(TEMPLET TUGASAN - VERSI BAHASA MALAYSIA) (MUKA SURAT HADAPAN)

<FACULTY 0F EDUCATION AND LANGUAGE

<JANUARI 2011 >

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<TEACHING SCIENCE FOR LOWER PROMARY III >

NO. MATRIKULASI : <810124055068002>

NO. KAD PENGNEALAN : <810124-05-5068>

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E-MEL : <rusnahabdjalil@gmail.com>

PUSAT PEMBELAJARAN : <IPG TENGKU AMPUAN AFZAN

KUALA LIPIS>

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ARAHAN Jangan menyalin soalan dan arahan tugasan dalam jawapan anda. Sediakan jawapan tugasan anda mengikut susunan KRITERIA PENILAIAN

(ASSESSMENT CRITERIA) seperti tertunjuk dalam RUBRIK. Jika RUBRIK TIDAK dibekalkan, ikut arahan/garispanduan yang ditetapkan oleh Fakulti bagi tugasan kursus berkenaan.

Tugasan anda hendaklah antara 2500 hingga 3000 patah perkataan TIDAK termasuk rujukan.

Taipkan jawapan anda dengan menggunakan saiz fon 12 Times New Roman dan langkau baris 1.5.

Tunjukkan bilangan perkataan di hujung tugasan anda. Jadual dan gambar rajah jika ada, hendaklah menunjukkan tajuk yang wajar. Senaraikan secara berasingan, rujukan/referensi dalam muka surat

APENDIKS.

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1) Race you down: air resistance and terminal velocity.

1.2 INTRODUCTION

In fluid dynamics an object is moving at its terminal velocity if its speed is

constant due to the restraining force exerted by the fluid through which it is moving.

Terminal velocity is the term for the state an object reaches when the force of drag

acting on it is equal to the force of gravity acting on it. When an object reaches its

terminal velocity, it no longer accelerates, remaining at whatever velocity it was already

traveling or else slowing down.

As an object accelerates, the amount of drag exerted on it increases. This means that

more force is necessary to sustain the same level of acceleration. If that external force is

increasing, as in a car or plane, then the object can be accelerated well past its terminal

velocity. If, however, the only force being exerted on it is the force of gravity, then

eventually the drag will become as great as the static force of gravity, and the object will

cease to accelerate

A free-falling object achieves its terminal velocity when the downward force of

gravity (Fg) equals the upward force of drag (Fd). This causes the net force on the object

to be zero, resulting in an acceleration of zero.

As the object accelerates (usually downwards due to gravity), the drag force

acting on the object increases, causing the acceleration to decrease. At a particular speed,

the drag force produced will equal the object's weight (mg). At this point the object

ceases to accelerate altogether and continues falling at a constant speed called terminal

velocity (also called settling velocity). Terminal velocity varies directly with the ratio of

weight to drag. More drag means a lower terminal velocity, while increased weight

means a higher terminal velocity. An object moving downward with greater than terminal

velocity (for example because it was affected by a downward force or it fell from a

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thinner part of the atmosphere or it changed shape) will slow until it reaches terminal

velocity.

The downward force of gravity (Fg) equals the upward force of drag (Fd). The net force on the body is then zero, and the result is that the velocity of the object remains constant.

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1. 2 TERMINAL VELOCITY IN SKYDIVERS

A skydiver reaches terminal velocity when the force of air resistance pushing up

against the skydiver is equal to the force of gravity pushing her downward. At this point,

the skydiver is no longer accelerating, but falling at a constant speed. The terminal

velocity for skydivers varies according to weight and physical position, but it's usually a

very healthy 120 miles an hour.

As an object moves through a fluid, such as a liquid or gas there exists a drag force that

acts to impede the motion. This drag force not only acts in the direction opposite to the

motion but also depends on the square of the speed of the object. The fact that the

drag force increases with speed has an important consequence. Consider a falling body. It

is acted on by gravity and a drag force due to the air. When the body begins to fall the

speed is slow and thus its drag force is also small. The acceleration of the falling body is

g. As the body's speed increases so too does the drag and at some point the speed would

increase tot he point where the drag force would act to cancel out the force due to gravity.

Thus the body no longer accelerates and the speed remains constant.

Different objects would have different terminal speeds. The terminal velocity is not only

dependent on the speed of an object but also the density of the fluid through which the

object moves, the cross sectional area presented by the moving object and a drag

coefficient. The cross sectional area is the area cutting across the object in a plane

perpendicular to the direction of motion. The drag coefficient is a dimensionless constant

and depends on the shape of the object. Thus different objects would have different

terminal velocities depending on their shape and the cross sectional area they present

moving through the medium as well as the acceleration due to gravity.

The magnitude of terminal velocity depends on the weight of the falling body. For a

heavy object, the terminal velocity is generally greater than a light object. This is because

air resistance is proportional to the falling body's velocity squared. For an object to

experience terminal velocity, air resistance must balance weight. An example that shows

this phenomenon was the classic illustration of a rock and a feather being dropped

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simultaneously. In a vacuum with zero air resistance, these two objects will experience

the same acceleration. But on the earth this is not true. Air resistance will equal weight

more quickly for the feather than it would for the rock. Thus the rock would accelerate

longer and experience a terminal velocity greater than the feather.

Another factor that affects terminal velocity is the orientation at which a body falls. If an

object falls with a larger surface area perpendicular to the direction of motion it will

experience a greater force and a smaller terminal velocity. On the other hand, if the object

fell with a smaller surface area perpendicular to the direction of motion, it will experience

a smaller force and a greater terminal velocity.

The terminal velocity for a skydiver was found to be in a range from 53 m/s to 76 m/s.

Four out of five sources stated a value between 53 m/s and 56 m/s. Principles of Physics

stated a value of 76 m/s. This value differed significantly from the others. Then again, the

value is variable since the weight and the orientation of the falling body play significant

roles in determining terminal velocity.

A constant velocity reached by an object falling through a resisting medium and being

acted upon by a constant force. A body falling through the atmosphere under the force of

gravity accelerates until its terminal velocity is reached. It is the velocity at which the

upward drag force is equal to the weight of the falling object. The terminal velocity varies

with the weight and orientation of a falling body. An ability to vary terminal velocity is

very important in sky-diving.

While a rock and a feather fall at exactly the same speed in a vacuum, in our atmosphere

this isn't the case. The feather encounters more air resistance, giving the rock more time

to accelerate, and thus giving it a faster terminal velocity. A skydivers can adjust her

terminal velocity by lowering wind resistance and arching into a dive.

Which brings us to the incredibly important topic of parachutes. As the Physics of

Skydiving tells us, "The increase in surface area reduces the terminal velocity to a much

slower speed. One at which you won't go splat." Most skydivers fall in a spread eagle

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position to maximize their surface area, thus lowering their terminal velocity, thus giving

them more time to fall through the sky.

As his speed increases his air resistance will increase

Eventually the air resistance will be big enough to balance the skydiver’s weight. At this point the forces are balanced so his speed becomes constant- this is called TERMINAL VELOCITY

At the start of his jump the air resistance is zero so he accelerate downwards.

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`

When he opens his parachute the air resistance suddenly increase, causing him to start slowly down.

Because he is slowing down his air resistance will decrease until it balances his weight. The skydiver has now reached a new, lower terminal velocity.

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Conclusion

Terminal velocity,  steady speed achieved by an object freely falling through a gas or

liquid. A typical terminal velocity for a parachutist who delays opening the chute is about

150 miles (240 kilometres) per hour. Raindrops fall at a much lower terminal velocity,

and a mist of tiny oil droplets settles at an exceedingly small terminal velocity. An object

dropped from rest will increase its speed until it reaches terminal velocity; an object

forced to move faster than its terminal velocity will, upon release, slow down to this

constant velocity.

Terminal velocity is achieved, therefore, when the speed of a moving object is no longer

increasing or decreasing; the object’s acceleration (or deceleration) is zero. The force of

air resistance is approximately proportional to the speed of the falling object, so that air

resistance increases for an object that is accelerating, having been dropped from rest until

terminal velocity is reached. At terminal velocity, air resistance equals in magnitude the

weight of the falling object. Because the two are oppositely directed forces, the total force

on the object is zero, and the speed of the object has become constant.

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2) Why Sunset and Sunrise red?

2.1 INTRODUCTION

White light coming from the Sun contains all colors of light from red to blue. The

molecules in Earth's atmosphere do not scatter much of the red light, but they do scatter a

significant amount of blue light. This effect causes the blue sky.

These molecules scattering light also cause the Sun to appear redder than it really is.

When the Sun is high in the sky the amount of reddening is small. However the Sun will

still appear redder from the ground than from space because the atmosphere scatters some

of the blue light.

When the Sun is low in the sky, this effect from Rayleigh scattering is much greater.

Much more of the blue light coming from the Sun is scattered away from the direct path

towards our eyes. Hence the Sun will appear very red when it is low in the sky.

Sunrise is the instant at which the upper edge of the Sun appears above the horizon in the

east. Sunrise should not be confused with dawn, which is the (variously defined) point at

which the sky begins to lighten, some time before the sun itself appears, ending twilight.

Because atmospheric refraction causes the sun to be seen while it is still below the

horizon, both sunrise and sunset are, from one point of view, optical illusions. The sun

also exhibits an optical illusion at sunrise similar to the moon illusion.

The apparent westward revolution of Sun around the earth after rising out of the horizon

is due to the Earth's eastward rotation, a counter-clockwise revolution when viewed from

above the North Pole. This illusion is so convincing that most cultures had mythologies

and religions built around the geocentric model. This same effect can be seen with near-

polar satellites as well.

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The effect can increase when the Sun sets or rises over a large city. Pollution particles

increase the effect by scattering or absorbing more blue light than red light.

Sunrise and sunset are calculated from the leading and trailing edges of the Sun, and not

the center; this slightly increases the duration of "day" relative to "night". The sunrise

equation, however, is based on the center of the sun.

The same thing happens to the Moon. It often appears very red when it is low in the sky

for the same reason.

Sunrise and sunset are calculated from the leading and trailing edges of the Sun, and not

the center; this slightly increases the duration of "day" relative to "night". The sunrise

equation, however, is based on the center of the sun.

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2.2 PHENOMENA EXPLAINATION

Incident solar white light traveling through the Earth's atmosphere is attenuated by

scattering and absorption by air molecules and airborne particles via a combination of

Rayleigh scattering and Mie scattering. At sunset and sunrise, sunlight's path through the

atmosphere is much longer than during the daytime, which creates different colors. At

sunrise and sunset there is more attenuation and light scattering by air molecules that

remove violets, blues and greens, relatively enhancing reds and oranges. Because the

shorter wavelength light of violets, blues and greens scatter more strongly by Rayleigh

Scattering, violets, blues and greens are removed almost completely from the incident

beam, leaving mostly only longer wavelength orange and red hues at sunrise and sunset,

which are further scattered by Mie scattering across the horizon to produce intense reds

and oranges when there are soot, dust, or solid or liquid aerosols in the atmosphere. The

removal of the shorter wavelengths of light is due to Rayleigh scattering by air molecules

and small particles of sizes an order of magnitude smaller that the wavelength of visible

light (typically particles and molecules smaller than 50 nm).

When more molecules are in the atmosphere than normal, say after a major volcanic

eruption, the most spectacular sunrises and sunsets can occur. Dust and water particles

reflect light just like gas molecules can, therefore having more molecules in the air cause

more scattering to occur, causing even less pinks and yellows to reach your eyes. More

oranges and reds reach your eyes in this situation leading to intense sunrises and sunsets.

The sun is actually white when observed without any air between the viewer and the sun,

so, sunlight in outer space contains a mixture of violets, blues, greens, yellows, oranges

and reds. Due to Rayleigh scattering, the sun appears reddish or yellowish when we look

at it from earth, since the longer wavelengths of reds and yellow light are scattered the

least, passing through the air to the viewer, while shorter wavelengths like violet, blue,

and green light are effectively removed from direct sunlight by air molecules' Rayleigh

scattering.

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This schematic shows how the

path of light from the sun changes the color of the light when it reaches your eyes

depending on where you are on the earth (or what time of day it is). At midday when the

light is coming in overhead, the light appears blue. By sunset however, when more of the

suns light passes through a thicker layer of atmosphere, more reds continue on to be seen

by the eye.

Rayleigh scattering in glass: it appears blue from the side but orange light shines through

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2.2.1 RAYLEIGHT SCATTERING

Rayleigh scattering is the elastic scattering of electromagnetic radiation due to the

polarizability of the electron cloud in molecules and particles much smaller than the

wavelength of visible light. Rayleigh scattering intensity is fairly omnidirectional and has

a strong reciprocal 4th-power wavelength dependency and, thus, the shorter wavelengths

of violet and blue light are affected much more than the longer wavelengths of yellow to

red light. During the day, this scattering results in the increasingly intense blue color of

the sky away from the direct line of sight to the Sun, while during sunrise and sunset, the

much longer path length through the atmosphere results in the complete removal of

violet, blue and green light from the incident rays, leaving weak intensities of orange to

red light.

After Rayleigh scattering has removed the violets, blues, and greens, people's viewing of

red and orange colors of sunsets and sunrises is then enhanced by the presence of

particulate matter, dust, soot, water droplets (like clouds), or other aerosols in the

atmosphere, (notably sulfuric acid droplets from volcanic eruptions). Particles much

smaller than the wavelength of the incident light efficiently enhance the blue colors for

off-axis short path lengths through air (resulting in blue skies, since Rayleigh scattering

intensity increases as the sixth power of the particle diameter). Larger particles as

aerosols, however, with sizes comparable to and longer than the wavelength of light,

scatter by mechanisms treated, for spherical shapes, by the Mie theory. Mie scattering is

largely wavelength insensitive. Its spacial distribution is highly preferential in the

forward direction of the incident light being scattered, thus having its largest effect when

an observer views the light in the direction of the rising or setting Sun, rather than

looking in other directions.

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During the daytime, Mie Scattering generally causes a diffuse white halo around the Sun

decreasing the perception of blue color in the direction toward the Sun and it causes

daytime clouds to appear white due to white sunlight. At sunset and sunrise, Mie

scattering off of particles and aerosols across the horizon, then transmits the red and

orange wavelengths that remain after Rayleigh scattering has depleted the blue light. This

explains why sunsets without soot, dust, or aerosols are dull and fairly faint red, while

sunsets and sunrises are brilliantly intense when there are lots of soot, dust, or other

aerosols in the air.

( 2,736 words )

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APENDIKS

1. http://llen.wkipedia.org/wiki/ terminal_velocity.

2. http://hypertextbook.com/facts/Jian Huang.shtml.

3. http://www.wisegeek.com/what_is_terminal Velocity.htm.

4. http://www.britannica.com/EBcheeked/topic/5800/terminal_Velocity.

5.http://www.weather questions.com/why_sunsets_red.

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