Revision on Energy transformations

Made by :Dr. Niveen Fawzy

Mechanical energy• Energy: is ability to do work , or to make a

change• Work: is force applied on a body to

displace it (move it) a distance in the direction of force

• Mechanical energy• It’s energy of object due to it’s motion or

• position

• MECHANICAL ENERGY= • POTENTIAL ENERGY + KINETIC

ENERGY

When you lift an object, you do work. This work is stored in the object in the form of energy (Potential energy)

So, POTENTIAL ENERGY is the stored energy in object due to work done on it PE= mass x gravitational force x height

When the object falls down , the stored energy changes gradually into motion (Kinetic energy)

So, KINETIC ENERGY is the work done during the motion of an object

KE = ½ x mass x velocit

Mechanical energy of the body has a constant value

• The sum of potential & kinetic energies of an object under the effect of gravity is a constant value

The conservation law of mechanical energy

Steps: -Push with your hand gently the pendulum & leave itObservation:It will move on both sides around its original position (A)-Maximum velocity is at point (A)Explanation:-Work is done to push the ball & stored as P.E at point (C ),When you leave it , P.E is gradually changed into K.E till reaching point (A) all M.E=K.E, then gradually velocity decreases till reaches maximum height velocity is zero at( C&B) = maximum P.E

How is a swing similar to a pendulum? -When swing is pushed ,work done is stored in swing in form of P.E-While swing is moving , a gradual change occurs , as P.E is converted into K.E-When it passes by initial position , velocity is maximum , all M.E=K.E-When reaching maximum height, velocity is zero ,& all M.E =P.EConclusion:Object keeps its mechanical energy which alternates between potential & kinetic energies