happyphysics.com Physics Lecture Resources Prof. Mineesh Gulati Head-Physics Wing Happy Model Hr. Sec. School, Udhampur, J&K Website: happyphysics.com

Ch 7 Potential Energy and Energy Conservation © 2005 Pearson Education

7.1 Gravitational Potential Energy © 2005 Pearson Education

Gravitational Potential Energy for motion along a curved path Some expression for gravitational potential energy whether the body’s path is curved or straight © 2005 Pearson Education

Example 7.5 The total mass of throcky and his skateboard is 25kg. He starts from rest and there is no friction. The total mass of throcky and his skateboard is 25kg. He starts from rest and there is no friction. Find his speed at the bottom of ramp © 2005 Pearson Education

ANS: (a) K1=0 U1=mgR K2=1/2mv 2 U2=0 From conservation of energy. K1+U1=K2+U2 0+mgh= 1/2mv2 +0 © 2005 Pearson Education

7.2 Elastic Potential Energy The process of storing energy in deformable body such as a spring or rubber band in terms of elastic potential energy. The process of storing energy in deformable body such as a spring or rubber band in terms of elastic potential energy. A body called elastic if it returns to its original shape and size after being deformed. A body called elastic if it returns to its original shape and size after being deformed.

© 2005 Pearson Education Work done on a spring Work done by a spring © 2005 Pearson Education

if only the elastic force does work if forces other than the elastic force do work © 2005 Pearson Education

7.3 Conservative and Nonconservative Forces The force that offers this opportunity of two-way conversion between kinetic and potential energies is called a conservative force. The force that offers this opportunity of two-way conversion between kinetic and potential energies is called a conservative force. Conservative force is that their work is always reversible. Conservative force is that their work is always reversible. law of conservation of energy © 2005 Pearson Education

Properties of work done by a conservative force It can be expressed as the different between the initial and final values of a potential energy function. It can be expressed as the different between the initial and final values of a potential energy function. It is reversible It is reversible It is independent of the path of the body and depends only on the starting and ending points. It is independent of the path of the body and depends only on the starting and ending points. When the starting and ending points are the same, the total work is zero. When the starting and ending points are the same, the total work is zero. E=K+U is constant E=K+U is constant © 2005 Pearson Education

The Law of conservation of energy The energy associated with change in state of the materials is called internal energy The energy associated with change in state of the materials is called internal energy Friction Heat Friction does negative work and the change of internal energy of the block and surface is positive © 2005 Pearson Education

7.4 Force and Potential Energy force from potential energy, one dimension © 2005 Pearson Education Spring force

Gravitational force © 2005 Pearson Education

Force from potential energy Force and Potential energy in 3 Dimensions © 2005 Pearson Education

7.5 Energy Diagrams © 2005 Pearson Education

END Visit: happyphysics.com For Physics Resources