<P> In the physical sciences , mechanical energy is the sum of potential energy and kinetic energy . It is the energy associated with the motion and position of an object . The principle of conservation of mechanical energy states that in an isolated system that is only subject to conservative forces , the mechanical energy is constant . If an object is moved in the opposite direction of a conservative net force , the potential energy will increase and if the speed ( not the velocity ) of the object is changed , the kinetic energy of the object is changed as well . In all real systems , however , nonconservative forces , like frictional forces , will be present , but often they are of negligible values and the mechanical energy 's being constant can therefore be a useful approximation . In elastic collisions , the mechanical energy is conserved but in inelastic collisions , some mechanical energy is converted into heat . The equivalence between lost mechanical energy ( dissipation ) and an increase in temperature was discovered by James Prescott Joule . </P>
<P> In the physical sciences , mechanical energy is the sum of potential energy and kinetic energy . It is the energy associated with the motion and position of an object . The principle of conservation of mechanical energy states that in an isolated system that is only subject to conservative forces , the mechanical energy is constant . If an object is moved in the opposite direction of a conservative net force , the potential energy will increase and if the speed ( not the velocity ) of the object is changed , the kinetic energy of the object is changed as well . In all real systems , however , nonconservative forces , like frictional forces , will be present , but often they are of negligible values and the mechanical energy 's being constant can therefore be a useful approximation . In elastic collisions , the mechanical energy is conserved but in inelastic collisions , some mechanical energy is converted into heat . The equivalence between lost mechanical energy ( dissipation ) and an increase in temperature was discovered by James Prescott Joule . </P>
when is the mechanical energy of a system conserved
when is the mechanical energy of a system conserved
elastic collisions
elastic collisions