Chapter 8 Support and movement

8.1 Support systems in animals

1. Endoskeleton

a) Also known as the internal skeleton

b) Located inside the body of all vertebrates including human beings, elephants and fishes.

c) Made up of either bones or cartilage

2. Functions of endoskeleton

a) Supports body weight and maintains body shape

b) Protects soft internal organs

c) Provides points for the attachment of muscles

d) Allows free movement of body and limbs

 

frog

Duck

Figure 8.1 Animals with endoskeleton

3. Exoskeleton

a) Also called the external skeleton

b) Hard outer skin or shell of intertebrates

c) Made of cuticle or calcium carbonate

d) Examples of animals : Centipede, ant and crab

4. Functions of the exoskeletons

a) Maintains body shape and support body wieght

b) Protects internal organs

c) Provides places for the attachment of muscles

d) Allows movement of body parts

snail

Beetle

Figure 8.2 Animals with exoskeleton

5. Hydrostatic skeleton

a) Consists of a muscular wall which encloses a body cavity that is filled with fluid

b) This body fluid pushes out and exerts pressure in all directiona

c) This body fluid pressure, called hydrostatic pressure gives support and shape to the animal

d) A type of support system for some invertebrates like earthworm, leech, jellyfish and caterpillar

6.Functions of the hydrostatic skeleton

a) Supports and maintains body shape as well as rigidity

b) Supports and protects internal tissues and organs

c) Allows invertebrates to bend, straighten and move

Jellyfish

Earthworm

Figure 8.3 Animals with hydrostatic skeleton

7. The entire body weigh of land vertebrates is supported by the endo skeleton. So they have large and strong skeletons.

8. Land vertebrates have a long column of backbone, strong and big pectoral and pelvic girdles to support their body weight.

9. Birds have hollow bones to enables them to fly.

10. Advantages of hollow bones :

a) Light and strong

b) Allow vertebrates to move faster

c) Require less calcium and phosphorus

Elephant

Whale

Figure 8.4 Skeleton system of elephant and whale

11. Aquatic vertebrates have very small and weak pectoral and pelvic girdles (eg: whales and sharks)

12. A large part of their body weight is supported by the buoyancy of water

13. Buoyancy is the force from water which allows an object to float.

KEDUDUKAN DALAM KELAS (UJIAN 2 OGOS 2011)

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7.3 Application of Frictional force

Frictional force

• Frictional force is defined as force that opposes the motion of an object.
• Frictional force occurs whenever two surfaces are in contact with each other.
• Frictional force is in opposite direction to the moving object and it is parallel to the surface.
• Frictional force has direction and magnitude.

Direction and Magnitude of Frictional Force

• Frictional force has direction and magnitude (value) that can be measured.
• The direction of friction is opposite to the motion of the object.
• Thus, friction can  :                                                                                                                                       

           a) Prevent a stationary object from moving    

                                                                                                              

           b) Slow down and stop a moving object

Diagram 1 : Frictional force always opposes the motion of an object

• The factors that affect the magnitude of frictional force are :

           a) Surface condition. The rougher the surface, the larger the frictional force.

           b) Weight of object. The heavier the object, the larger its frictional force.

Examples showing the existence of force

a) Friction enables a ladder to lean against the wall without slipping.

b) Heat produced by friction lights up the match

c) Friction between soles of shoes and the road surface enables us to walk without slipping

d) Friction between the tyres and the road surface prevents the car form skidding on the road

Advantages of friction

• Enables animals to climb trees.
• Allows brakes to slow down or stop a moving vehicle.
• Enables us to hold objects.
• Produces heat to light up the match.
• Enables us to write on paper.

Disadvantages of friction

• Wastes energy.
• Slows down moving objects.
• Wears out surfaces (og. soles of shoes, machines parts, tyres).
• Produces unnecessary heat that can damage machines.
• Produces unnecessary sound.

Ways to increase friction

• Soles of shoes have rough patterns to prevent slipping while walking.
• Tyres have tread patterns or grooves to prevent vehicles from skidding.
• The rough surface of the steering wheel cover helps the driver in turning the steering wheel.
• Handles of axes, knives and scissors have rough surfaces to ensure a firmer grip on the fools.

Ways of reducing friction

• Using ball bearings

Ball bearing are placed around the axles of wheels of vehicles to reduce friction

• Using wheels

Vehicles and heavy objects such as piano, sewing machine and sofa set are fitted with wheels so that they can moved easily

• Using rollers

Conveyor belts fitted with metal rollers are used to transfer luggage in airports and heavy objects in factories

• Using lubricants such as grease and oil

Oil or grease is applied to the hinges of doors and windows to reduce friction. Engines and machines are lubricated with oil to reduce friction.

• Using a cushion of air

Friction between two surfaces can be reduced by a layer of air between them. The air puck glides easily when it is pushed. Air that comes out of the balloon forms a cushion of air puck and table surface, whereby reducing the friction between them.

The cushion of air between the hovercraft and the water surface enables hovercraft to move faster.