Mechanics

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Mechanics

• Physics project
• Name Tamara Hall
• Form 5B

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Power

• Power is the work done or energy converted per
  unit time.
• P E/t (where P-power, E- energy, t-time)
• The unit for power is the Watt (W). Large amounts
  of power are measured in kilowatts (kW) or
  megawatts (MW).
• 1W1Js-1 i.e. 1 watt of power is dissipated if 1
  joule of work is done or 1 joule of energy is
  transformed in 1 second.

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Friction

• Friction is the force that opposes the relative
  motion of surfaces in contact and of bodies
  moving through fluids.
• Friction increases with the roughness of the
  surfaces in contact.
• Friction can be reduced by smoother surfaces,
  grease and other lubricants, rollers, wheels and
  ball bearings.
• Whenever work is done against friction, heat is
  produced

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Diagram of a machine
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Machines

• A machine is any device which enables a force to
  be applied at one point to overcome another.
• The applied force is called the effort, E.
• The force moved or overcome is known as the load,
  L.
• There are many purposes for machines such as i.
  multiplying forces
• ii. transferring energy
• Electrical energy?an electrical
  motor?mechanical energy

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• iii. Transferring energy from one place to
  another
• iv. Increasing speed
• v. changing the direction of a force
• vi. Multiplying distance
• Examples of machines include levers, pully
  systems, bicycles and the forearm of humans.

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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
  moved to the effort applied
• Velocity ratio is the ratio of the distance moved
  by the effort to the distance moved by the load.
• efficiencymechanical advantage/velocity ratio
  x 100
• one factor which affect efficiency is friction.

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• Energy may be used more efficiently and
  economically in the Caribbean in forms such as
• Solar energy using solar water heaters. These
  produce abundant hot water and the cost is not
  too high. But they are not yet popular.
• Photovoltaic solar systems are getting close
  to the cost of generating electricity from fossil
  sources because of the intense sunlight and high
  cost of diesel.

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• Geothermal energy- Islands in the lesser Antilles
  are known to have potential for geothermal
  energy. Eg. Guadeloupe has a 4MW plant from
  shallow high temperature wells since 1984.
• Geothermal energy is capable of grid
  connection as relatively large amounts of energy
  can be generated from a single plant.
• Natural gas- natural gas as a source of energy is
  important in Trinidad and Tobago currently eg.
  Petrotrin. However, with the large oil companies
  entering into electricity generation it is
  possible that gas could replace oil as an
  alternative energy source in the Caribbean.

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Hydrostatics

• Pressure
• pressure is the force acting perpendicular to
  unit surface area.
• The SI unit is Nm-2 and is called the Pascal
• Pressure force/area
• Pressure in fluids
• pressure in fluids depend on depth below the
  surface and the density of the fluid.
• Pressure at the same depth acts equally in all
  directions.

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• Pressure is uniformly transmitted through a
  liquid. One example of this application is the
  use of the hydraulic jack. A hydraulic jack is
  two cylinders connected. Among these two
  cylinders one is small and one is large. If a
  force is applied to the small cylinder it would
  result in a given pressure and this pressure
  would be the same in the larger cylinder. Since
  the larger cylinder has a greater area the force
  emitted by it would be greater. The pressure
  remains the same but there is a greater force.

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The Manometer

• A manometer is a device used to measure
  excess gas pressure. A simple design is to seal a
  length of glass tubing and then bend the glass
  tube into a U shape. It is then filled with
  mercury so all trapped air is removed from the
  sealed end of the tube. It is then positioned
  with the curved region at the bottom and the
  mercury settles at the bottom.
• After this occurs, a vacuum is produced in
  the sealed tube and the open tube is connected to
  the system whose pressure is being measured. In
  the sealed tube there is no gas to exert a force
  on the mercury. The net result is that the column
  of mercury in the left (sealed) tube is higher
  than that in the right (unsealed) tube. The
  difference in the heights of the columns of
  mercury is a measure of the pressure of gas in
  the system.

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A manometer
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Archimedes Principle

• Archimedes principle states that when a body is
  fully or partially submerged in a fluid the
  upthrust equals the weight of the fluid
  displaced.
• An object will float if the upthrust is greater
  than the weight of the object. Eg. A cork
  floating in water
• An object will be partially submerged if the
  weight of the object equals the upthrust. Eg.
  Wood in water
• An object will sink if the upthrust is less than
  the weight of the object. Eg. When water is
  pumped into the tanks of a submarine the weight
  becomes greater than the upthrust and it sinks

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