Regents Physics Unit VI: Work, Power & Energy This presentation demonstrates the new capabilities of PowerPoint and it is best viewed in Slide Show. These slides are designed to give you great ideas for the presentations you’ll create in PowerPoint 2011! For more sample templates, click the File menu, and then click New From Template. Under Templates, click Presentations.

Part I: Work

What is Work? Where: W=work F=force d=distance or displacement **F must be parallel to d** *Work is a scalar In Physics, work is equal to a force exerted on an object in the direction of motion, times the object’s displacement

Work F d

“Spinning Your Wheels…” In other words, if the object doesn’t move, you do no work.

Fundamental Units: Derived Units: A Side Note on Units Units that use the SI: F for force Derived Units: Units that we give a name: (newton) for force

Since , then the units of work are Joules

Units of Work: The Joule A Joule is a derived unit (we gave N*m a name) [Work]= =F*d =[N*m] =[(kg*m/s2)*(m)] =[kg*m2/s2] =Joule! Joule= kg*m2/s2=N*m

The Joule (SI units) is equivalent to the Calorie (pre-SI units). What is a Joule? The Joule (SI units) is equivalent to the Calorie (pre-SI units). *There are kilocalories (capital C) and calories (lower case c). You intake “Calories” every day. Without eating you would be weak and you wouldn’t have much energy… It turns out that the Joule(Calorie/calorie) is a unit of Energy.

What is a Joule? (Cont’d) One “food” Calorie = 4,180 Joules A Snickers bar has about 280 Calories, or 1,170,400 Joules. So…Doing “Work” on something changes its total energy. We’ll come back to this later.

Work: An example problem A 105 kg hockey puck is sliding across the ice. A player exerts a constant 4.5 N force over a distance of 0.150 m. How much work does the player do on the puck?

Work @ an angle In the real world, forces aren’t always applied parallel to the motion of an object. Again, we need to think about the “use-ful” and “use-less” forces. θ

Work @ an angle (cont’d) Formulas: You can derive formulas each time using SOH-CAH-TOA Or you can memorize these: For “Horizontal Work”, For “Vertical Work”, These formulas work if the Θ is the angle between the force and the horizontal. *Hint: You might want to write these down here:

Work @ an angle: example problem This box is being pulled with a force of 30 N at an angle of 60 degrees for 6 m. Determine the work done on the box. F 60° d

Part II: POWER

If you refer to your reference tables, you’ll see that: What is Power? Power is Work divided by time, or in other words, the rate at which work is done. (Or the rate at which energy changes) If you refer to your reference tables, you’ll see that: Where P=power, W=work, F=force, d=distance, and v=average velocity *Power is a scalar quantity

The unit of Power is the Watt. Units of Power The unit of Power is the Watt. We use the letter W to represent the unit Watt (don’t confuse it with W for work on the reference tables) Watt=Joules/seconds Watt? Don’t worry, Joule get it in a second!

Units of Power (Cont’d) Watt= =J/s =(kg*m2/s2)/s =(kg*m2/s3) The fundamental unit for Watts: (kg*m2/s3)

Power Example Problem: When Justin Beiber lifts his love child, 1400 J of work is done in 2.5 s. Calculate how much power Justin develops.

Another Power Example Problem… Ndamukong Suh stomps on a player with a force of 750 N at an angle of 45 degrees. He pushes the player a distance of 1.5 m in .5 seconds. How much power did he deliver to the player?