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Work Power and Energy

Work Power and Energy. By, Dr. Ajay Kumar School of Physical Education D.A.V.V. Indore. Work. Machine are designed to do work. Simple machine such as the lever or wheel are the devices which are designed to perform work more efficiently.

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Work Power and Energy

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  1. Work Power and Energy By, Dr. Ajay Kumar School of Physical Education D.A.V.V. Indore

  2. Work • Machine are designed to do work. • Simple machine such as the lever or wheel are the devices which are designed to perform work more efficiently. • In each instance the machines aids in the use of a force to overcome a resistance efficiently. • When the resistance is overcome for a given distance , work is done.

  3. Definition of Work • Mechanically speaking, “ work is the product of the amount of force expended and the distance through which the force succeeds in overcoming a resistance it acts upon.”

  4. Equation for Work W = F X d • Where W = Work F = Force d = Distance

  5. Unit of Work • Unit for expressing work are numerous. • In English system the foot – pound is the most common unit. • Joule is the most frequently used unit in metric system. • A joule is equivalent to 107 x one gram of force exerted through one centimeter.

  6. Work (Cont) • In computing work, the distance “d” must always be measured in the direction the force acts. • Work done in the same direction that the body moves or Concentric movement is called as positive work. • Work done in the opposite direction or eccentric movement is called negative work.

  7. Work (Cont) • Negative forces resisting gravity perform less work over a given distance than positive forces overcoming gravity. • Example: One perform more work walking up a mountain the walking back down.

  8. Work (Cont) • When the exertion of effort produces no motion, mechanically speaking no work is done. • The physiological measures of such efforts may be determined by obtaining energy cost. This is usually measured by computing the amount of oxygen consumed during the effort and converting it to calories per minute.

  9. Power • Any measures of work does not account for the time involved in performing the work. • The rate at which work is done is called power and may be expressed as: P = Fd / t or P = W / t Where, P= Power, F = Force, d = Distance, W = Work, t = Time

  10. Power (Cont) • From the equation it is clearly evident the the machine or person who perform more work in a given time is more powerful. • In english system power is expressed as Foot-Pound / Sec or Horse power ( 1 Horse power = 550 Ft-lb / sec) • In metric system the unit is watt, which is equivalent to one Joule / Sec

  11. Energy • Energy is defined as capacity to do work. • A body is said to posses energy when it can perform work. • Energy may take numerous form, and can be converted from one form to another. • According to the Law of Conservation of Energy it can neither be created nor destroyed.

  12. Energy (cont) • Energy = the capacity to do work (scalar) • Types of energy: mechanical, chemical, heat, sound, light, etc • In sports we are most interested in mechanical energy

  13. Mechanical Energy • Kinetic Energy (KE) - energy due to motion • e.g. a diver (mass = 70 kg) hits the water after a dive from the 10 m tower with a velocity of 14 m/s. How much KE does she possess? • KE = ½ mv2= ½ x70 kg(-14 m/s)2 = 6860 J

  14. Mechanical Energy • (Gravitational) Potential Energy (P.E.) • – energy due to the change of position in gravitational field PE = mgh h = height of something above some reference line m = mass g = acceleration due to gravity (–9.81 m/s2)

  15. Potential Energy: • Note: in the absence of air resistance and other resistive forces, PE can be completely converted to KE by the work done by gravity on the way down. • e.g. a diver on top of a 10 m tower has a positive PE compared to water level • PE = –mgh = –(70 kg) x (–9.81 m/s2) x (+10 m) = 6860 J

  16. Mechanical Energy • Strain or elastic energy (SE) • – energy due to deformation • – this type of energy arises in compressed springs, squashed balls ready to rebound, stretched tendons inside the body, and other deformable structures SE

  17. Work-Energy Relationship • The work done by the net force acting on a body is equal to the change in the body’s kinetic energy • This relationship is true as long as there is no change in vertical position.

  18. The kinetic energy of a body is the energy due to its motion. The faster a body moves the more kinetic energy it posses. When a body stops moving the kinetic energy is lost. This is easily seen in the equation of kinetic energy. • K.E. = ½ mv²

  19. According to the principle of the conservation of energy the work done is equal to the kinetic energy acquired and therefore • FD = ½ mv² • This relationship is extremely helpful in explaining the situation when receiving the impetus of any moving object.

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