Post on 16-Jan-2016
MEASUREMENTS
How exact? How many fingers?How accurate? What do you weigh?How precise? Are you tall?
ApproximationEstimationUncertainty
Orders of magnitude
MEASUREMENTS
SPACE - LENGTH, AREA, VOLUME
MASS
TIME
TEMPERATURE
Actually Temp. is a property of Mass and velocity (dist/time)
UNITS OF MEASUREMENT
Length: Babylonian inch= 25 barleycornsFoot = length of a foot, 12 inchesYard = Henry V’s nose to index fingerCubit = forearm, 18 inchesHand = width of palm, 4 inches?Furlong = 40 rods, 220 yds, 10 chainsChain = 22 yardsRod/Pole/Perch = 1/4 chain = 5 1/2 ydsMile (statute) = 8 furlongs, 5280 feetLeague = 3 land milesMile (naut) = 6076.11 feetFathom = 6 feetCable = 12 fathoms
UNITS OF MEASUREMENT
RADIAL
Arc-second “minute = 60 arc-sec ‘degree = 60 minutes o
full circle = 360 degrees
UNITS OF MEASUREMENT
AREA: Acre = one day’s ploughing= 1 furlong x 1 chain= 220 x 22 yards= 4840 square yards
square rod = 30 1/4 sq ydsarpentsquare footsquare yard = 3 x3 = 9 square feetsquare mile = 640 acres
UNITS OF MEASUREMENT
VOLUME ounce=3 tbsp, 9 tspcup = 8 oz, 16 tbsppeck = 8 qts (dry)bushel= 2150.42 cu.in. = 4 pecks
= one man-load= 56 lbs
teaspoontablespoon = 3 tsp,
= 1/3 ozgill, drampinch, dash < 1/8 tsp
cubic inchcubic foot= 1728 cu incubic yard=27 cu ftpint = 2 cups, 16 ozquart = 2 ptsgallon = 4 qtsgal (US)=231 cu.in.barrel(US)= 31 1/2 galcord = 128 cu.ft.
UNITS OF MEASUREMENT
MASS: OunceTroy ouncepound = 16 ozslug ton = 2000 or 2200 lbshundredweight (cwt)
DENSITY
DENSITY = MASS per unit VOLUME
Principle of buoyancy
Hieron’s challenge to Archimedes in 250 BC
Density of gold = 19.3 gm/cc, Cu= 8.92 gm/cc
UNITS OF MEASUREMENT
TIME blink, flash, twinkling, etc. as quick as you can say Jack Robinsonsecondminute = 60 secondshour = 60 minutesday = 24 hoursweek = 7 daysmonth= 28-31 days, Lunar month = one lunar cycle = 28 daysYear = 12 months, ~13 lunar monthsDecade = 10 yearsCentury = 10 decades, 100 yrsMillenium= 10 centuries, 1000 yrseon, era, age, lifetime, coon’s age
UNITS OF MEASUREMENT
TEMPERATURE
Degree (fahrenheit)
F
C
K
32o
0o
273.16
212o
100o
373.16
~100o
37o
H2O freezes Body Temperature. H 2O boils
0o
-17o
UNITS OF MEASUREMENT
THE METRIC SYSTEM: SI
LENGTH MASS TIME TEMPERATURE
METRE KILOGRAM SECOND KELVINcentimetre gram degree Celsius
METRIC MEASURES
Metre: 1/40,000,000 of thecircumference of the earth on a longitude line through Paris
Second: 1/84600 mean solar day
Kilogram: a lump of platinum in Paris
Metre: 1,650,763.73 wavelengths of Kr 86 emission
or: the distance light travels in a vacuum in 299,792,458 seconds
Second: 9,192,631,770 oscillations of Cs
A BIT MORE PRECISION
4-DIMENSIONSup/down; across; backwards/forwards
and time
IMAGINE A “THREE”
DIMENSIONALWORLD
FLATLAND!
THE NOTION OF MOTION
DISTANCE
VELOCITY: DISTANCE PER UNIT TIME
ACCELERATION: CHANGE IN VELOCITY WITH TIME
FORCE = MASS X ACCELERATION
AN EXPERIMENT IN MOTION
APPARATUS
EXPERIMENT
REPORT
Car, odometer, watch, paper, pencil, driver, observer/recorder
Record the odometer reading every minute, on the minute, during a ride through the city, of at least 30 minutes duration.
Plot a graph of distance vs time
Galileo and Gravity
Galileo’s observations on gravity
It is not “natural” that all things come to a stop
NEWTON’S THREE LAWS
1. Inertia LawA body stays motionless or in motion ina straight line unless acted upon by a force.
2. Force = mass x acceleration
3. For every action there is an equal and opposite reaction
MOMENTUM
• MOMENTUM IS THE PRODUCT OF MASS AND VELOCITY
• M=m x v or M = md/t
• IN ANY SYSTEM MOMENTUM IS CONSERVED
Force of gravity F = GMm/d2
GRAVITY BY NEWTON
F = Gmm’/d2 where m and m’ are known masses
G = Fd2/mm’ = gravitational constant=6.67 x 10-11 m3/kg-s2
M = Fd2/Gm = mass of the earth= 6 x 10 24 kg
Known: m, d, F (= mg) Unknown: M (Mass of earth)
TORSION PENDULUM
m
m M
M
mirrorscreen
F = GMm/d2
d
Centre of Gravity
FOR EVERY OBJECT THERE IS A POINT WHICH CAN BE TREATED AS THE POINT ON WHICH AND FROM WHICH THE FORCE OF GRAVITY CAN BE ASSUMED TO ACT.
This point need not be within the object.
FORCES
CONTACT FORCES
ACTION-AT-A-DISTANCE FORCES
Frictional forcetensional forcenormal forceair resistance forceapplied forcespring force
Gravitational forceelectrical forcemagnetic force
WORK
Work is the product of force over a distance
W = F x d = mad
HOW HARD, HOW FAR YOU PUSHHOW HIGH, HOW HEAVY YOU LIFT
UNIT: JOULE = NEWTON-METRE
Did Sisyphus do any work?
POWER
Power is the rate of doing work or the rate of using energy
P = Fd/t = mad/t
UNIT: WATT = NEWTON-METRE/SECOND
MACHINES EMPOWER MAN
By extending the application of force over a longer distance, more work can be done with a given force, or the needed force can be reduced.
SIMPLE MACHINES
INCLINED PLANE SCREWLEVER PULLEYWHEEL AND AXLE WEDGE
Other useful machines:gear, bevel gear, worm gear, rack and pinion, cam-wheel, crank and rod, chain, belt, ratchet
ENERGYThe capacity to do work
Potential Energy Ep = mgh (mad)Kinetic Energy Ek = 1/2 mv2
Change in Energy is Power applied for a Time
E1-E0= Pt = (Fd/t) x t = Fd = madBut under constant acceleration d = 1/2 at2
so, E = 1/2ma2t2 = 1/2mv2
CONSERVATION OF ENERGY
• THE TOTAL AMOUNT OF ENERGY IN THE UNIVERSE CAN NEITHER BE
INCREASED OR DECREASED