Work WORK is done only if a force F causes an object to move a distance D. WORK = F  D The units for work are Newton- meters (Nm) or Joules (J). 1 Nm = 1 J

Power James Watt, Englishman in the 1700’s, who needed a term to distinguish a “good” steam engine from a “bad” engine. Difference was time to do work. POWER is the rate of doing work. POWER = WORK/TIME The units for power are J/s or watts (W) 1 J/s = 1 W

Example Problems You exert a 100 N force to move a box 3 m in 4 seconds. How much work did you do on the box? What was your Power Output? W=300 J P=75 W 100 N Box 3 meters in 4 seconds

An electric pump lifts 5000 N of water from the bottom of a 6 m deep well in 1 minute. W=30,000 J P=500 W

Volunteer… Things to Ponder… If you push on the wall for 5 hours, then do you do any work on the wall? If you drop a book, is work done on the book as it falls? Two Volunteers… Who did more work? Who had the larger power output?

Harvard Step Test Teacher intro and safety demonstration (proper technique for stepping) Work done in 1 minute in the HST: W = F  d Force = weight in pounds converted to Newtons using 1 lb = N d = convert # of reps to meters Answer will be in Joules Power output: P = W/(60 seconds)

Post Mini Lab Questions Calculate the work you performed. Determine your power output. How many 150 W light bulbs could you keep burning? How many people like you would it take to match the power output of a 100 horsepower engine? (1 hp = W) How many horsepower are you worth? Electric energy (work) is selling for about $.07 per kilowatt-hour. How much was your activity worth?

Discussion Question Even 100 hp would make a pretty weak engine, so how do we get so much power from our cars? Where does this energy come from? Additional facts: U-235 fission bomb (Hiroshima) - 6.5*1016 kW Hydrogen fusion bomb - 4.9*1019 kW the Sun - 3.3*1023 kW

Energy The capacity to do work Three Main Types Kinetic Energy Potential Energy “Other”RadiantThermalInternal Over a field

Kinetic Energy Energy due to Motion KE = (1/2)mv 2 m = mass of the object in motion v = velocity of the object Example #1: 10 m/sKE = ?? 1000 kg Example #2: 20 m/sKE = ?? 1000 kg

Potential Energy Stored Energy Types Gravitational energy ~energy due to position PE = mgh m = mass of object g = acceleration due to gravity (10 m/s2) h = height of the object above some arbitrary point Chemical energy~ an example is the energy in gasoline, which is due to the position of atoms in gasoline molecules- Mechanical PE~ like a compressed string, or a stretched bow & arrow Electromagnetic PE~ for example, magnetic attraction and static cling

Example: