Reflections for Term 3 Science Test

It's time to talk about my term test! It was the only term that I was proud of this subject! Why? Normal people only needed to take 2 tests in total for Term 1 and 2, however, due to consistent failing, I was required to take 4 tests, which is 2 term tests and 2 retests. It was nothing to be proud of, but well, today, I'm just going to talk about the Term 3 Science test. It was a pleasant surprise as I did superbly well, scoring 35/40, which was 88%!! WOW!! But well, it would not be possible without consistent studying and memorising of the specific terms. What were tested in the test were lenses, colours of light and ecology. The test was in fact easier than expected. To me, ecology was one of the simplest subject I have ever learnt, perhaps because it was taught to us in primary school. It was as though as we are going back to the basics! But despite learning in primary school, I did realise I have forgotten many many things that was thought there. Ecology had covered 70% of the test, which was the reason I did so well! Hopefully, I will not be complacent after this victory of overcoming my science tests and will eventually do well in EOY!! Oh, but there are some things which I could improve on, which is the common mistake of everyone! Careless mistakes that is...Well, the best way to improve on this is just to, check, CHECK and CHECK AGAIN! That's what I have been lacking, but overall, it was okay I guess.

Why do the planets orbit the sun?

This topic has always been an interest in my life, as it has raised my curiousity on what is pulling the planets to be where it is. Before I have researched on it, I previously thought that it was the gravity in Space that makes its position where it is today. Well, let's take a look if I am right or wrong...

The basic reason why the planets revolve around, or orbit the sun (rotate actually is used to describe their spin, for example, the Earth completes one rotation about its axis every 24 hours, but it completes one revolution around the Sun every 365 days), is that the gravity of the Sun keeps them in their orbits. Just as the Moon orbits the Earth because of the pull of Earth's gravity, the Earth orbits the Sun because of the pull of the Sun's gravity.

Why, then, does it travel in an elliptical orbit around the Sun, rather than just getting pulled in all the way? This happens because the Earth has a velocity in the direction perpendicular to the force of the Sun's pull. If the Sun weren't there, the Earth would travel in a straight line. But the gravity of the Sun alters its course, causing it to travel around the Sun, in a shape very near to a circle. This is a little hard to visualize, so let me give you an example of how to visualize an object in orbit around the Earth, and it's analogous to what happens with the Earth and the Sun.

Imagine Superman is standing on Mt. Everest holding a football. He throws it as hard as he can, which is incredibly hard because he's Superman. Just like if you threw a football, eventually it will fall back down and hit the ground. But because he threw it so hard, it goes past the horizon before it can fall. And because the Earth is curved, it just keeps on going, constantly "falling," but not hitting the ground because the ground curves away before it can. Eventually the football will come around and smack Superman in the back of the head, which of course won't hurt him at all because he's Superman. That is how orbits work, but objects like spaceships and moons are much farther from the Earth than the football that Superman threw. This same situation can be applied to the Earth orbiting the Sun - except now Superman is standing on the Sun (which he can do because he's Superman) and he throws the Earth.

Well, so now we know, it is the gravity of the Sun that pulls the planets together! Hence, I am more or less half-correct :)

How does gravity work?

Every time you jump, you experience gravity. It pulls you back down to the ground. Without gravity, you'd float off into the atmosphere -- along with all of the other matter on Earth.

You see gravity at work any time you drop a book, step on a scale or toss a ball up into the air. It's such a constant presence in our lives, we seldom marvel at the mystery of it -- but even with several well-received theories out there attempting to explain why a book falls to the ground (and at the same rate as a pebble or a couch, at that), they're still just theories. The mystery of gravity's pull is pretty much intact.

Newton's Gravity

In the 1600s, an English physicist and mathematician named Isaac Newton was sitting under an apple tree -- or so the legend tells us. Apparently, an apple fell on his head, and he started wondering why the apple was attracted to the ground in the first place.

Newton publicized his Theory of Universal Gravitation in the 1680s. It basically set forth the idea that gravity was a predictable force that acts on all matter in the universe, and is a function of both mass and distance. The theory states that each particle of matter attracts every other particle (for instance, the particles of "Earth" and the particles of "you") with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between them.

So the farther apart the particles are, and/or the less massive the particles, the less the gravitational force.

The standard formula for the law of gravitation goes:

Gravitational force = (G * m1 * m2) / (d²)

where G is the gravitational constant, m1 and m2 are the masses of the two objects for which you are calculating the force, and d is the distance between the centers of gravity of the two masses.

G has the value of 6.67 x 10E-8 dyne * cm²/gm². So if you put two 1-gram objects 1 centimeter apart from one another, they will attract each other with the force of 6.67 x 10E-8 dyne. A dyne is equal to about 0.001 gram weight, meaning that if you have a dyne of force available, it can lift 0.001 grams in Earth's gravitational field. So 6.67 x 10E-8 dyne is a miniscule force.

When you deal with massive bodies like the Earth, however, which has a mass of 6E+24 kilograms, it adds up to a rather powerful gravitational force. That's why you're not floating around in space right now.

The force of gravity acting on an object is also that object's weight. When you step on a scale, the scale reads how much gravity is acting on your body. The formula to determine weight is:

weight = m * g

where m is an object's mass, and g is the acceleration due to gravity. Acceleration due to gravity on Earth, is 9.8 m/s² -- it never changes, regardless of an object's mass. That's why if you were to drop a pebble, a book and a couch off a roof, they'd hit the ground at the same time.

For hundreds of years, Newton's theory of gravity pretty much stood alone in the scientific community. That changed in the early 1900s.

Einstein's Gravity

Albert Einstein, who won the Nobel Prize in Physics in 1921, contributed an alternate theory of gravity in the early 1900s. It was part of his famous General Theory of Relativity, and it offered a very different explanation from Newton's Law of Universal Gravitation. Einstein didn't believe gravity was a force at all; he said it was a distortion in the shape of space-time, otherwise known as "the fourth dimension".

Basic physics states that if there are no external forces at work, an object will always travel in the straightest possible line. Accordingly, without an external force, two objects travelling along parallel paths will always remain parallel. They will never meet.

But the fact is, they do meet. Particles that start off on parallel paths sometimes end up colliding. Newton's theory says this can occur because of gravity, a force attracting those objects to one another or to a single, third object. Einstein also says this occurs due to gravity -- but in his theory, gravity is not a force. It's a curve in space-time.

According to Einstein, those objects are still travelling along the straightest possible line, but due to a distortion in space-time, the straightest possible line is now along a spherical path. So two objects that were moving along a flat plane are now moving along a spherical plane. And two straight paths along that sphere end in a single point.

Still more-recent theories of gravity express the phenomenon in terms of particles and waves. One view states that particles called gravitons cause objects to be attracted to one another. Gravitons have never actually been observed, though. And neither have gravitational waves, sometimes called gravitational radiation, which supposedly are generated when an object is accelerated by an external force.

(adapted from http://science.howstuffworks.com/environmental/earth/geophysics/question232.htm )

The Working of Bicycle Gears

Bicycles are able to work by the use of gears. Today, I will be talking about the gears that help it easier to ride a bicycle! Now, let's talk about the gears...

Bicycle Gears Basics

• Bicycles have two sets of gears driven by a chain drive. The gears in the front are attached to the pedal axle, and the gears in the back are connected to the rear wheel. Most bikes have several gears of different sizes in both the front and back, and a derailleur, which can move the chain from one gear to another. When a cyclist pedals, the front gear pulls the chain, which in turn pulls the corresponding rear gear, turning the wheel.

  Ratios

  • Every gear has a certain number of teeth proportional to its size. The ratio of the number of teeth on the front gear the cyclist uses to the number of teeth in the rear determines how fast the cyclist needs to pedal. If the front gear and the back gear both have 20 teeth, for example, the ratio is 1 to 1. The rear wheel will turn one time for every time the cyclist turns the pedals. If the front gear has 30 teeth and the rear has 10 teeth, the ratio is 3 to 1. The wheel turns three times for every turn of the pedal.

  Effective Gearing

  • Low gears make it easy to pedal the bike, but hard to go fast. Higher gears allow you to go much faster, but require a lot of leg strength. Many bikers will shift down when climbing up a hill, then shift to a higher gear on a downhill or straightaway. Each biker has an optimum cadence at which his legs produce power most efficiently. Bicycle racers try to find this speed and adjust their gears so they are always moving their legs at the same rate.

    (adapted from http://www.ehow.com/how-does_4701553_bicycles-gears-work.html )

    

Reflections for Trip to Science Centre

A few weeks back, I had been to Science Centre with my family. It was an unique place, where we are able to witness certain knowledge that most people are not able to do so at home. One of my most memorable experience there was the telescope section. It talks roughly about the components needed to make your own telescope. From young, being able to look through a telescope was an amazing thing to do, I was fascinated by the fact that you would be able to see and perhaps study the stars or the moon in space. A brief explanation of the use of telescope would be to make distant objects appear larger, perhaps known as an optical instrument. It tells us that a simple telescope can be made from 2 convex lenses: the objective lens and eyepiece lens. For the objective lens, it collects light from a distant object and brings that light or image to a focus, whereas for the eyepiece lens, it takes the light from the focus and magnifies it. The telescope had became a real interest in my life since that trip, however, after searching for sources of making a telescope-like model on the internet, I just did not have all the things needed for such telescopes. Hence, it defeated my purpose of being able to look at the happenings in space. However, I believe I would not give up just like that, and I swore that when I grow up, not only would I look at space through the telescope, I would want to grow up and get at least 1 chance in my life to go up there in person. It made me grown interest in becoming an astronaut, and my dream is to be able to look at the creation of God when I get my chance to be in space. It would be fantastic to be able to see the entire earth!

Refraction in the Working of the eye

Laws of Refraction

—The incident and refracted rays are on the opposite sides of the normal at the point of incident and all three are in the same plane.

The ratio of the sine of the angle incidence to the sine

of the angle of refraction is a constant for a given pair of media.

i.e. Sin i/Sin r = constant

(The constant is the refractive index of the second medium with respect to the first medium)

The Eye

Important Parts of the Eye and their Functions

—Cornea: The front part of the eye is covered by a transparent spherical membrane called the cornea. Light enters the eye through cornea. The space behind the cornea is filled with a liquid called aqueous humor .

—Iris: Just behind the cornea is a dark coloured muscular diaphragm which has a small circular opening in the middle.

Pupil: Pupil is the small circular opening of iris. The pupil appears black because no light is reflected from it.

*The iris regulates the amount of light entering the eye by adjusting the size of the pupil

How iris regulates the amount of light entering the eye?

When the intensity of light is more or if it is a bright source of light then the iris makes the pupil to contract and as a result the amount of light entering the eye decreases

When the intensity of light is less or if the light is dim then the iris dilates the pupil so that more light can enter the eye

—Eye Lens: The eye lens is a convex lens made of a transparent jelly - like proteinaceous material. The eye lens is hard at the middle and gradually becomes soft towards the outer edges. The eye lens is held in position by ciliary muscles. The ciliary muscles help in changing the curvature and focal length of the eye - lens.

—Blind Spot: It is a spot at which the optic nerve enters the eye and is insensitive to light and hence the name.

Retina: The inner back surface of the eye ball is called retina. It is a semi-transparent membrane which is light sensitive and is equivalent to the screen of a camera. The light sensitive receptors of the retina are called rods and cones. When light falls on these receptors they send electrical signals to the brain through the optic nerve. The space between the retina and eye lens is filled with another fluid called vitreous humor.

Working on an eye

The light coming from an object enters the eye through cornea and pupil.

The eye lens converges these light rays to form a real, inverted and diminished image on the retina.

—The light sensitive cells of the retina gets activated with the incidence of light and generate electric signals.

These electric signals are sent to the brain by the optic nerves and the brain interprets the electrical signals in such away that we see an image which is erect and of the same size as the object.

The Amazing Facts of Thunder and Lightning

Introduction

Lightning is the most spectacular element of a thunderstorm. In fact it is how thunderstorms got their name. But most people would be asking, what does thunder have to do with lightning? Well, lightning causes thunder.

Lightning is a giant spark. A single strike of lightning can heat the air around it to 30,000 degrees Celsius! This extreme heating causes the air to expand at an explosive rate. The expansion creates a shock wave that turns into a booming sound wave, better known as thunder. This explains why it has the name thunderstorm.

Thunder and lightning occur at roughly the same time, although you see the flash of lightning before you hear the thunder. This is because light travels much faster than sound.

Lightning and thunder

The sky is filled with electric charge. In a calm sky, the positive (+) and negative (-) charges are evenly spaced throughout the atmosphere. Therefore, a calm sky has a neutral charge.

Inside a thunderstorm, the electric charge is spread out differently. A thunderstorm is made up of ice crystals and hailstones. The ice crystals have a positive charge, and the hailstones have a negative charge. An updraft pushes the ice crystals to the top of the thunderstorm cloud. At the same time, the hailstones are pushed to the bottom of the thunderstorm by its downdraft. These processes separate the positive and negative charges of the cloud into two levels: the positive charge at the top and the negative charge at the bottom.

During a thunderstorm, the Earth's surface has a positive charge. Because opposites attract, the negative charge at the bottom of the thunder cloud wants to link up with the positive charge of the Earth's surface.

Once the negative charge at the bottom of the cloud gets large enough, a flow of negative charge rushes toward the Earth. This is known as a stepped leader. The positive charges of the Earth are attracted to this stepped leader, so a flow of positive charge moves into the air. When the stepped leader and the positive charge from the earth meet, a strong electric current carries positive charge up into the cloud. This electric current is known as the return stroke and humans can see it as lightning.

Making your own lightning

There are ways for us to make our own lightning, however, don’t expect it to be a huge one, or else it would be too much for you to take. Firstly, lightning is just a bigger form of static electricity. Particles in the cloud rub together to produce static electricity. Lightning occurs when electrons are attracted to protons on the ground or in other clouds. Static electricity is in relation with lightning. Static electricity is formed when an object rubs against another object the electrons move between them. Electrons move from negatively charged objects to positively charged ones. We can create our own static electricity; however, it is beyond our natural abilities to see the “lightning” when the static is created. Light travels too fast hence it is only possible for us to feel the static created. These static we produce are easily produced in indoor areas; this is due to the lack of moisture content of the air, making the atmosphere less conductive. Normally, materials are made of atoms and molecules that are electrically neutral, because they have an equal number of positive charges (protons in the nucleus) and negative charges (electrons in "shells" surrounding the nucleus). The phenomenon of static electricity requires a separation of positive and negative charges. When two materials are in contact, electrons may move from one material to the other, which leaves an excess of positive charge on one material, and an equal negative charge on the other. When the materials are separated they retain this charge imbalance. Charge induction occurs when a negatively charged object repels electrons from the surface of a second object. This creates a region in the second object that is more positively charged. An attractive force is then exerted between the objects. For example, when a balloon is rubbed, the balloon will stick to the wall as an attractive force is exerted by two oppositely charged surfaces, for example the surface of the wall gains an electric charge due to charge induction, as the free electrons at the surface of the wall are repelled by the negative balloon, creating a positive wall surface, which is subsequently attracted to the surface of the balloon. Static electricity is usually caused when certain materials are rubbed against each other, like wool on plastic or the soles of shoes on carpet. The process causes electrons to be pulled from the surface of one material and relocated on the surface of the other material. This is a way of creating your own static electricity which will form some sort of lightning when you gain contact with somebody else.

Another safe and easy way to make lightning requires a cotton or wool blanket. This experiment works best on a dry, cool night. Firstly, turn out all the lights and let your eyes adjust to the darkness. Then, put the blanket behind you and hold your fist out about six inches in front of your face. With your other hand pull the blanket slowly over your head, making sure the blanket brushes over your hair. Also, do not let the blanket touch your fist, arm, or face. If the conditions are right, purple sparks will jump from your fist.

Conclusion

The topic “Lightning and Thunder” is indeed interesting, where both are related. Lightning is formed when the negative charge at the bottom of the cloud gets large enough, and a flow of negative charge rushes toward the Earth. However, thunder is formed due to the lightning. As a single strike of lightning can heat the air around it to 30,000 degrees Celsius, this extreme heating causes the air to expand at an explosive rate. The expansion creates a shock wave that turns into a booming sound wave, known as thunder.