حصريا : شرح درس Energy- علوم لمدارس اللغات للصف الاول الاعدادى

تاريخ التسجيل : 30/03/2010

Introduction

The need for energy increases with increasing development of the human societies, so as societies developed, a big change has occurred in the sources and needs of energy. Objectives:

Define energy .
Define work
Recognize examples of some forms of energy.
Mechanical energy.
The law of conservation of energy.

Work

The work necessitates the existence of a force which acts upon an object to move it for a certain distance.
Examples of work:

Someone lifting (raising) an object..
Someone pushing an object along a road.
The fall down of fruits from trees to the ground.

Factors affecting work:

The force:
- Work is directly proportional to the force.
- The work done to raise two books one meter high against the attraction force of the earth is double that needed for raising only one book up to the same height.
- This means that the work gets doubled by doubling the force.

The distance:

Work is directly proportional to the distance moved by the body.
The work done to raise a book one meter high is double that needed to raise it half a meter high.
This means that the work gets doubled by doubling the distance, consequently there is no work done as long as the force does not transfer objects from one place to another.

From this we conclude that :
Work = Force x Distance

Energy

Energy is the ability to do work..
Examples of energy:

The builder who lifts the building materials from the ground to higher floors has energy.
The fruits on the trees have energy because they do work when they fall down.
The running water has energy because it does work when it turns the turbines of the electric generators.
A twisted spring of a watch has energy because it does work which appears in the movement of the watch pointers..

There are many forms of energy: muscular, mechanical, thermal, chemical, electrical, sound and nuclear energy.