Chen Ning,
there you go :

Turning effect of a force:

Objectives
- learn the meaning of moment of a force
- examples of turning effect of forces in everyday life
- about different types of levers and their uses

What is a Moment?
- a moment is the turning effect of a force
- SI Unit for a moment is Newton-metre(Nm)

Factors affecting the moment of a force
the moment of a force depends on:
- size of the force
- perpendicular distance of the force from the turning point(pivot/fulcrum)
(photo)
Hand is far from the turning point so small force is required.
(photo)
Hand is too near the turning point, so large force is required.

Calculating the moment of a force
the moment of a force is calculated by:
FORMULA:
moment of a force = Force x perpendicular distance(from the force to the fulcrum)
---
when calculating moments of forces, it is important to describe each moment of a force as clockwise or anticlockwise

Example:
Gabriel applies a force of 5oN to open the door as shown below. If the distance of the handle from the hinges in o.5m, what is the moment of the force about the hinges?
(photo) Solution :
Moment about the hinges
= F x D
= 5oN x o.5m
= 25Nm(Anticlockwise)

Test yourself!!! :
A force of 1o N is applied to the spanner to tighten a nut. The length of a spanner is o.2m. What is the moment exerted when the force acts at the end of the spanner?
(photo) Solution:
Moment about the spanner
= F x D
= 1o N x o.2m
= 2Nm(clockwise)

Principle of Moments
A see-saw has clockwise moment and an anticlockwise moment. When the two moments are equal, the see-saw is balanced.
(photo)
The Principle of Moments states that when a body is balanced, the total clockwise moment about the pivot is equal to the total anticlockwise moment about the same pivot.
Simply,
Anticlockwise moment = Clockwise moment (remember this)
Defination: The Principle of Moments states that when a system is balanced, anticlockwise moment equals clockwise moments.

Machines
- a device that helps us to do work more easily.
- Examples:
> tools like scissors, can-openers, spanners etc.
> large complex machines like drilling machines, excavators etc.
- The simplest machine is the lever.

Levers
- a lever is a long rod that turns about a point called pivot/fulcrum.
- when a lever is used, a force called the effort is applied at one point of the lever to overcome another force called the load at another point.
- has 3 parts:
> an Effort(E)
> a Load(L)
> a Fulcrum(F)

Levers make use of turning effect of forces to produce.....
- a large force from a small force(effort)
- a large movement from a small movement.

First Class Levers
(photo)
- Fulcrum(F) is between the load(L) and effort(E). <EFL>
- Examples:
> scissors
> pliers
> claw hammer
- a small force produces a large force.
- a large movement by the effort produces a small movement by the load.
(photo)
the crowbar shown above increases the effort so that a large force is produced to pry open the lid of the box.

Second Class Levers
(photo)
- the load(L) is between the fulcrum(F) and the effort(E). <LFE>
- Examples:
> wheelbarrow
> nut cracker
> bottle opener
-a small force produces a large force.
(a small effort produces a large load)
- a large movement by the effort produces a small movement by the load.
(photo)
the nutcracker shown above has a long handle. the effort at the end of the handle produces a large force to break the nut.

Third Class Levers
(photo)
- the effort(E) is between the fulcrum(F) and the load(L). <FEL>
- Examples:
> broom
> fishing rod
> stapler
- a large effort produces a small force.
- a small movement by the effort produces a large movement by the load.
(look at the movement instead of the effort.)
(photo)
in the fishing rod shown above, when the effort moves through a short distance. the load moves through a large distance.

Levers in the body
- many of the moving parts of the body are actually levers.

Arm & elbow:
(photo of arm)
(photo of arm AGAIN)
the arm is a third-class lever because the effort is between the fulcrum and load.

Ankle & foot:
(photo of foot)
the foot is a second-class lever because the load is between the fulcrum and effort.

--- End of Notes ---

the RED words are blanks in the notes. (:

Wah,
finally sia.
eh,
i show you the photos tomorrow. (:
JIAYOU in doing the science worksheet!! (:
Hahas.