5) x 100= 8%
what is the smallest uncertainty you can have in a measurement?
± half of one division on the measuring instrument used
what is the rule when multiplying percentage uncertainties? e.g y=ab
you add the percentage uncertainties e.g
% uncern in y= % uncern in a + % uncern in b
what is the uncertainty on a mean of repeated results equal to?
half the range of the results
e.g 0.5 A, 0.3 A, 0.3 A, 0.3 A
range= 0.5 - 0.3
range= 0.2
absolute uncertainty of mean= ± 0.1
-what is the rule when dividing percentage uncertainties? e.g y=a/b
you add the percentage uncertainties e.g
% uncern in y= % uncern in a + % uncern in b
what is the rule when squaring or cubing percentage uncertainties?
e.g y=a2
you multiply the uncertainty
e.g % uncern in y= 2 x % uncern in a
how do you find the percentage difference?
-percentage difference= [first value- second value)/ (first value + second value)/2] x 100
what is a scalar quantity
a qauntity that has magnitude (size) but no direction
give examples of scalar quanities
- energy
- power
- mass
- voltage
- electric charge
- density
- work done
- denisty
- volume
- frequency
- electrical resistance
answer these questions on scalars and vectors
what is a vector quantity?
a quantity that has both magnitude and direction
give examples of vector quanities
weight
force
momentum
friction
field strength
where two vectors are parallel, you just add them together to fnd the resultant vector. the direction of the reultant is the same as the individual vectors but its magnitude is __________
where two vectors are antiparallel you call one direction positive (arrow head to the left) and the other negative (arrow head to the right), so you add the vectors to find the resultant.
where two vectors are parallel, you just add them together to fnd the resultant vector. the direction of the reultant is the same as the individual vectors but its magnitude is greater
resultant=- -3.0 + 4.0 = +1.0 (towards the right)
there are 2 methods of drawing perpendicular vectors
- Calculation: calculation using pythagoras theorem to find the magnitude of the resultant vector and trigonometry to find magnitude
- Scale Drawing: using sharp pencils, a long rule and protractor
answer these questions on parallel, antiparallel and perpendicular vectors
what are the two equations for the two components when resolving a vector
Fx=Fcos(angle)
Fy=Fsin(angle)
work out this question
answer this question
answer these questions
how do you add non perpendicular vectors?
- drawing by scale diagram: you will need to do this when both the magnitude and resultant are unkown. You can use a protractor to work out the angle in between the know forces (usually the opposite of the resultantforce you want to work out) and a ruler to measure the resultant force, mention the angle and which force it is relative to
- calculations using cosine and sine: the angle between the know forces is minus the given angle from 180 so then you can work out the resultant force using the cosine rule (a2 = b2 + c2 - 2bc cos(angle)). To find the angle you use the sine rule (a/sin A= b/sin B)
- vector resolution: for this method the diagram shown or you have drawn will be the same. you will be working out the vertidal and horizontal components. when working out the horizontal component you add the horizontal force to the diagonal force x cos(angle). once you have the forces for x and y you create another triangle putting x and y on the right sides. Then you work ou the resultant force by doing pythagoras theorem. to work out the magnitude you use tan-1.
Two forces of 5.0N and 3.0N act on a single point at 60 degrees to each other. What is the magnitude and the direction of the resultant force?
how do you subtract vectors?
answer these summary questions on adding non perpendicular vectors
answers
