“If a man will begin with certainties, he shall end in doubts;
but if he will be content to begin with doubts, he shall end in
certainties.”
― Francis Bacon, The
Oxford Francis Bacon IV:
The Advancement
of Learning
Flowers in Liquid Nitrogen
Energy
- Capacity to do work
Show Me The Physics
YouTube
Channel
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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'
[ Flash ]
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Work always involves some tradeoff. Name 2 ways 1st gear
is different |
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
[ Flash ]
I) Work - when a force F acts parallel to the motion of an object over a distance d.
Work is positive when the force acts in the same direction as the object's motion ...
(When the weight is lifted up)
and negative if
the force acts opposite
to the direction of the object's motion.
(When the weight is brought down)
Work and Energy
**Scalar**
(means direction doesn't count)
1 + 1 always = 2
A) Equation
| W | = | F | Δd |
| (Nm) | (N) | (m) |
F - force
acting
parallel to the 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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