Physics is the science, which addresses the interaction between matter and energy. Physics is the science, which attempts to explain all of the fundamental truths of the observable universe. The preferred language of physics is mathematics. A physicist attempts to explain and as much as possible predict physical phenomena by incorporating quantitative information into mathematical relationships called equations. So you should develop your quantitative skills to the fullest extent of your abilities.
Arguably, all of science can be considered branches of physics, however we will be kind to biologists, chemists, meteorologists, and others and let them think that they are pursuing separate academic disciplines.
The ultimate goal of physics is to find and develop an explanation of the entire universe and hopefully express it as an equation that will fit on a T-shirt.
Measurement is the process by which people express quantitatively to each other aspects of the observable universe. In order to engage in the process of measurement a common standard of measure must be used. Ancient measurement systems used objects or parts of the human body for standards.
The metric system (i.e., System International) is used by the scientific community for the measurement of physical quantity.
The metric system uses seven fundamental units (see the chart below) to measure all aspects of the physical world.
All of the fundamental units are conceptual units (units based on repeatable physical phenomena such as the wavelength of light etc.) except mass. Mass is still based on a standard kilogram mass kept in the International Bureau of Weights and Measures in France.
|Physical Quantity||Symbol Used In Equations||Unit Of Measure||Unit Symbol|
|amount of substance||(none)||mole||mol|
Fundamental units can be combined to form derived units. For example: speed is the rate at which a moving body
covers ground. The derived unit used for speed therefore is the meter per second (m/s). This unit is a combination of the fundamental units for length of distance (meters) and for elapsed time (seconds).
Units in the metric system are modified by prefixes which indicate the order of magnitude of the base unit. An example is centi which stands for 1/100 of the base unit. One centimeter represents 1/100 of a meter.
Significant digits in an experimental measurement are all the numbers that can be read directly from the instrument scale (known with certainty) plus one estimated (doubtful) number.
|All non-zero digits are significant.||1.345 Kg has 4 significant digits|
|All zeros between non-zero digits are significant||220005 Km has 6 significant digits|
|Zeros to the right of a non-zero digit but to the left of an understood decimal are not significant.||230000 g has 2 significant digits|
|Zeros to the right of the decimal but to the left of a non-zero digit are not significant||0.0000345 m has 3 significant digits|
|Zeros to the right of the decimal following a non-zero digit are significant.||0.10070 cm has 5 significant digits|
The closeness of a result to its accepted value is the accuracy of the result. That which detrimentally affects accuracy is called error. There are three sources of experimental error.
Human error sometimes called personal error arises from personal bias or carelessness in reading an instrument, in recording data, or in calculations.
Systematic error is associated with equipment problems such as an improperly
zeroed instrument or an incorrectly calibrated device.
Random error results from unknown and unpredicted variations in experimental conditions. Random errors are often beyond the control of the experimenter. Voltage spikes, vibrations, and temperature fluctuations are all examples of the causes of random error.
Absolute error (Ea) is the numerical difference between the accepted value for a result and the actual experimental value. Equation: Ea = Experimental value - Accepted value.
Relative error (Er) is a more meaningful representation of error in an experimental setting. The relative error represents the fractional error. You may have called this fractional error percent error. Equation: Er = (Ea/Accepted) (100%). (But both absolute and relative error presume you have a way to know the true or accepted value. Often this is unavailable to scientists until measurements have been performed many times using a variety of procedures.)
Mean or average can be computed for a set of data by using this equation: Xmean = ( X1 + X2 + X3 ... XN ) / N where X1 , X2 , etc. are the data points. N is the number of data points in the data set.Percent difference is a simple way to show agreement among data.
Absolute deviation represents the absolute value of the difference between a data point and the mean of the data. Equation: δa = X - mean.
Mean absolute deviation represents the mean or average of the absolute deviations of a set of data. When reporting the result of an experiment, the result may be expressed as: Mean of the data ± mean absolute deviation. Example: 123 ± 2 cm.
Relative deviation represents the fractional deviation for a set of data. To find the relative deviation use the following equation: ( mean absolute deviation / mean of the data ) (100%). When reporting the result of an experiment, the result may be expressed as: Mean of the data ± relative deviation. Example: 123 cm ± 0.5%.
It is often convenient to represent experimental data in graphical form for the purposes of reporting and obtaining information (such as slopes).
Quantities are commonly plotted on Cartesian graph grids in which the horizontal (X) is called the abscissa and the vertical (Y) is called the ordinate.
When two quantities are directly related the graph yields a straight line. These quantities are considered to have a linear relationship. The general equation is (Y = mX + b)
The slope of the line is useful in many physics applications. The slope is found by dividing the Rise (Y) by the Run (X). The unit used for the slope is determined by the X and Y units. Example: X represents time (s) and Y represents distance (m), this would yield a slope which has the unit m/s.
If one quantity increases proportionally as the other decreases, an inverse relationship is present. The graph of an inverses relationship is a hyperbola. The general equation is (X)(Y) = k.
If one quantity increases as the square of the other then a quadratic relationship is present. The resulting graph is a parabola. The general equation is Y = kX2.
|TRIAL||DATA (UNITS)||δa (UNITS)|
|MASS (Kg)||WEIGHT (N)|
|VOL. (cm3)||MASS (g)|
|MASS (Kg)||ACCEL. (m/s2)|
|FORCE (N)||ACCEL. (m/s2)|
William Dietsch edited & posted 1 April 2007 by D Trapp