Regent Physics PowerPoint Presentation. Physics Units. I. Physics Skills II. Mechanics III. Energy IV. Electricity and Magnetism V. Waves VI. Modern Physics. I. Physics Skills. A. Scientific Notation B. Graphing C. Significant Figures D. Units E. Prefixes F. Estimation.
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Physics Units • I. Physics Skills • II. Mechanics • III. Energy • IV. Electricity and Magnetism • V. Waves • VI. Modern Physics
I. Physics Skills • A. Scientific Notation • B. Graphing • C. Significant Figures • D. Units • E. Prefixes • F. Estimation
A. Scientific Notation • Use for very large or very small numbers • Write number with one digit to the left of the decimal followed by an exponent (1.5 x 105) • Examples: 2.1 x 103 represents 2100 and 3.6 x 10-4 represents 0.00036
Scientific Notation Problems • 1. Write 365,000,000 in scientific notation • 2. Write 0.000087 in scientific notation
Answers • 1.) 3.65 x 108 • 2.) 8.7 x 10-5
B. Graphing • Use graphs to make a “picture” of scientific data • “independent variable”, the one you change in your experiment is graphed on the “x” axis and listed first in a table • “dependent variable”, the one changed by your experiment is graphed on the “y” axis and listed second in a table
Best fit “line” or “curve” is drawn once points are plotted. Does not have to go through all points. Just gives you the “trend” of the points • The “slope” of the line is given as the change in the “y” value divided by the change in the “x” value
Types of Graphs • 1. Direct Relationship means an increase/decrease in one variable causes an increase/decrease in the other • Example below
2. Inverse(indirect) relationship means that an increase in one variable causes a decrease in the other variable and vice versa • Examples
3. Constant proportion means that a change in one variable doesn’t affect the other variable Example;
4. If either variable is squared(whether the relationship is direct or indirect), the graph will curve more steeply.
C. Significant figures • Uncertainty in measurements is expressed by using significant figures • The more accurate or precise a measurement is, the more digits will be significant
Significant Figure Rules • 1. Zeros that appear before a nonzero digit are not significant (examples: 0.002 has 1 significant figure and 0.13 has 2 significant figures) • 2. Zeros that appear between nonzero digits are significant (examples: 1002 has 4 significant figures and 0.405 has 3 significant figures)
Significant figures rules(cont.) • 3. zeros that appear after a nonzero digit are significant only if they are followed by a decimal point (20. has 2 sig figs) or if they appear to the right of the decimal point (35.0 has 3 sig figs)
Sig Fig problems • 1. How many significant figures does 0.050900 contain? • 2. How many significant figures does 4800 contain?
Answers • 1. 5 sig figs • 2. 2 sig figs
D. Units • 1. Fundamental units are units that can’t be broken down • 2. Derived units are made up of other units and then renamed • 3. SI units are standardized units used by scientists worldwide
Fundamental Units • Meter (m)– length, distance, displacement, height, radius, elongation or compression of a spring, amplitude, wavelength • Kilogram (kg)– mass • Second (s)– time, period • Ampere (A)– electric current • Degree (o)– angle
Derived Units • Meter per second (m/s)– speed, velocity • Meter per second squared (m/s2)– acceleration • Newton (N)– force • Kilogram times meter per second (kg.m/s)– momentum • Newton times second (N.s)-- impulse
Derived Units (cont.) • Joule (J)– work, all types of energy • Watt (W)– power • Coulomb (C)– electric charge • Newton per Coulomb (N/C)– electric field strength (intensity) • Volt (V)- potential difference (voltage) • Electronvolt (eV)– energy (small amounts)
Derived Units (cont.) • Ohm (Ω)– resistance • Ohm times meter (Ω.m)– resistivity • Weber (Wb)– number of magnetic field (flux) lines • Tesla (T)– magnetic field (flux) density • Hertz (Hz)-- frequency
E. Prefixes • Adding prefixes to base units makes them smaller or larger by powers of ten • The prefixes used in Regents Physics are tera, giga, mega, kilo, deci, centi, milli, micro, nano and pico
Prefix Examples • A terameter is 1012 meters, so… 4 Tm would be 4 000 000 000 000 meters • A gigagram is 109 grams, so… 9 Gg would be 9 000 000 000 grams • A megawatt is 106 watts, so… 100 MW would be 100 000 000 watts • A kilometer is 103 meters, so… 45 km would be 45 000 meters
Prefix examples (cont.) • A decigram is 10-1 gram, so… 15 dg would be 1.5 grams • A centiwatt is 10-2 watt, so… 2 dW would be 0.02 Watt • A millisecond is 10-3 second, so… 42 ms would be 0.042 second
Prefix examples (cont.) • A microvolt is 10-6 volt, so… 8 µV would be 0.000 008 volt • A nanojoule is 10-9 joule, so… 530 nJ would be 0.000 000 530 joule • A picometer is 10-12 meter, so… 677 pm would be 0.000 000 000 677 meter
Prefix Problems • 1.) 16 terameters would be how many meters? • 2.) 2500 milligrams would be how many grams? • 3.) 1596 volts would be how many gigavolts? • 4.) 687 amperes would be how many nanoamperes?
Answers • 1.) 16 000 000 000 000 meters • 2.) 2.500 grams • 3.) 1596 000 000 000 gigavolts • 4.) 0.000 000 687 amperes
F. Estimation • You can estimate an answer to a problem by rounding the known information • You also should have an idea of how large common units are
Estimation (cont.) • 2 cans of Progresso soup are just about the mass of 1 kilogram • 1 medium apple weighs 1 newton • The length of an average Physics student’s leg is 1 meter
Estimation Problems • 1.) Which object weighs approximately one newton? Dime, paper clip, student, golf ball • 2.) How high is an average doorknob from the floor? 101m, 100m, 101m, 10-2m
Answers • 1.) golf ball • 2.) 100m
II. Mechanics • A. Kinematics; vectors, velocity, acceleration • B. Kinematics; freefall • C. Statics • D. Dynamics • E. 2-dimensional motion • F. Uniform Circular motion • G. Mass, Weight, Gravity • H. Friction • I. Momentum and Impulse
Kinematics; vectors, velocity, acceleration • In physics, quantities can be vector or scalar • VECTOR quantities have a magnitude (a number), a unit and a direction • Example; 22m(south)
SCALAR quantities only have a magnitude and a unit • Example; 22m
VECTOR quantities; displacement, velocity, acceleration, force, weight, momentum, impulse, electric field strength • SCALAR quantities; distance, mass, time, speed, work(energy), power
Distance vs. Displacement • Distance is the entire pathway an object travels • Displacement is the “shortest” pathway from the beginning to the end
Distance/Displacement Problems • 1.) A student walks 12m due north and then 5m due east. What is the student’s resultant displacement? Distance? • 2.) A student walks 50m due north and then walks 30m due south. What is the student’s resultant displacement? Distance?
Answers • 1.) 13m (NE) for displacement 17 m for distance • 2.) 20m (N) for displacement 80 m for distance
Speed vs. Velocity • Speed is the distance an object moves in a unit of time • Velocity is the displacement of an object in a unit of time
Speed/Velocity Problems • 1.) A boy is coasting down a hill on a skateboard. At 1.0s he is traveling at 4.0m/s and at 4.0s he is traveling at 10.0m/s. What distance did he travel during that time period? (In all problems given in Regents Physics, assume acceleration is constant)
Answers • 1.) You must first find the boy’s average speed/velocity before you are able to find the distance
Acceleration • The time rate change of velocity is acceleration (how much you speed up or slow down in a unit of time) • We will only be dealing with constant (uniform) acceleration
Constant Acceleration Problems • 1.) A car initially travels at 20m/s on a straight, horizontal road. The driver applies the brakes, causing the car to slow down at a constant rate of 2m/s2 until it comes to a stop. What was the car’s stopping distance? (Use two different methods to solve the problem)
Answers • First Method vi=20m/s vf=0m/s a=2m/s2 Use vf2=vi2+2ad to find “d” d=100m