University:
Winston-Salem Forsyth County Schools
Course:
AP Physics I
Academic year:

2014
Views:

101

Pages:

16
Author:

Karina Hinton

Potential Energy Golf Ball Lab Follow Up You had a golf ball with a mass around .045kg. You drop it from .20 meters. The more potential energy, the larger the impact (harder it falls) 1. If you then drop a fake golf ball with a mass of .012kg, do you have to drop it from a higher or lower height to get the same amount of energy? Explain why 2. How much Kinetic Energy does the .045kg ball have right before it hits the sand when you drop it from .2 meters up? You can actually use your PE =mgh to figure this out. Work, Power, & Machines Hold a book out in front of you…your arms are getting tired…is this work? What is work ?  WORK: Using a force to move an object a distance (in the same direction). Calculating Work Work = Force x Distance The force acts in the direction of the movement. Work  Work does NOT involve time, only force and distance. Work = Force x Distance  No work is done when you stand in place holding an object. – Example: W = F x D – work = 40N x 0m = 0 zero Is work being done or not?  Mowing the lawn  Weight-lifting  Carrying furniture from one room to another  Pushing against a locked door  Swinging a golf club  Hanging from a chin-up bar YES YES NO NO YES NO The Joule – the unit we use for work (and ENERGY!)  One Newton of Force moving 1 meter is known as a joule (J).  Named after British physicist James Prescott Joule. Calculating Work  If this kid pushed the chair across the floor 10 meters with 5N of force, how much work is done?  w=F x d  W= 5 x 10  50 Joules How quickly work is done. Amount of work done per unit time. POWER = WORK TIME See if you can figure this out... Talia and Chris have the same size yards. Talia can mow her yard in 1 hour with 30N Force, but it takes Chris two hours to mow his yard with 30N of force. 1. Who did more work? 2. Who used more power? They both did the same amount of work, but Talia used more power! The watt – the unit of power  A unit named after Scottish inventor James Watt.  Invented the steam engine.  P = W/t  Joules/second  1 watt = 1 J/s watts  Used to measure power of light bulbs and small appliances  An electric bill is measured in kW/hrs.  1 kilowatt = 1000 W A train pulls a load 20 meters with 3000N of force. How much work is done? W=Fd W= 3000 x 20 = 60,000 Joules A woman lifts a baby with 5N of force. She did 30J of work. How far did she lift the baby up? W= Fd 30= 5d 30/5 =d D=6 meters A kid pushed a wagon in 30 seconds with 20 N of force. He pushed it a total of 10 meters before he gave up. How much work did he do? W=20x10 = 200 J How much power did he use? P=W/t P=200/30 P= 6.67 W