Mechanics
Mechanics
Physics project
Name: Tamara Hall
Form: 5B
Power
Power
•Power is the work done or energy convertedper unit time.
•P= E/t (where P-power, E- energy, t-time)
•The unit for power is the Watt (W). Largeamounts of power are measured in kilowatts(kW) or megawatts (MW).
•1W=1Js-1 i.e. 1 watt of power is dissipated if 1 joule of workis done or 1 joule of energy is transformed in 1 second.
Friction
Friction
•Friction is the force that opposes the relativemotion of surfaces in contact and of bodiesmoving through fluids.
•Friction increases with the roughness of thesurfaces in contact.
•Friction can be reduced by smoothersurfaces, grease and other lubricants, rollers,wheels and ball bearings.
•Whenever work is done against friction, heatis produced
Diagram of a machine
Machines
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iii. Transferring energy from one place toanother
iv. Increasing speed
v. changing the direction of a force
vi. Multiplying distance
•Examples of machines include levers, pullysystems, bicycles and the forearm ofhumans.
Efficiency of Machines
Efficiency of Machines
•efficiency of a machine= energy input / energy output
= work output/ work input
= power output/ power input
•Mechanical advantage is the ratio of the load movedto the effort applied
•Velocity ratio is the ratio of the distance moved bythe effort to the distance moved by the load.
•% efficiency=mechanical advantage/velocity ratio x 100
•one factor which affect efficiency is friction.
•Energy may be used more efficiently andeconomically in the Caribbean in forms suchas:
•Solar energy using solar water heaters. Theseproduce abundant hot water and the cost isnot too high. But they are not yet popular.
Photovoltaic solar systems are getting closeto the cost of generating electricity fromfossil sources because of the intense sunlightand high cost of diesel.
•Geothermal energy- Islands in the lesser Antilles areknown to have potential for geothermal energy. Eg.Guadeloupe has a 4MW plant from shallow high temperaturewells since 1984.
Geothermal energy is capable of grid connection asrelatively large amounts of energy can be generatedfrom a single plant.
•Natural gas- natural gas as a source of energy isimportant in Trinidad and Tobago currently eg.Petrotrin. However, with the large oil companiesentering into electricity generation it is possible thatgas could replace oil as an alternative energy sourcein the Caribbean.
Hydrostatics
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•Pressure is uniformly transmitted through a liquid.One example of this application is the use of thehydraulic jack. A hydraulic jack is two cylindersconnected. Among these two cylinders one is smalland one is large. If a force is applied to the smallcylinder it would result in a given pressure and thispressure would be the same in the larger cylinder.Since the larger cylinder has a greater area the forceemitted by it would be greater. The pressure remainsthe same but there is a greater force.
The Manometer
A manometer is a device used to measure excess gas pressure. Asimple design is to seal a length of glass tubing and then bendthe glass tube into a U shape. It is then filled with mercury soall trapped air is removed from the sealed end of the tube. It isthen positioned with the curved region at the bottom and themercury settles at the bottom.
After this occurs, a vacuum is produced in the sealed tube andthe open tube is connected to the system whose pressure isbeing measured. In the sealed tube there is no gas to exert aforce on the mercury. The net result is that the column ofmercury in the left (sealed) tube is higher than that in the right(unsealed) tube. The difference in the heights of the columns ofmercury is a measure of the pressure of gas in the system.
A manometer
Archimedes Principle
•Archimedes principle states that when a body is fullyor partially submerged in a fluid the upthrust equalsthe weight of the fluid displaced.
•An object will float if the upthrust is greater thanthe weight of the object. Eg. A cork floating in water
•An object will be partially submerged if the weight ofthe object equals the upthrust. Eg. Wood in water
•An object will sink if the upthrust is less than theweight of the object. Eg. When water is pumped into the tanksof a submarine the weight becomes greater than the upthrust and itsinks
