2 Foundations Of Physics Flashcards
Independent variable
The variable for which value is changed or selected by the investigator
Dependent variable
The variable of which the value is measured for each and every change in independent variable
Control variable
A variable which, in addition to the IV, affects the outcome of the investigation so has to be kept constant or monitored
Interval
Quantity between readings
Reproducible
If the investigation is repeated by another person or by using different equipment or techniques and the same results are obtained
Repeatable
If the original experimenter repeats the investigation using the same method and equipment and obtains the same results
Hypothesis
A proposal intended to explain certain facts or observations
Resolution
The greater the resolution of the measuring instrument is, the smaller the smallest increment that can be measured to e.g. a metre ruler marked off in mm has greater resolution than one marked in cm
Error
The difference between the measured value and the true value of the thing being measured
Uncertainty
A quantification of the doubt about the measured result
Random error
Humans and the equipment have limitations
Systematic error
that does not happen by chance but instead is introduced by an inaccuracy in the apparatus or its use by the person conducting the investigation.
o Zero Error: an error that occurs when the apparatus shows a non-zero value when it should be registering a value of exactly zero.
o Parallax Error: an error produced whenever a scale, gauge, or pointer is observed wrongly during scientific experimentation due to position of viewing and perception.
SI meaning
International system of units
The six SI base units
Length- m Mass- kg Time- s Electric current- A Temp- k Amount of substance- mol
What’s a derived unit
A unit that can be worked out from the base units
Prefixes
Peta Tera Giga Mega Kilo Deci Centi Milli Micro Nano Pico Femto
Peta
10^15
Tera
10^12
Giga
10^9
Mega
10^6
Kilo
10^3
Deci
10^-1
Centi
10^-2
Milli
10^-3
Micro
10^-6
Nano
10^-9
Pico
10^-12
Femto
10^-15
Homogeneity of physical equations
It is said that an equation is homogenous if both sides of the equations can be simplified to the same base unit or set of base units. This means that the equation could be correct, as long as there are no numerical errors made.
If an equation is not homogenous then it is incorrect.
Accuracy
An experiment is accurate if the quantity being measured has a value that’s very close to the commonly accepted or true value.
Precision
The results of an experiment are precise if they are close together and have a small range. The smaller the range of the repeated values, the higher the precision. The term precision is linked to the spread of the data or the percentage uncertainty in a measurement. A precise experiment has a smaller spread in the data or the smaller the uncertainty.
Single readings uncertainty
If single readings have been taken then the uncertainty should be the smallest interval or division on the measuring instrument. Consider the example below.
o Example: A metre rule is used to measure the length of a book. uncertainty in the measuring instrument (the ruler) = ± 1mm length = (295 ± 1) mm
Percentage uncertainty
Percentage Uncertainty = (Uncertainty/Average value ) x 100
o Referring back to the previous example about the ruler, The percentage uncertainty in
the length is % uncertainty = ± (1/295) x 100 = ±0.34%
Multiple readings uncertainty
If multiple readings have been taken then half of the range of the readings will be the uncertainty in the measured or calculated quantity.
Readings versus measurements
Readings:
No zero error
Uncertainty is half resolution
Examples: measuring cylinder, weighing scales, thermometer
Measurements:
Zero error
Uncertainty is resolution
Examples: ruler, protractor, stopwatch
Adding or subtracting uncertainties rule
Add absolute uncertainties
Multiplying or dividing uncertainties rule
Add percentage uncertainties
Raising an uncertainty to a power rule
Multiply percentage uncertainties by the power
How to determine the uncertainty in a gradient
a. Error bars may be added to each plotted point if the data points are not too scattered.
b. Draw a best fit line through the scattered points (or through the error bars). The worst acceptable line is then drawn. This will either be the steepest or shallowest line.
c. Determine the gradient of the best fit line and the gradient of the worst acceptable line.
d. Uncertainty = |gradient of best fit line – gradient of worst acceptable line|.
e. The percentage uncertainty in the gradient can be determined as follows:
Percentage Uncertainty = (Uncertainty/Gradient of best fit line) x 100
Working out error bars
If each stage in iv is repeated for several results, squad all results
Find range of repeats
When drawing- half uncertainty
What is a scalar quantity
quantity which only has magnitude
What is a vector quantity
quantity that has both magnitude and direction.
Scalar quantity examples
Mass Time Temperature Length Speed Energy
Vector quantity examples
Displacement Force Velocity Acceleration Momentum
How to remember base SI units
Kelvin Kills Small Angry Mole Men
True value=
Observed value + error
Observed value=
True value + random error + systematic error
