Chapter 1: Measurement And Physical Quantities Flashcards
1
Q
Qualitative descriptions
A
- Descriptions involving our senses
- Subjective, may vary depending on the observer
2
Q
Quantitative descriptions
A
- Descriptions involving measured quantities
- Each measured quantity consists of a number and unit
- Three most common fundamental quantities are: length, mass and time
3
Q
Physical quantities
A
- Measurable features are called physical quantities
- The international system of units called SI is commonly used around the world. Sometimes called the metric system
- Seven physical quantities and their fundamental units are: length (metre), mass (kg), time (s), electric current (ampere), temperature (kelvin), amount of substance (mole), luminous intensity (candela)
4
Q
Standard unit (base unit)
A
- A unit from which other units may be derived
- Standard unit of length is the metre (m)
- Standard unit of time is the second (s)
- Standard unit of mass is the kilogram (kg)
- Plus other four listed earlier
- All belong to a group called the fundamental quantities
5
Q
Derived quantities
A
- All units other than the seven fundamental quantities
- Called derived quantities because they can be stated in terms of the fundamental quantities
- You can have combinations of base units or have derived quantities that have been given specific names
- E.g. Metres per second, cubic metres, newton, coulomb, watt
6
Q
Metric prefixes
A
Pico - one million-millionth Nano - one thousand-millionth Micro - one millionth Milli - one thousandth Centi - one hundredth Deci - one tenth Kilo - one thousand Mega - one million Giga - one thousand million Tera - one million million
7
Q
Converting units: Two types
A
- From one SI unit to another SI unit (cm to m, km to m, hours to seconds)
- From a non-SI unit to an SI unit (pounds to kilograms, inches to cm)
8
Q
Scientific notation
A
- Alleviates the problem of extremely large and small numbers
- One numeral before the decimal point
- Leave numbers between 0.1 and 100 as they are (not in scientific notation)
9
Q
Significant figures
A
- Common in science to record all integers that are certain and one more in which there is some uncertainty
- The integers known with certainty plus the next figure are called significant figures
10
Q
Rules of significant figures
A
- All non-zero figures are significant
- All zeroes between non-zeroes are significant
- Zeroes to the right of a non-zero figure but to the left of the decimal point are not significant (109 000 has three sf)
- Zeroes to the right of a decimal point but to the left of a non-zero figure are not significant (0.050 has two sf)
- Zeroes to the right of a decimal point and following a non-zero are significant (104.50 has 5 sf)
11
Q
Order of magnitude
A
- Numerals greater than 3.16 become 10 and those below 3.16 become zero
12
Q
Measurements
A
- Unlike numbers, they can never be exact; all subject to error or uncertainty
- Errors can be introduced into an experiment when measurements are being taken
13
Q
Systematic error
A
- Results from a consistent problem with the measuring device (e.g. Zero error - pointer or end of ruler not on the zero mark to start with) or the person using it
- All readings are faulty in one direction
- Poor accuracy, definite causes, reproducible
- Minimised by calibrating the instrument, by adding or subtracting the known error, or by performing a more complex investigation
14
Q
Random error
A
- Results from variation in results about an average value
- Minimised by taking the average of several readings
- Poor precision, nonspecific causes, not reproducible
- Irregular errors of observation
- E.g. Parallax error
15
Q
Parallax error
A
- Results from changing your position when reading scales
- Overcome by viewing or reading the scale at a direct angle, or using a more precise instrument
16
Q
Mistakes
A
- Not errors in this context
- E.g. If you misread a scale by miscalculating the value of each division, it is called ‘scale reading error’ but is really just a mistake on your part
17
Q
Limit of reading
A
- The smallest division on an instrument is defined as its limit of reading
18
Q
Uncertainty
A
- The uncertainty associated with using an instrument is: ± half the limit of reading
- A measure of the limitations of the instrument
- e.g. For a ruler marked in mm, the absolute uncertainty is ± 0.5 mm
19
Q
Two ways uncertainty is expressed
A
Absolute uncertainty - the numerical value of half the limit of reading
Relative/Percentage uncertainty - a measure of how large the absolute uncertainty is when compared with the measurement itself
20
Q
Accuracy
A
- Accuracy of a measurement is determined by how closely an instrument’s measurement agrees with the true value for that measurement
- Difference is called the error
- The error is a measure of the accuracy of the result
- Absolute error = |observed value - accepted value| = |O - A|
- Relative error is the absolute error as a percentage of the accepted value
21
Q
Precision
A
- Precision of a measurement is an indication of its uncertainty and is determined by the relative uncertainty in the measurement and its number of significant digits
22
Q
Micrometer screw gauge
A
- Measures really tiny things, down to about one-hundredth of a millimetre
- Common micrometer has main scale marked off in half-millimetre divisions
- One revolution of thimble moves main shaft 0.5 mm
- Thimble divided into 50 divisions so that 1 mm equals 100 thimble scale divisions
- Hence 1 thimble scale division = 1/100 mm or 0.01 mm
23
Q
Vernier caliper
A
- Uses an auxiliary scale (the vernier scale) in conjunction with main scale to assist in estimating fractions of a main scale division
- Smallest possible division on the vernier scale is one-tenth of 1 mm (0.1 mm)
24
Q
Independent variable
A
- One controlled by the experimenter
- Placed along horizontal axis
25
Dependent variable
- Depends on the independent one
| - Placed along vertical axis
26
Linear relationships
- When two variables can be seen to be linear, we say they are directly proportional
- Form: y = mx + c
- Equation for slope: rise/run, or change in y/change in x
27
Interpolation
- The process of determining values of the dependent variable between the plotted points
28
Extrapolation
- The process of estimating values beyond measurements made in an experiment
29
Hyperbolic relationships
- One in which the dependent variable decreases as the independent variable increases
- Said to have an inverse relationship
- Variables said to be inversely proportional
30
Two main types of physics
Pure physics - involves research that increases scientific understanding of matter and energy; nature at the most fundamental level
Applied physics - uses knowledge of physics to develop many things helping to improve our lives
