1. Regents Physics Unit VI: Work, Power & Energy
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2. Part I: Work

3. 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

4. Work F d

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

7. 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

8. Since , then the units of work are Joules

9. 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

10. 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.

11. 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.

12. 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 m. How much work does the player do on the puck?

13. 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

14. 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:

15. 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

16. Part II: POWER

17. 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

19. 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!

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

21. 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.

22. 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?