Download 02 Effeciency and AMA

02 Effeciency and AMA
May 28, 2013
6 Simple Machines
Using the words below, fill in the space with the correct term for the defined machine
Screw
Wheel for Wheel and Axle
Pulley
Wedge
Inclined Plane
Lever
A ____________ is a simple machine that consists of a rigid object (often a bar of some kind) and a fulcrum (or pivot). Applying a force to one end of the rigid object causes it to pivot about the fulcrum, causing a magnification of the force at another point along the rigid object. There are three classes of ____________ , depending on where the input force, output force, and fulcrum are in relation to each other. Baseball bats, seesaws, wheelbarrows, and crowbars are types of ____________ . A ____________ is a circular device that is attached to a rigid bar in its center. A force applied to the ____________ causes the axle to rotate, which can be used to magnify the force (by, for example, having a rope wind around the axle). Alternately, a force applied to provide rotation on the axle translates into rotation of the ____________ . It can be viewed as a type of lever that rotates around a center fulcrum. Ferris ____________ , tires, and rolling pins are examples of ____________ . An ____________ is a plane surface set at an angle to another surface. This results in doing the same amount of work by applying the force over a longer distance. The most basic ____________ is a ramp; it requires less force to move up a ramp to a higher elevation than to climb to that height vertically. The wedge is often considered a specific type of ____________ . A ____________ is a wheel with a groove along its edge, where a rope or cable can be placed. It uses the principle of applying force over a longer distance, and also the tension in the rope or cable, to reduce the magnitude of the necessary force. Complex systems of ____________ can be used to greatly reduce the force that must be applied initially to move an object. A ____________ is a double­inclined plane (both sides are inclined) that moves to exert a force along the lengths of the sides. The force is perpendicular to the inclined surfaces, so it pushes two objects (or portions of a single object) apart. Axes, knives, and chisels are all ____________ . The common "door ____________ " uses the force on the surfaces to provide friction, rather than separate things, but it's still fundamentally a ____________ . A ____________ is a shaft that has a in inclined groove along its surface. By rotating the ____________ (applying a torque <http://physics.about.com/od/glossary/g/torque.htm>), the force is applied perpendicular to the groove, thus translating a rotational force into a linear one. It is frequently used to fasten objects together (as the hardware ____________ & bolt does), although Babylonians developed a "____________ " that could elevate water from a low­lying body to a higher one (which later came to be known as Archimedes' ____________ ). 1
02 Effeciency and AMA
May 28, 2013
Machines often lower the required force (Mechanical Advantage) when doing work BUT require more work to be done by the worker than the minimum required (Efficiency)
refer to Table 5.1 on page 181
AMA =
FL
FA
Efficiency =
W on the object
W you did
Machine
Efficiency (%)
Electric Motor
Gas Furnace
Wind Generator
Diesel Engine
Car Engine
Fluorescent Light
Incandescent Light
Questions
1. A portable stereo requires 265 J of energy to operate the CD player, yielding 200 J of sound energy.
a) How efficiently does the stereo generate sound energy?
b) Where does the "lost" energy go?
2. A force of 300 N is required to slide a 50 kg mass up an inclined plane that is 2.0 m long and 1.0 m long. a) How much work was done sliding the mass up the ramp?
b) How much energy did the mass gain?
c) How efficient was this machine?
d) What mechanical advantage was gained by using the ramp?
3. A pulley system is created that requires a force of 123 N to raise a 20 kg mass 50 cm.
a) How much work was done sliding the mass up the 50 cm?
b) How much energy did the mass gain?
c) How efficient was this machine?
d) What mechanical advantage was gained by using the pulley?
4. A 49.0 kg child sits on the top of a slide that is located 1.80 m above the ground. After her descent, the child reaches a velocity of 3.00 m/s at the bottom of the slide. Calculate how efficiently the potential energy is converted to kinetic energy?
1a) 75% 2a) 600 J b) 490 J c) 82% d) 1.6 3a) 61.5 J b) 98 J c) 63% d) 1.6 4. 26%
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