Flowers in Liquid Nitrogen
Energy
- Capacity to do work
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Light can be converted to heat energy which can apply a force and make something move. |
Radiometer
Gasoline is a form of energy
because it can do work.
by Don Ion
Levers give you a 'mechanical advantage'
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Work always involves some tradeoff. Name 2 ways 1st gear is different than 10th gear. |
1st gear requires
a small force and a lot pedaling,
while 10th gear requires
little pedaling but larger force.
An Incline Plane is a Simple Machine
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
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"Do the young man's HANDS do any work on the books he's holding?" |
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"No. The books do not move in the direction of the hand's force. (up) His legs do the work" |
Compound pulleys reduce the force
needed to do work.
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"What distance would the rope have to be pulled to make the weight rise 1 m ?" |
Moufle - Ilustración de un polispasto de cuatro poleas.
Copyright © 2004 CR. Imagen creada para la Wikipedia en Español.
(Borrar todas) (act) 09:40 7 ago 2004 (Ilustración de un polispasto de cuatro poleas.)
| W | = | F | Δd |
| (Nm) | (N) | (m) |
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"To lift the weight 1 m the rope has to be pulled 4 m. F reduced by 1/4, d increased by 4 times" |
Machines reduce force but
increase the distance the force is applied
by an equal magnitude.
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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?
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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)
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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 upward against the force of
gravity.
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"If AB/BC = 3, what is the smallest mass ball P could have?" (assume no friction)
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If W = 12 N, P could be as small as ....
J. L. Comstock A System of Natural Philosophy:
Principles of Mechanics
(: Pratt, Woodford, and Company, 1850) 92
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"Ball P could be 1/3 the mass of ball W" 4 N
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