Friday, 30 September 2011

CHAPTER 10 SIMPLE MACHINES

Unit 10.1 Levers

1. Lever

a) is a simple machine
b) enables a small effort to overcome a heavy load
c) can be used to lift heavy objects
d) makes work easier

2. A lever has three parts :

a) Fulkrum (F) - the turning point or pivot
b) Effort (E) - the force applied to overcome a resisting force called the load
c) Load (L) - the resisting force exerted by an object

Figure 10.1 Lever

3. Levers can be classified into

a) First class
b) Second class
c) Third class

4. First Class Lever


a) Fulcrum is between the effort and the load
b) Small effort is used to move a large load
c) Effort is further from the fulcrum than load the load is
d) Effort moves through a longer distance than the load


Figure 10.2 First Class Lever

EXAMPLES OF FIRST CLASS LEVER



Scissors


Claw Hammer


Lid opener

Figure 10.3 Examples of First Class Lever

5. Second Class Lever

a) The load is between the fulcrum and the effort
b) Small effort is used to move a large load
c) Effort is further from the fulcrum than the load is
d) Effort moves through a longer distance than the load


Figure 10.4 Second Class Lever

EXAMPLES OF SECOND CLASS LEVER

Wheel Barrow


Nutcracker


Bottle Cap Opener

Figure 10.5 Examples of Second Class Lever

6. Third Class Lever

a) The effort is between the fulcrum and the load
b) A large effort is used to move a small load
c) Load is further from the fulcrum than the effort is
d) The load moves through a longer distance than the effort


Figure 10.6 Third Class Lever

EXAMPLES OF THIRD CLASS LEVER


Figure 10.7 Examples of Third Class Lever

7. When we loosen a bolt using a spanner, a force that is applied has a turning effect on the spanner

8. This turning effect of a force is known as the moment of a force

Figure 10.8

9. In figure 10.8, 

a) It is easier to loosen the bolt if you hold the spanner at position P than Q because the turning effect is greater
b) It is also easier to loosen the bolt if a larger force is applied at P to cause a greater turning effect

10. The turning effect or moment of a force is influenced by

a) the magnitude of the force applied
b) the position of the force applied

11. The S.I unit for measuring the moment of force is Newton-metre (Nm).

Figure 10.9

12. The moment of a force can be calculated by using the formula below :

Moment of a force = Force x Perpendicular distance from the pivot to the force
(Nm)                             (N)                               (m)

13. The principle of moments can be represented by the following formula :

Load = Distance of load from the fulcrum = Effort x Distance effort from the fulcrum
(L)                                                                      (E)    


Unit 10.2 Appreciating the Innovative Efforts in the Design of Machines to Simplify Work


1. Human beings make use of the principle of lever to invent machines

2. Innovative efforts in inventing make our work easier

3. Complex machines help us to carry out difficult and tedious work

4. Examples of some machines that are based on the principle of levers are crane, typewriter, pedal bin, pliers, paper cutter and stapler                   

The end of chapter 10. #
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Thursday, 29 September 2011

CHAPTER 9 : STABILITY

GLOSSARY


1.Base (Tapak) - The lowest part of an object on which the object rests or is supported


2. Base area (Luas tapak) - The surface covered by the base


3. Centre of gravity (Pusat Graviti) - The point of an object at which the whole weight of the seems to act.


4. Equlibrium (Keseimbangan) - A state of balance


5. Point of intersection (Titik persilangan) - Point where two or more lines cut or crossed each other.


6. Stability (Kestabilan) - The ability of an object to remain in its original position when disturbed.


7. Stable (Stabil) - Not likely to topple or change position.


UNIT 9.1 : STABILITY


1. The point of equilibrium is the point where the whole weight of an object appears to act on.


2. It is the point in which an object can be balanced on and it is present in all objects.


Activity 1


Make a triangle, a circle and a rectangular and find the point of eqilibrium. 


3. The point of equlibrium of an object is actually the centre of gravity pf the object.


4. It is the point at which the Earth's gravity acts on an object.


Factors affecting the stability of an object


1. The position of the centre of gravity


"The lower the centre of gravity, the more stable the object"


2. The base area


"The wider the base area, the more stable the object"


UNIT 9.2 : IMPORTANCE OF STABILITY


1. The principle of stability is applied to many aspects of our daily life.


2. We are more stable when we are standing with our legs apart because the centre of gravity is lower and the base area is wider.


3. An old man increases his stability by using walking stick.


4. A crawling baby is stable because his centre of gravity is low and his base area is wide.


5. A crocodile is more stable than a giraffe because its centre of gravity is lower.


6. A giraffe stands with its legs wide apart to increase its base area and to lower its centre of gravity.


7. Animals with heavy bodies have shorter legs to lower their centre of gravity.


8. A racing car is stable because it has low centre of gravity, wide tyres and wide base area.


9. Engines of lorries and buses are heavy and are placed underneath the vehicles to lower their centre of gravity.


10. Laboratory apparatus such as Bunsen Burner, retort stand and measuring cyclinder have wide bases to increase stability.


11. Motorcycle riders bend their body forward when they are speeding. This is to lower the centre of gravity of the rider and his motorcycle.


12. To maintain the stability of a double-decker bus, passengers are advised to fill up the empty seats in the lower deck first.


13. Passengers in a boat are advised to sit down instead of standing so as to lower the centre of gravity the boat.


14. Extra wheels are attached to children's bicycle to increase their stability.
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CHAPTER 8 SUPPORT AND MOVEMENT

Unit 8.3 Appreciating the support system in living things

1. Without a suitable support system, many living things will not be able to live.

2. A suitable support system can

a) give us proper shape and posture
b) support the weight of our body
c) protect our organs from injury

3. A person who has injured one of his legs will need a crutch to help support his body weight

4. Whales can live in water because a great part of its body weight is supported by the buoyancy of water

5. If the whale is washed ashore, it will die because its body weight will crush its internal organs

6. Support systems in plants enable them to stay upright to receive sunlight to manufacture food
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Thursday, 29 September 2011


Chapter 8 Support and movement

Unit 8.2 Support systems in Plants

1. Plants on land can be divided into
a) woody plants
b) herbaceous plants (non-woody plants)

2. Woody plants with a single thick stem are called trees. Examples of trees are mango trees and angsana trees.

3. Woody plants with many branches close to the ground are called shrubs. Examples of shrubs are hibiscus shrubs and rose shrubs.

4. Cells of non-woody plants absorb and retain water in their cells making them firm and turgid.



Features


Herbaceous

Woody








Structure of stem










-Little woody  tissue with few xylem cells.



-Rings of hard woody tissue with compact secondary xylem cells


Support

-Supported by the turgidity of cells.
-Cannot support a heavy weight.

-Supported by woody tissues.
-Can support a heavy
weight.


Examples

Balsam plant, spinach

Durian tree, angsana tree



Table 8.1 : Comparison of the support systems in herbaceous and woody plants

5. Some plants develop special structures to give additional support or to climb other supports toget sunlight for photosynthesis.


Buttress root









·         Thick support roots that grow from the stem above the ground
·         These roots hold tree firmly to the ground, giving it extra support
·      Examples : Angsana tree, casuarinas tree, durian tree
Prop roots
                                    

·      Roots which grow from the stem or branches into the ground to support the plant
·      Examples : Banyan tree, pandan plant maize plant
Prickles


·      An outgrowth of the epidermis and can be easily removed from the stem
·      Examples : Rose shrub
Tendrils


·   Curly string-like structure modified from stems and leaves
·   Curl and twine round parts of other plants or object to help the plant to climb
·   Examples : Cucumber plant, bitter gourd plant, pumpkin plant
Thorns


·         Sharp modified branches that cannot be easily removed
·         Act as hooks to hold to supports
·         Examples : Bougainvillea shrub
Clasping roots











·      Roots that grip onto other plants or structures to get support
·      Examples : Money-plant, betel vine (sirih)
Stilt roots


·     Roots that develop from the main stem and grow into the ground for support
·     Examples : Mangrove tree



6. Aquatic plants cannot stay upright on land because their stems are non-woody and soft.

 
                                                                      Water hyacinth

Water lettuce

Hydrilla

7. Aquatic plants can stay upright in water because their weighs are supported by the buoyancy of water

8. Some aquatic plants have many air sacs (kantung udara) in their stems and leaves. These structures make them light so that they can float on water. Examples : Lotus, water hyacinth, water lettuce, elodea and hydrilla.

9. Some aquatic plants that float on water have tiny leaves to ensure that they are not disrupted by the flow of water. Examples : Hydrilla and elodea.

Posted by Ariena at 03:30  


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