Gravity

This time I am going to talk about Gravity and how it affects us and the Universe.

Have you ever wondered how and why the Earth orbits the Sun or the Moon orbits the Earth? You might say that the Sun's gravity keeps the Earth on track and the Earth's gravity keeps the Moon orbiting the Earth. But shouldn't the gravity of the Sun just pull the Earth towards it instead of having it revolve around it? Well, this does not happen because Space behaves like a fabric.

Anything that has a mass has its own gravity. Yes I have my own gravity and you too. Even tiny dust particles have their own gravity even though you don't notice it. And when anything has gravity, it bends the fabric of Space. Lets say you have a piece of cloth/paper (fabric of Space) and you stretch it so that it's flat but slightly relaxed at the same time. You then put a ball (the Sun) on top of it and notice how the fabric bends inwards.

This is the similar to what happens in space. No, space does not bend like a fabric, but it acts like it does. All objects bend space forming a gravitational cone, with the object being in the middle. The Sun's gravitational cone is huge, it extends out much further than the Solar System.  An object's gravitational cone depends on the mass (and not the size) of the object.

If the gravitational cone is big enough, the object can have a satellite orbiting around it. The Earth is a satellite of the Sun and so are the other planets in the Solar System. The Sun's gravitational cone keeps the planets in orbit.

Let's say that the Sun's gravitational cone is an actual cone and a ball is going around the centre of the cone. If the ball is going too slow, it will spiral inwards and fall into the centre. If it's going too fast, it will spiral outwards and fall off the edge of the cone. If it's going on a steady pace and not too fast or slow, it will maintain a steady orbit around the centre. The moon maintains a steady orbit around the Earth and the Earth maintains a steady orbit around the Sun. If Earth was going too slow, we would have crashed into the Sun by now!

Gravity is also capable of bending light! Albert Einstein first suggested that gravity bends light.To confirm this, a detailed experiment was carried out by Sir Arthur Eddington in 1919 (during a solar eclipse). The results were analysed, and in 1920, it was confirmed that gravity bends light. What happened in this experiment to prove thus? During the solar eclipse Eddington could clearly see the stars, hitherto not seen due to the overwhelming brightness of the Sun. The eclipse blocks this dazzle to some extent making the stars visible. What Eddington saw, however, was interesting: the stars appeared to be a little more closer to the Sun than their normal position. Why? This was because the light of those stars had bend towards the Sun due to the gravitational pull of the Sun. This phenomenon is called the Gravitational lens of the Sun. All star that are big enough to have a gravity that strong have a gravitational lens.

I will soon create a link explaining through a video how this gravitational lens works.

In all, the Universe depends on gravity and it would be impossible for life to survive without it.

Although the Universe depends on it, gravity can also turn into the most dangerous things in the Universe. These dangerous things are called black holes.

I will talk about black holes in my next blog.

e=mc squared

Hi everyone, this is my new blog. In my blogs, I will be talking about physics as you may have guessed from the title, and I hope this will help you.

Many of you know Einstein's most popular equation, e=mc squared, but do you know what it means? Well, let me tell you what it means. E stands for energy, M for mass and C stands for speed of light (which is 300 million metres per second). What this means is that the total amount of energy an object has is its mass multiplied by the speed of light squared. For example, 2 kg of water will have an enery of : 

2 x c squared (300,000,000 x 300,000,000) = 1,800,000,000,000,000,000, Joules

( A Joule equals approximately the energy of a 1kg text book dropped from a height of 1.5 metres)

That's a lot of energy (enough to blow up 4 or 5 cities)!! Now, you might be thinking how could water have so much energy? Well this is the best way to explain :

• Hydrogen is the basic element which makes all other elements. A hydrogen atom consists of a proton and a neutron in the nucleus and an electron orbiting the nucleus. The process of making other elements using hydrogen is called fusion (that fuses two or more hydrogen atoms together). This process happened in the big bang and still happens in stars that are about to die.
• If you slam two hydrogen atoms together, you will create a helium atom which consists of two protons, two nuetrons and two electrons. If you slam three hydrogen atoms together you will create a lithium atom which consists of three protons, nuetrons and electrons each. The more hydrogen atoms you slam together, the more different types of elements you make, until you reach elements like uranium which have more than 90 nuetrons, protons and electrons.
• Now, if you can fuse hydrogen atoms together to form other elements, you can also seperate other elements to make hydrogen (using a process called fission). Note that in the process of fusion or fission, the matter does lose or gain mass.
• Like I said before, all elements are made up of hydrogen, and therefore one can say that an object that weighs n grams is made up of n grams of hydrogen. (I know this sounds a bit weird but lets all stick to this)!!
• As you know, when a hydrogen atom splits, it creates an immense amount of energy (like what happens in an atomic bomb). An atomic bomb contains about 2 party balloons of hydrogen ( imagine this blowing up a whole city)!! This gives you an idea of the amount of energy hydrogen atoms have.
• Using fission, if you completely convert all othere elements of an object into hydrogen, and blow it up (like an atom bomb), you would find out exactly how much energy that object has (you can call this potential energy).

So, how does that 2 kg of water have that much energy? Refer to the first two paragraphs in case the information was too heavy to stay on!!

Well the composition of water is H2O, so if you take out all hydrogen atoms and convert oxygen back into hydrogen and blow it up, you would find out that the water has enough energy to blow up 4 or 5 cities! Be careful though, stand at least at a 200 km radius or you will be evaporated!!

So now I hope you understand the meaning of e=mc squared.

PS: Despite all this, I am still wondering how Einstein came up with c, the speed of light.

Do write back....I will post another blog soon!