Transcript Work/Energy
ENERGY • The measure of the ability to do work • Conservation of energy -energy can change forms but can not be destroyed -the total amount of energy in the Universe remains constant!!!!!!!!!!!!!!!! -matter acts the same way (total amount remains constant) **Energy is measured in Joules (label, unit) Potential and Kinetic Energy • Potential energy of an object -stored, ready to use energy -could be because of chemical composition -could be because of position of the object -to calculate chemical potential energy of an object --measure the amount of chemicals in the object The amount of potential energy an object contains is the amount of work the object could do to another object -to calculate position energy of an object -measure mass x 9.8m/s2 x height lifted kilogram x gravity(use 10) x meter balance scale x constant x meter stick Kinetic energy of an object -determined by an object’s motion -kinetic energy is the work an object is doing on another object -to calculate motion energy • ½ x mass x velocity x velocity .5 x kg x (speed and direction)2 meters/seconds Velocity is a vector -vectors explain magnitude and direction of an object’s motion -magnitude --how fast -direction --which way -used to predict where the object will be in the future (graph) • The potential energy of an object is equal to the kinetic energy or work that it takes to gain that energy • Then it will have that much potential energy to use • Other examples 1 2 3 4 Work and Energy • The label for energy and work is Joule • Joule = Newton x meter force x distance -to find distance --measure with a meter stick -to find force --use a spring scale -force is an amount of weight -gravity pulling on mass creates weight (force) The word work is interchangeable for the words potential and kinetic energy • Mass x gravity = force • Kilogram x 9.8m/s2 = Newton • For work to be done, the object must move in the direction of the applied force Problems to do • Kinetic energy problems -1/2MV2, Joules 1) M = 2kg, V = 10m/s, V = North KE or work being done = ? Joules 2) Meters = 2, seconds = 1, Mass = 4kg. down KE or work being done is = ? Joules • Potential energy problems --mgh, Joules 3) mass = 10kg., height = 5 meters PE or Work it can do is = ? Joules Energy/ Work Problem F X D, Joules (Newton Meters) 4) Force = 30 Newtons, Distance = 5 meters Work or Energy = ? Joules 5) Mass = 10kg., distance = 10meters Work or Energy = ? Joules Power • Rate of work done • To calculate -work/time (work divided by time) • Work / time Joule seconds Newton X meter force distance Kilogram X 9.8m/s2 mass X acceleration rate due to gravity • Power is measured in Watts -label • Kilowatt hour -how much energy is used in an hour -how electric bill is calculated • Power Problem –Work/time, Watts 6) Workdone = 150Joules, time =50seconds Power = ? 7) Force = 20Newtons, distance = .5meters, time = 1 hour (seconds) Power = ? Answers 1) 2) 3) 4) 5) (.5) x (2) x (100) = 100Joules, North (4kg) x (2/1 = 22 = 4) x (.5) = 8Joules, down (10) x (9.8) x (5) = 490Joules (30) x (5) x = 150Joules (10kg.) x (9.8) x (10) = 980Joules Force 6) 150/50 = 3Watts 7) (20Newtons)x(.5meters)/3600sec.=.0028Watts 60sec. In a min.X 60min. In an hour = 3600sec.