Work,energy and power

Work,energy and power

1. work done and energy

   • W= the product of force and the distance moved in that direction
     • W=Fx
     • W= to energy transferred
     • Nm or j
   • E= the capacity for work done
   • work done at an angle to motion (w=Fxcostheta)

2. 5.4-power and efficiency

   • power=rate of work done
     • Js^-1
     • W
   • P=W/t
     • As W=Fx
       • P=Fx/t
         • P=Fv
   • % Efficiency=useful output/total input x100

3. 5.2-Conservation of energy

   • forms of energy
     • Kinetic
       • due to motion of an object with mass
     • Gravitational potential
       • due to objects position in a gravitational field
     • Chemical
       • Contained within the bonds between atoms
     • Elastic potential
       • due to a reversible change in shape
     • Electrical potential
       • energy of electrical charges due to their position in an electrical field
     • Nuclear
       • E within the nuclei of atoms
     • Radiant
       • E stored in the oscillating Electric and magnetic fields of EM waves
     • Sound
       • E of mechanical waves due to movement of atoms
     • internal/thermal
       • The sum of random potential E and Ke of atoms in a system
   • The C.O.E principle
     • total energy in a closed system remains constant: energy can never be created or destroyed, just transferred.

4. 5.3-Ke and Gpe

   • Ke=1/2mv^2
   • as W=Fx
     • Gpe=mgh
   • in a closed system mgh=1/2mv^2
     • m=const
       • gh=1/2v^2
         • v^2=2gh
           • v=rt(2gh)