Work and Energy Class 9 notes

WORK AND ENERGY
Class: 9 Notes




1

, WHAT WE WILL STUDY IN THIS
CHAPTER:


o Work
o Work Done against Gravity
o Work Done By a Force acting Obliquely
o Energy
o Kinetic Energy
o Potential Energy
o Power
o Commercial unit of Energy




2

, WORK


 In ordinary language the word “Work” means almost any physical or
mental activity but in physics it has only one meaning: Work is done when
a force produces motion.
For example: When an engine moves a train along a railway line, it is said
to be doing work:, a horse pulling the cart is also doing work in moving
himself against the force of gravity.
• Work is a Scalar Quantity.




3

, The work done by a force on a body depends on two factors:
a) Magnitude of the force
b) Distance trough which the body moves (in the direction of force)
We can now define work as follows: Work done in moving a body is equal to
the product of force exerted on the body and the distance moved by the
body in the direction of force. That is,
𝑊𝑜𝑟𝑘 = 𝐹𝑜𝑟𝑐𝑒 × 𝐷𝑖𝑠𝑡𝑎𝑛𝑐𝑒 𝑚𝑜𝑣𝑒𝑑 𝑖𝑛 𝑡𝑕𝑒 𝑑𝑖𝑟𝑒𝑐𝑡𝑖𝑜𝑛 𝑜𝑓 𝑓𝑜𝑟𝑐𝑒
But we usually write as:
𝑊𝑜𝑟𝑘 = 𝐹𝑜𝑟𝑐𝑒 × 𝐷𝑖𝑠𝑡𝑎𝑛𝑐𝑒
If a force F acts on a body and moves it a
distance s in its own direction, then:
𝑊𝑜𝑟𝑘 𝑑𝑜𝑛𝑒 = 𝐹𝑜𝑟𝑐𝑒 × 𝐷𝑖𝑠𝑡𝑎𝑛𝑐𝑒
or, 𝑊 = 𝐹 × 𝑠

4