Date post: | 05-Aug-2015 |
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POTENTIAL ENERGY AND
ENERGY CONSERVATIONReported by:
Ida Lyn A. AzueloBSED Physics 3
Physics for Secondary Teachers 1
Gravitational Potential Energy
• Potential energy associated with a body’s weight and its height above the ground
m – mass of the bodys – displacementy - vertical componentsw – weight (mg)Fother - some forces acting on the body
m – mass of the bodys – displacementy - vertical componentsw – weight (mg)Fother - some forces acting on the body
The quantity (y1 –y2) is
negative, and Wgrav is
negative because the weight and
displacement are in opposite
direction.
Conservation of Mechanical Energy(Gravitational Forces Only)
Work- Energy TheoremWtot = ΔK = K2 - K1
Wtot = Wgrav = -ΔUgrav = Ugrav,1 - Ugrav,2
ΔK = -ΔUgrav K2 - K1 = Ugrav,1 - Ugrav,2
K1 + Ugrav,1 = K2 + Ugrav,2
If only gravity does work
Total Mechanical Energy of the System
E = K + Ugrav
Potentialenergy
kineticenergy
E1 = K1 + Ugrav,1 E2 = K2 + Ugrav,2CONSTANT
When only the force of gravity does work, the total mechanical energy is constant—that is, it is
conserved.
CONSERVATION OF MECHANICAL
ENERGY
Problem Sample
You throw a 0.145-kg baseball straight up, giving it an initial velocity of magnitude 20.0
m/s. Find how high it goes, ignoring air resistance.
When Forces Other Than Gravity Do Work
Wother + Wgrav = K2 - K1
Wgrav = Ugrav,1 - Ugrav,2
Wother + Ugrav,1 - Ugrav,2 = K2 - K1
K1 + Ugrav,1 = K2 + Ugrav,2
If forces other than gravity do work
Elastic potential energy
• The process of storing energy in a deformable body such as a spring or rubber band in terms of elastic potential energy.
• A body is called elastic if it returns to its original shape and size after being deformed.
The work done by all forces other than the gravitational force or elastic force equals the change in the total mechanical energy E = K + U of the system, where U = Ugrav
+ Uel is the sum of the gravitational potential energy and the elastic potential energy.
Conservative Force and
nonConservative Force
A force that offers this opportunity of two-way conversion between kinetic
and potential energies CFNFA force that is not conservative