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
Car
Engine
-
Physics Flash
Animations
by Don Ion
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 this young man 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. displacement plot is equal to work
W = Area under plot
= 1/2bh
= 1/2(5 m)(3 N)
7.5 Nm