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Physics Toolkit Objectives
Use the metric system
Evaluate answers using dimensional analysis
Perform arithmetic operations using scientific notation
Distinguish between accuracy and precision
Determine the precision of measured quantities
Physics Toolkit What is Physics?
Physics is a branch of science that involves the study of the physical world: energy, matter, and how they are related
Physicists investigate the motions of electrons and rockets, the energy in sound waves and electrical circuits, the structure of a proton and of the universe
Physics uses mathematical equations for modeling observations and for making predictions
Physics Toolkit Fields in Physics
Acoustics AstronomyAstrophysicsAtomic PhysicsBiophysics ChaosChemical PhysicsComputational PhysicsCosmologyCryophysicsCrystallographyElectromagnetismElectronicsFluid Dynamics / Fluid MechanicsGeophysicsHigh Energy PhysicsHigh Pressure PhysicsLaser Physics
Mathematical PhysicsMechanicsWeather PhysicsMolecular Physics NanotechnologyNuclear PhysicsLight PhysicsParticle PhysicsPlasma PhysicsQuantum ElectrodynamicsQuantum Mechanics / Quantum PhysicsQuantum OpticsQuantum Field TheoryQuantum GravityRelativityStatistical MechanicsString Theory / Superstring TheoryThermodynamics
Physics Toolkit Solving Physics Problems
Step 1: Analyze the Problem
Rewrite the equation Substitute values
Step 2: Solve for the Unknown
Rewrite the equation so the unknown is alone on the left
Step 3: Evaluate the Answer
Physics Toolkit Solving Physics Problems
A light bulb with a resistance of 50.0 ohms is used in a circuit with a 9.0 volt battery. What is the current (amperes) through the bulb? (V = IR)
An object with uniform acceleration (a), starting from rest, will reach a velocity (v) in time (t) according to the formula v = at. What is the acceleration of a bicyclist who accelerates from rest to 7.00 m/s in 4.00 s?
The pressure on a surface is equal to the force divided by the area, P = F/A. A 53 kg woman exerts a force (weight) of 520 newtons (N). If the pressure exerted on the floor is 32,500 N/m2, what is the area of the soles of her shoes?
Physics Toolkit Standard Units
The Système International d’Unités, or SI, uses seven base quantities
Physics Toolkit Standard Units
Base quantities are defined in terms of direct measurements. Derived units created by combining base units
SI system is regulated by the International Bureau of Weights and Measures in Sèvres, France
National Institute of Science and Technology
(NIST) in Gaithersburg, Maryland, also
keeps standards of length, time, and mass
against which our meter sticks, clocks,
and balances are calibrated
Physics Toolkit Dimensional Analysis
You will often need to use different versions of a formula, or use a string of formulas, to solve a physics problem
To check that you have set up a problem correctly, write the equation or set of equations you plan to use with the appropriate units
Method of treating the units as algebraic quantities, which can be cancelled. Also used in choosing conversion factors
Dimensional Analysis
Conversion factor – multiplier equal to 1
Since 1 kg = 1000 g, it has these conversion factors
Choose conversion factor that makes units cancel, leaving answer in correct units
To convert 1.34 kg of iron ore to grams
Physics Toolkit
Physics Toolkit Dimensional Analysis
How many seconds are there in a leap year?
Covert the speed 5.300 m/s to km/hr.
Convert 5021 centimeters to kilometers.
Physics Toolkit Significant Digits
A pen is measured using a meter stick and recorded as 14.3 cm
Three valid digits: two you are sure of, and one estimated
Valid digits in measurement are significant digits
Last digit given is uncertain but significant
Physics Toolkit Significant Digits
All nonzero digits in a measurement are significant, but not all zeros are significant
Example: 0.0860 m. First two zeros only locate decimal point and are not significant
The last zero is estimated digit and significant
Physics Toolkit Significant Digits
When you perform any arithmetic operation, result can never be more precise than the least-precise measurement
To add or subtract measurements, first perform the operation, then round to correspond to the least-precise value involved
To multiply or divide, perform the calculation and then round to the same number of significant digits as the least-precise measurement
Note that significant digits are considered only when calculating with measurements
Physics Toolkit Scientific Models
Scientific model - idea, equation, structure, or system to model phenomenon explained
Based on experimentation
If the new data does not fit, then
both new data and model
re-examined
Physics Toolkit Scientific Law
Scientific law – rule of nature that sums up related observations to describe a pattern in nature
Physics Toolkit Scientific Theory
Scientific theory – explanation based on many observations supported by experimental results
Best available explanation of why things work as they do May serve as explanations for laws
In scientific use, only a very well-supported explanation is called a theory
Laws and theories may be revised or discarded over time
Physics Toolkit Measurement
Measurement – comparison between unknown quantity and standard
Quantify observations Enable you to derive relationship between any two quantities
Physics Toolkit Measurement Results
When a measurement is made, the results are often reported with uncertainty
Therefore, before fully accepting new data, other scientists examine the experiment, looking for possible sources of errors, and try to reproduce the results
A new measurement that is within the margin of uncertainty confirms the old measurement
Physics Toolkit Techniques of Measurement
To assure precision and accuracy, measuring instruments need to be used correctly
One common source of error comes from angle at which an instrument is read (parallax error)
Difference in readings caused by parallax, the apparent shift in position of an object when viewed from different angles