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How Do We Know the Mass of the Earth?

That sounds like a pretty big question, so let’s start back at the beginning. It all began with Newton and his Principia. Well, perhaps a bit earlier, as many ancient scholars had tried their hand at measuring the mass of the Earth (I’m looking at you, Eratosthenes), but no one could get it right, because no one understood the density of the entire planet. When you think about it, we’re tiny creatures living on a huge island in a sea of nothingness, so how can we expect to understand anything about the universe, let alone the mass of our entire home planet?

NEWTON’S PLIGHT

The answer that Newton found to this question was actually quite simple after he came up with this neat little formula:

F=GmM/r^2

where F is the gravitational force,

G is the gravitational constant,

M is the mass of the Earth,

r is the radius of the Earth, and

m is the mass of another object

The only problem with this formula, Newton realized, was that he didn’t know the mass of the Earth, nor the gravitational constant. Essentially, he created the most elegant formula of his age, but was unable to fill in its blanks… that must have been a bummer for poor old Newton.

MASKELYNE AND HUTTON: MOUNTAIN-WEIGHERS, PVT. LTD

This scientific frustration led to his conclusion that the key to calculating those two variables would be measuring the gravitational deflection of an object being exposed to a large enough mass, such as a mountain, along with the mass of the Earth. Of course, that would mean that a scientist would have to know the mass of a mountain. Fortunately, Nivel Maskelyne was up to that task. With the help of mathematician Charles Hutton, Maskelyne decided to weigh the Schiehallion mountain.

Extrapolating data from all the tedious measurements, they measured the mass of the Earth to be approximately 5000 million million tons. They also calculated the gravitational constant and the masses of the Sun, the other planets, and all their moons. They even invented contour lines in the process! The only tiny issue was that they were absolutely, completely, and irrefutably wrong in their calculations. On the bright side, geologists got contour lines as a consolation prize.

Maskelyne and Hutton could not convince 18th century scientists of their data, particularly one scientist named John Michell, who was highly skeptical of the data. He began making his own device to measure the mass of the Earth. Unfortunately, he died before he could use any of his equipment. Nevertheless, Michell ensured that his ingenious contraption was passed on to a brilliant, but highly eccentric, scientist named Henry Cavendish.

THE ADVENTURES OF HENRY CAVENDISH

Cavendish was a very busy man. He had discovered or anticipated a huge range of concepts, including the conservation of energy, Ohm’s Law, Dalton’s Law of Partial Pressures, Richter’s Law of Reciprocal Proportions, and Charles’s Law of Gases – just to name a few. Sadly, Cavendish was too ‘shy’ to ever tell the world of his achievements. Born into a rich family, the man was deathly afraid of human contact. In fact, he used to run away screaming from unannounced fans at his doorstep, mumble a few words only to those who consistently avoided eye contact, and corresponded with his butler through letters. Cavendish actually turned his huge estate into a controlled laboratory where he could carry out his experiments in peace. These peaceful experiments included subjecting himself to increasingly strong jolts of electric current while diligently noting down the levels of agony he experienced.

He did publish the results of one experiment, though.

One fine day, an apparatus gathering dust in the corner of his laboratory caught Cavendish’s eye. Remembering it as being Michell’s, he pulled it out of obscurity and began devoting a great deal of attention to it. Beneath all the weights and counter-weights, pendulums and torsion wires, the apparatus had two 350-pound metal spheres suspended next to two smaller spheres. The idea was to measure the gravitational deflection of the smaller spheres with the larger ones, giving us the elusive gravitational constant that had eluded brilliant men for generations. With this device, it was thought that we could finally calculate the mass of the Earth.

Positioning himself in the adjoining room and using a telescope to peep inside, he carefully observed seventeen delicate measurements over the course of a year. The end result? A profound leap in our understanding of the world. The mass of the Earth was finally measured at 6 billion trillion tons.

Today, we have several state-of-the-art devices to measure the same quantity, but the current estimate of 5.9725 billion trillion tons is only 1% more accurate than Cavendish’s groundbreaking calculation. Two centuries have passed, but we have barely improved on his measurement. Cavendish was truly a legend, even if he was a bit of an oddball!

source: www.scienceabc.com

Why Are Planetary Orbits Elliptical and Not Circular?

HEY GUYS NOW IT'S TIME FOR SOME SPACE STUFF.

For many children, a popular science project consists of making dioramas of the solar system, with painted styrofoam balls for planets and orbital paths made of wire. To this day, when most adults think of the solar system, they imagine a group of concentric rings, with the furthest planets on the largest circular ring and the Sun smack-dab in the center.

While that makes for a neat and tidy project, it isn’t actually correct. The orbits of the planets in our solar system (and the vast majority of planetary objects in space) are actually elliptical, not circular.

However, since orbits are repetitive patterns based on gravity, inertia, and mass, how can they be anything but a perfect circle?

The 4 Types of Potential Planetary Orbits

The basic science behind orbits is that two objects with mass will have a gravitational attraction towards one another, thus affecting their movement through space. This is a basic principle of astronomical physics. We typically see orbits with one large object and one much smaller one, so that the large one appears relatively still, while the smaller one “orbits”.  To understand orbits, you also need to consider the energy that both objects bring into the system, and the effects that will have on the shape of the orbit.

Let’s take our Sun, for example. When an object approaches the Sun, depending on its energy and trajectory, it will follow one of four possible orbital paths:spiral, hyperbolic, elliptical, or circular.

The spiral option means that the object will be drawn in at a steep angle by the Sun’s gravitational pull, perhaps because it is very low in mass or energy. The object will fall into a tight spiral around the Sun, which can hardly even be called an orbit, dropping lower and lower until it impacts the surface. 

The hyperbolic option occurs with objects possessing a great deal of speed or distance from the Sun’s surface. The object will approach, and its path will be bent in towards the Sun, but its speed and distance allow it to continue past the Sun, and not be pulled into a repetitive orbit. After forming a hyperbolic orbital path that resembles a U, it will fly off into space, and will never return, unlike the last two orbital options.

The circular option is what most children imagine the solar system to be, and while some planets closer to the Sun form nearly perfect circles (the Earth is only off by 3 degrees), a truly circular orbit is very hard to achieve. The conditions have to be absolutely perfect, namely that the energy coming into the system creates an orbit with absolutely no eccentricity, which is possible, but very rare.

via GIPHY

The elliptical orbit option is what all the planets in our solar system follow, and it makes sense why this type is far more common than perfect circles. When an object is too small or slow to escape the gravitational pull of the Sun, it falls into a repetitive elliptical orbit that is largely dependent on its original energy and trajectory when it entered the system. The orbit can also be affected by the gravitational effects of other orbiting planetary objects, as well, making it imperfect, eccentric, and highly dependent on other factors.

Physics Prefers Ellipses…

Imagine it this way: a planetary object soars by the Sun at a high speed; at this point, it only has its own velocity that it gained during the explosion when it was first created. As it passes near the sun, a new force i.e. the gravitational force of the sun acts on the object and starts to pull it in its direction. But as it falls towards the sun, a new component gets added; this is the velocity because of acceleration due to gravity. This component, combined with the initial velocity that a planet has, keep it from falling into the sun and give rise to an elliptical orbit.

In short, a planet’s path and speed continue to be effected due to the gravitational force of the sun, and eventually, the planet will be pulled back; that return journey begins at the end of a parabolic path. This parabolic shape, once completed, forms an elliptical orbit.

Inertia and gravity must combine in impressive fashion for any orbit to occur, and given how many other factors can affect the velocity and path of an orbiting object (e.g., other sources of mass/gravity), a circular orbit is just highly unlikely.

However, if you decide to become an astrophysicist, perhaps that can be one of your career goals… finding as many perfect circular orbits as you can!

Why Can Pencil Be Easily Erased Off A Paper, But Ink Can’t?

From the books on our shelves to the newspapers, magazines, and documents in our hands, we interact quite a bit with ink on paper. Obviously, we don’t do this nearly as much as we used to, since the rise of cell phone technology, but there is still something quite nostalgic about the printed word, rather than the digital one.

Pressing ink into paper has been going on for nearly 2,000 years, and it has been one of the most important elements of sharing knowledge and information for cultures around the globe. However, ink is a strangely resilient material, and with a few notable exceptions (like cheaply printed newspapers), the ink always sticks to the page. You’ve read countless ink-pressed pages in your life, but have you ever wondered what keeps the ink on the page?

The Science of Paper and Ink

The majority of paper is manufactured in a similar way at the basic level – an even distribution of fibers (made of cellulose) that have small depressions between them, often called pores. These pores are microscopic in nature, and essentially “suck in” ink through capillary action.

Paper Fiber Super-Zoom (Photo Credit: tks2 / Fotolia)

For those of you who don’t know, capillary action is the unusual ability of liquids to move into narrow spaces against or without the assistance of gravity. This phenomenon is actually seen all over, from the sand getting wet at the beach to the way paint moves up the small tubes and hairs of a paintbrush. This occurs as a result of intermolecular forces that are acting on both the exterior surface and the liquid surface.

A combination of surface tension of the liquid, in this case ink, and the adhesion properties of the paper fibers, causes the ink to move down into the pores of the paper, where it will remain to dry. Papers do come in a range of different “porosity”, and you’ll notice that some glossy papers for photographic printing, have no porosity at all, completely enclosing the fibers and preventing ink from soaking in and drying in the same way. Variations in the porosity affect the amount of time ink takes to dry.

Highly absorbent paper actually takes longer to dry, because as more is absorbed, it becomes harder for oxygen to reach it. Therefore, slightly glossy paper (but still porous) will dry faster because there is more ink on the surface that is being exposed to oxygen and drying.

Why Can’t I Erase a Pen? I Can Definitely Erase Pencils…

Pencils are primarily composed of graphite, and when you draw the pencil across the paper, some graphite particles get stuck on the paper fibers, leaving behind the marks and letters you just wrote. When a traditional rubber eraser is used to eliminate these graphite marks, they are being rubber over the surface to create friction, which heats up the rubber molecules, making them sticky. These sticky molecules then pluck out those graphite particles that are on the very top layers of the paper fibers. Suddenly, poof! No more graphite lines.

The Reason We Use Pencils! (Photo Credit: zimmytws / Fotolia)

However, pens are different, as the dyes used in ink pens is a liquid, and seeps deep into the fibers of the paper. When you try to erase marks from a pen after they have dried, the rubber is unable to separate the intermolecular forces, and you would have to physically scratch down to the level of the dried dyes and eliminate the text that way. For many types of paper, however, which have very high porosity, the ink may bleed nearly all the way through, making it impossible to erase with a traditional erase without destroying the paper itself!

Does the Ink Play a Role?

The type of paper used is not the only reason why ink can be absorbed and dried on a piece of paper; the ink itself also plays a part. There are many different types of ink today, but the primarily used type in printing books and newspapers is carbon black pigment, in addition to various surfactants, resins, waxes, lubricants, and drying agents. This pigment is mixed in with what many call a varnish (or vehicle), which moves the color component to the paper. At that point, the varnish is also responsible for helping the ink harden (or dry).

“Drying Ink” (Photo Credit: Giuseppe Porzani / Fotolia)

This varnish is composed of resins, mineral oil, and vegetable oil, which work in tandem to promote drying. The mineral oils must be absorbed, but the resins and vegetable oils will oxidize when spread out in thin layers; this promotes drying on the surface, even if some of the ink below is not completely hardened. Choosing ink with a well designed mix of drying agents and surfactants keeps ink in place on the paper for years to come, unless it gets wet, of course!

What’s With the Ink On Our Fingers?

Cheaply printed newspaper use high absorbency paper and mineral oil-based inks, which are less expensive. Those types of oils dry much better when the paper is heated, but newspapers are printed extremely quickly – thousands of pages per minute – so there is no time to heat the paper and ensure proper drying before the papers are shipped out to news stands all over the country.

Some of the ink on a freshly printed newspaper will remain on the inner fibers of the paper, but in those great big stacks of newspapers, there isn’t a whole lot of oxygen available to dry the remainder of the ink. Therefore, as you’re flipping through the paper, the skin on your fingers experiences some absorption of the ink (as described at the top of the article, with the capillary effect).

If you don’t mind having slightly smudged fingers, then reading the newspaper is probably still a beloved pastime, but for those who have no tolerance for ink that doesn’t stay where it belongs, perhaps you’d be better off reading your news on your smartphone screen!

source: www.scienceabc.com

Why Do Mics Sometimes Make A Squealing Sound When You Speak Into Them?

In a great fit of inspiration, you took a bold step and signed up for the open-mic competition! The contest has started, and there’s some guy on stage talking about something that makes absolutely no sense to you because you’re too freaked out to pay attention. Then, they announce your name and it’s your turn to randomly pick a topic from a bowl and take the stage.

“Good morning, everyone! Today I…”

SCREEEEEEECCCH! A high-pitched squeal erupts from the mic and fills the auditorium; your heart almost jumps into your mouth. ‘What in the world was that noise?’ you think to yourself as your face begins to flush a deep shade of red.

That was not some stupid prank from a friend to add to your anxiety; instead, it’s a very common and almost equally undesirable phenomenon associated with mics and speakers.

Audio Feedback

Photo Credit: disq/Fotolia

The scenario we imagined above is a typical example of ‘audio feedback’. Also referred to as ‘acoustic feedback’, the Larsen Effect or simply ‘feedback’, audio feedback is that high-pitched squeal you occasionally hear when you speak on a microphone. That ‘squeal’ is a special type of positive feedback (when A produces more of B, which in turn produces even more of A) that occurs due to the presence of a sound loop between an audio output and an audio input.

To put it in simple words, feedback is a high-pitched sound that comes out of speakers when something about the arrangement or the calibration of the audio system is not suitable for the desired setting.

Why Does Audio Feedback Occur?

A typical audio system (like a Public Address system or the audio system used by bands) consists of three essential components: a microphone, a speaker and an amplifier. Wherever all three of these components are present, there it the potential for feedback. The reason is simple; feedback occurs when the microphone picks up the output sound from the speakers and then sends it back to the speakers to re-amplify it, kick-starting an endless loop unless interfered with externally.

To understand it better, let’s have a brief look at how typical audio system works.

When you speak in front of a large audience, you obviously have to be loud enough to be audible to everyone present. Sure, you can shout to be loud enough, but that’s not what I, or anyone else (including your doctor), would recommend.

Therefore, you speak into a microphone (or simply, a mic). The mic transmits your voice to another device, known as an amplifier, which enhances the amplitude of the signals that it received from the mic. These ‘amplified’ signals are then sent to the speakers (audio output), where electrical signals are converted into sound and subsequently discharged to the audience.

However, if the sound discharged from the speakers somehow reaches back to the mic (which ideally shouldn’t happen), the process discussed above kick-starts again, i.e., the mic transmits sound to the amplifier, which then transmits to the speaker, and back to the mic… and then this goes on and on. The result is that you hear a high-pitched squeal, which gets louder and louder (due to the reinforced amplitude as a result of multiple rounds of amplification) until it is corrected.

How Can You Avoid Audio Feedback?

The most important thing you must do to avoid feedback is to distance the mic from the speaker as far as practically possible, and position these devices in a way so that the mic doesn’t catch the sound coming out of the speaker too directly. This is why in public addresses or musical shows, the microphone is usually not set facing the speakers. Instead, the mic is brought out in the front, usually in the middle of the left and right speakers, which are kept at the two forward corners of the stage.

Many times during formal addresses, there is a particularly loud and sharp howl that makes everyone squint their eyes or put their hands around their ears. This is because the speaker in question either speaks too softly or is standing too far away from the mic. Consequently, the sound operator has to increase the ‘volume gain’ (thereby increasing the sensitivity of the mic) of the system to make the orator audible to the audience.

Therefore, it is recommended to hold the mic no more than an inch or two away from one’s mouth, so that the mic doesn’t have to work extra hard to capture the sound of one’s voice.

Not that bad!

 the beatles

Audio feedback is not always a nuisance; in fact, it’s pretty desirable in certain situations. Since the 1960s, electric guitar players have been using this otherwise annoying phenomenon to create incredible distortion effects that add to the overall music quality. Many popular artists and bands (including Canned Heat, the Beatles, the Who, The Smashing Pumpkins and Rage Against the Machine) have used feedback in some form or other in some of their songs.

See? Sometimes things aren’t actually as bad and annoying as they may initially seem!

Why Do LCD Screens Produce Ripples When You Put Your Finger On Them?

To point out a location on a map or identify a person in a group photo to a friend, we invariably end up putting our fingers on the computer/laptop screen. While doing that, have you noticed that sometimes tiny ripples form around your fingers?

If your desktop/laptop screen shows those ‘ripples’ when you press a finger against it, it implies that you have an LCD screen. Note that you won’t notice this sort of ‘ripple effect’ in a CRT monitor or an ‘LED monitor’ (LED monitors have an LCD display that use LED backlighting). However, before we get into this strange predilection of LCD screens, let’s have a quick look and do a quick background check on liquid crystals.

Liquid Crystals

The term ‘liquid crystals’ can be somewhat paradoxical; after all, how can something be solid and liquid at the same time? This thought pops up in our heads because we are so used to the idea of only three states of matter, namely solid, liquid and gas. However, that’s not so; in fact, there are not one or two, butmany other states of matter. (For more information, check out How Many States of Matter Are There?). Liquid crystals are also a state of matter.

The ‘nematic’ phase of liquid crystals

As their name suggests, they share their properties and characteristics with both solids and liquids. It is due to liquid crystals that televisions have transformed from being power-guzzling, beastly machines occupying one entire corner of a room to being light and portable enough to be hung on the wall, consuming only a fraction of what primitive televisions consumed to operate.

The characteristic of liquid crystals that makes them ideal to be used in display screens is that they align themselves when an external electric field is applied to them. To be more technically specific, these liquid crystals are sandwiched between two pieces of polarized glass (also known as ‘substrate’, in technical terms). Light from a fluorescent source falls on the first piece of glass and passes on to the liquid crystals.

Now, these crystals align themselves in a way that allows varying levels of light to pass through and subsequently incident on the second piece of glass. The results of this process are the images that you see on the display screen. Note that liquid crystals don’t emit any light themselves; rather, they control whether light gets through them or not by aligning themselves in various patterns.

Pixels

This term has become so commonplace over the past decade that such instances are not uncommon:

A pixel (representing a ‘picture element’) is the smallest point on an image. The higher the number of pixels, the more information is projected through them, meaning more sharpness and clarity of the image. Each pixel consists of three cells; red, blue and green, i.e., one for each cell. Electric signals ensure that the liquid crystals within each cell bend and align themselves to project the myriad of colors you see projected on the screen.

Why do you see ‘ripples’ when you put your finger on the screen?

Now that you know what liquid crystals are and how they align themselves to show different colors on a screen, let’s go back to the question posed in the title of this article. Under normal conditions, namely when your fingers are clicking away on the mouse rather than moving around on the screen, the alignment of liquid crystals is normal, and everything is alright.

However, the moment you put your finger on the screen (to identify the person standing fourth from the top left corner in the class photo, to your friend), you essentially disturb the alignment of the liquid crystals in those pixels. As a result, you see rainbow-colored ripples forming around the point where your fingers touch the screen, as the misaligned liquid crystals cause cells in the pixels to get confused about what colors they are supposed to display. The good thing, though, is that they return to their normal state as soon as you remove your finger.

We know that there are much more sophisticated ways of pointing things out on a computer monitor (like using the pointer of the mouse); yet somehow we invariably tend to poke at the screen with our fingers instead. This isn’t particularly wise, especially if you do it for long periods of time or with extreme force, as you can do permanent damage to the image quality of your screen! So be careful, and keep your fingers where they belong!

SOURCE: www.scienceabc.com