3) bernoulli\'s principle of fluids stated that net work is the sum of differenc
ID: 1582492 • Letter: 3
Question
3) bernoulli's principle of fluids stated that net work is the sum of differences in kinetic energy and potential energy. But While I was studying the notion of work done by conservative and nonconservative forces they stated that net work is only the difference in kinetic energy while - delta PE is the work done by only conservative forces and the work done by non conservative forces was equal to the mechanical energy which is the sum of differences in kinetic energy and potential energy. Then according to what has been stated above why net work isn't equal to the work done by non conservative forces equal to the mechanical energy. I am a bit confused, can you explain to me the difference?Explanation / Answer
In the case of conservarive forces, the net work done on the object during any closed loop is zero. It is path independent.
In the case of non conservarive forces, there is a net work done on object during any closed loop. It is path dependent.
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In the case of conservative forces, the law of conservation of energy holds good, that is
Efinal = E initial
Energy is sum of change in potential energy and change in kinetic energy.
( KE ) final + ( PE) final = ( KE) initial + ( KE )initial
In the case of non conservative forces, this is not holds good, for such as case,
Efinal < E initial, here we need to add an explicit factor for work they do, that is
Efinal = E initial +Wnc
( KE ) final + ( PE) final = ( KE) initial + ( KE )initial +Wnc
Here, Wnc is work done by nonconservative force.
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Example: (1) Gravity acts on ball when we thrown upward is an exmple of consrvative force.
In the case of ball moving upward, gravity do a negative work -mgh and hence the ball slows down. While it returns, the gravity do positive work mgh . Hence, net work done by gravity is zero.
(2)
Friction is an exmple of nonconservative force
When an object move from two points on frictional surface, the work done by friction is double during complete one closed path ( some A to B and B to A ) . The net work is not equal to zero. The net work by friction over a closed path is not zero.
In our real work situations, most of nonconservative.
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In Bernoulli's principle derived on the basis of the principle of conservation of energy. According to this, in a steady flow, the sum of mechanical energy in a fluid alonng streamline is the same at all points on that streamline. It implies that sum of kinetic energy and potential energy remain constant.
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