ESTIMATION! A skill every engineer should cultivate

How many ping-pong balls can fit into this room? Timer

Time to solve problem Accuracy of answer Detailed analysisEstimation

Vol = d 3 = 1 Vol = (4/3  d/2) 3 =.52

Estimation is… Quick models + Quick measurements + Quick calculations

Estimation Keep things simple…very simple

An estimation challenge What does a 5 gallon pail of liquid weigh? Density of water: 1.0Kg/L or 1 pound/pint (“a pint’s a pound”) 1 gallon = 8 pints = 8 lbs 5 gallon pail = 5 x 8 = 40 lbs (4% error, exact = lbs) Or…1 qt ~ 1 liter  4 qts/gal  5 gal = 20 qts ~ 20 liters  20 Kg (1 Kg/L)  20 Kg x 2.2 lb/Kg = 44 lbs (5% error) Timer

1. Observation Notice the chairs (size/material/strength) Notice a pop can (material/thickness/how- formed) Notice a staple (how it changes shape/how it grips the paper)

2. Model the physics…simply F = mA Everything is a cantilevered beam Coffee cup is 1-D heat transfer Vibration is 2 nd order DEQ Pendulum is small angle

An estimation challenge Each time an automobile tire turns, the tire material flexes and extends in a stress cycle as it takes the weight of the car. How many stress cycles does an average automobile tire go through each year? Timer

3. Measurements Develop a set of self-calibrations over wide range Time, length, weight, velocity, … Low extreme, middle (human experience), high extreme For middle range, used body-centered measuring tools No need to run to rulers or scales

TIME 1 ns(time it takes light to travel a foot) 100 ms(human reaction time) 0.5 s(4 ft drop of an object) 1 s("a-thousand-one-a-thousand-two.....") minutes, hours, days, years(you know these)

FREQUENCY 4 Hz(beat with your hands) 440 Hz(concert A on the piano) 1 KHz(high for a mechanical resonance 92.5 MHz(your favorite FM radio station) 500 MHz(digital IC switching frequencies)

LENGTH 0.5 micron (modern IC feature) 70 micron (human hair) (.003").004 in (paper thickness) 1 in(quarter) (actual = a little over 15/16") 6 in(dollar) (actual = 6 3/32") 9 in(my finger span) 1 ft (standard floor tile) 6 ft(my outstretched arms) 100 m(football field) 1 mi(4 times around the track, 1 min in a car) 240,000 mi (distance to moon) 92 million mi (distance to sun)

VELOCITY 1 fps(follow your finger) 60 mph(car) 200 mph(airplane take off speed) 3E8 m/s(speed of light)

ACCELERATION 0.3 g(car 0-60 in 10 sec) 0.6 g(airplane in 15 sec) 1.0 g(earth) 6.0 g(30-0 mph in ¼ sec) 200 g(4 ft drop test, 0.25 inch crush zone) ???(fast elevator)

FORCE/WEIGHT 1 oz(4 quarters? Measure it (weigh a roll)) 1 lb(box of nails, tub of coleslaw, pint of water) 10 lbs(big bag of flour) 25 lbs(bag of dog food) xxx lbs(body weight) 1 ton(a car) ????(big trucks) ????(airplane, ships)

TORQUE 1 ft-lb(12” bar with tub of cole slaw hanging off the end 200 ft-lb(me hanging off a 15” bar) PRESSURE 4.3 psi(10 ft column of water, water is ½ psi per foot) 9 psi(playground ball) 14.7 psi(ground level air pressure) 100 psi(pneumatic automation, shop air) 5000 psi(high pressure hydraulics)

Pressure at your outdoor tap? Hose shoots about 30 ft up Water is ½ psi per foot  water is 15 psi at nozzle Assume shooting process 50% efficient  water is about 30 psi inside hose

An estimation challenge How many gallons of water flow under the Washington Avenue bridge each hour? Timer

3. Calculations What a good estimator thinks of calculators….

Round off 8 = = fps 2 = 30 pi = 3

Conversions 25 Microns =.001 in. 1 mph = 1.47 fps 1 atm = 14.7 psi = 760 mmHg 1 g = 32.2 fss 1 BTU = 778 ft-lbs 1 hp = 550 ft-lbs/s = 746 watts 1 lb = 4.4 Newtons Or, remember equivalent points on scale: 32 deg F = 0 deg C (-40 = -40) 15 mph = 22 fts = 264 ips 60 mph = 88 fps 1/2 psi = 1 ft of water

If you don’t know the units…. EXAMPLE: Someone says, “The pressure needed to promote skin breakdown is 100 mmHg” try

How to become better Give yourself estimation problems all the time Start memorizing conversions Build a personal library of measurements Be familiar with simple physics models And… THROW AWAY YOUR CALCULATOR!

An estimation challenge How high can I be lifted by the energy in a 9v battery? (I weigh about 165 lbs) Timer

Some to take home What’s the weight of the stainless steel skin on the Weisman Museum? What’s the pressure under each leg of your desk chair? How many times is the ‘e’ key pressed in the 3 year lifetime of a computer? How long does it take to make an ice cube? What’s the bite pressure on your teeth when eating an apple? What’s the volume of a ton of bricks?

POWER 1 watt(flashlight bulb) 100 watt(bright house bulb) 10,000 watt(movie lamp) 200 hp(big car engine ENERGY 80 ft-lbs(PE of you standing) 5 watt-hrs(fresh 9v alkaline battery)