Physics Vocabulary

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The Law of Conservation of Energy

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States that energy can change form, but is never lost.

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Science

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consists of the laws that are the general truths of nature and the body of knowledge they encompass.

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Physics

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the most basic of the sciences concerning itself with the interactions of energy, matter, space, and time, and especially with questions of what underlies every phenomenon.

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Laws of Nature

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are concise descriptions of the universe around us; they are human statements of the underlying rules or laws that all natural processes follow.

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Model

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is a mental image or analogy to ojects or phenomena that we can experimence directly. EX planetary model of the atom in which electrons are pictured as orbiting the nucleus, analogous to the way planets orbit the sun.

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Theory

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is usually a larger-scale and more broadly applicable generalization than a model and often seeks to describe nature with mathematical precision.

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Law

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is reserved for a concise and very general statement, such as the law that energy is conserved in any process, or Newton's second law of motion, which relates force, mass, and acceleration via the simple equation F=ma.

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Principle

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less broadly applicable statements . EX Pascal's principle: only applicable in fluids

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The models, theories, and laws we devise sometimes imply:

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sometimes imply the existence of objects or phenomena as yet unobserved. EX: The law of conservation of energy implied the existence of particles called neutrinos years before they were actually observed.

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If experiment does not verify our predictions:

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then the theory or law is wrong, no matter how dear it is.

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Einstein's famous equation precisely states the connection between mass and energy.

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E=mc2

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Physics greek origins

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greek, meaning nature. The study of nature came to be called Natural Philosophy.

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Classical Physics

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Physics as it developed from the Renaissance to the end of the 19th century. Not an exact description of the universe.

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Classical Physics is an excellent approximation under the following conditions:

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matter must be moving at speeds less than about 1% the speed of light. The objects dealt with must be large enough to be seen with a microscope, and only weak gravitational fields, such as on earth, can be involved.

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Modern Physics

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consists of the two revolutionary theories, relativity and quantum mechanics. These deal with the fast and the small, respectively.

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Relativity

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must be used whenever an object is traveling at greater than about 1% of the speed of light or experiences a strong gravitational field such as that near the sun.

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Quantum Mechanics

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must be used for objects smaller than can be seen with a microscope.

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Relativistic Quantum Mechanics

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combination of Relativity and Quantum Mechanics, and must be used when small objects travel at high speeds or experience a strong gravitational field. Best universally applicable theory.

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Goal of Physics:

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to describe the physical universe- both to gather knowledge about it and to discover the physical laws that rule it.

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Defining a Physical Quantity

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defined by either specifying how it is measured or by stating how it is calculated from other measurements.

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Operational Definition

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defines something in terms of a specific process or explicitly to some component.

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Unit

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numerical measurements relative to some standard.

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SI Units

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French: system international

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Fundamental Units

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a set of units for physical quantities from which every other unit can be gathered.

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Derived Units

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a unit that is defined by a simple combination of base units. EX length, mass, time, and charge. EX speed = length/time

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Second

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abv: s

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Meter

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abv: m

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Time

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abv: s

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Charge

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abv: C

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Kilograms

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abv: kg

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Speed of light

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abv: c

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Metric System

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factors of 10 are used to span the ranges of values

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Accuracy

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is how close a measurement is to the "true" value- and no measurement is exact.

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Uncertainty

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in a measurement is an estimate of the amount it can be off from the "true" value.

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Conversion Factor

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means by which to change something to a different version or form.

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δ

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the symbol for uncertainty EX 9.5 seconds can be anywhere from 9.0 to 10 because of an uncertainty (δ) of 0.5 ; therefore, t ± δt = (9.5 ±0.5)

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In experimental work scientists need only to describe nature within experimental uncertainties in order to be valid

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In experimental work scientists need only to describe nature within experimental uncertainties in order to be valid

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Factors contributing to uncertainty in a measurement include

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1. limitations of the measuring devise 2. the skill of the person making the measurement 3. irregularities in the object being measured 4. any other factors that affect the outcome (highly dependent on the situation)

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Percent Uncertainty

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the uncertainty measurement of a value expressed as a percentage or a simply ratio. EX (9.5 ±0.5) = 0.05s/9.5s * 100 = 0.5% &&& %unc= δA/A * 100

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Method of Adding Percents

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the percent uncertainty in a quantity calculated by multiplication or division is the sum of the percent uncertainties in the items used to make the calculation.

EX L= 4.0m ; W=3.0m ; unc 2%&1%' ; the the area of the floor is 12.0m(squared) and has an uncertainty of 3%. Expressed as an area this is 0.36m(squared) , which we round to 0.4m(squared) since the percent is a single digit.

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Method of Significant Figures

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the rule is that the last digit written down is the first digit with some uncertainty. The number of the digits is then the number of significant figures.
EX 9.84 ± 0.05 = 3 significant figures

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Zeros

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Zeros are significant except when they serve only as place keepers.
EX 0.053 - 2 sigfigs
10.053- 5 sigfigs
1300 - 1, 3, 5, sigfigs. best to right in scientific notation so that we can be sure that they are not place keepers.

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SigFigs in Calculators RULES of multiplication and division

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1. multiplication and division. Here the rule is that the result has the same number of sigfigs as the quantity having the least sigfigs entering the calculation. EX A= π r(squared) = (3.1415927..)(1.2msquared) = 4.5238934m(squared) >> should be A=4.5m(squared)

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SigFigs in Calculators RULES of addition and subtraction

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The last sigfig in addition and subtraction is in the same column as the last sigfig in the least accurate number. EX: 7.56 =accurate to .01 ; -6.052= accurate to 0.001 ; 13.7 = accurate to 0.1 ; 7.56+-6.052+13.7= 15.208 , but correct is 15.2 because least accurate would be 13.7 and most accurate would be -6.052.