Energy Notes

Energy
- Capacity to do work

Light can be converted to heat energy
which can apply a force
and make something move.

Gasoline has energy because it can do work

I) Work - when a force causes an object to move in the direction of that force.

Work and Energy

**Scalar**

(means direction doesn't count)

1 + 1 always = 2

A) Equation

W	=	F	Δd
(Nm)		(N)	(m)

F - force acting in
same direction as motion

Δd - displacement

Other units for work (Joule) or Kg m²/sec²

Challenge Question: Two people exert a 10 Newton force on a block for 2 meters. One person exerts her force at a 50-degree angle.

Person 1

Person 2

Did both people do the same work???

Person 2 does more work
All of her force goes to
moving the block

Does these young man's ARMS do any work
on the books he is holding?

No. The books do not move
in the direction of the arm's force. (up)

Ex) A 20.0-N force is used to push a 2.00-kg cart a distance of 5.00 m. Work done on cart =

a)150. J b)100. J c)200. J d)40.0 J

Ex) A 20.0-N force is used to push a 2.00-kg cart a distance of 5.00 m. Work done on cart =

W	=	F	Δd
(Nm)		(N)	(m)

a)150. J b)100. J c)200. J d)40.0 J

B) Work and F vs. d diagram (plot)

Area under a
Force vs. d plot
= Work

W = Area under plot

= 1/2bh

= 1/2(5 m)(3 N)

7.5 Nm

Ramps reduce the force needed to move a body

J. L. Comstock A System of Natural Philosophy: Principles of Mechanics
(: Pratt, Woodford, and Company, 1850) 92