My Science School

Back and forth, up and down. What makes a swing fly up in the air?

Most of the time you do the work. You “pump” with your legs and body. Sometimes a friend pushes you. And sometimes the wind pushes the empty swing. But something always has to push it. The swing can’t move by itself.

Any time an object moves, something makes it move. The thing that pushes or pulls it is called a force. Ready to find out how forces make things move?

Forces make things speed up (or accelerate). When a force pushes or pulls the object, the object will move in the direction of the force. The bigger the force, and the lighter the object, the greater the acceleration. It can also make something slow down, speed up or change direction.

Every action has an equal and opposite reaction. When a force acts in one direction it creates an equal force in the opposite direction.

Four wheels, two axles, a box, and a handle. That is all a wagon is. But with a wagon, you can easily carry a couple of friends or even give your dog a ride. When you use a wagon, wheels and axles are helping you. You can see the wheels. They are the round parts that roll over the ground. The axles are the rods that connect each pair of wheels. The wheels and axles turn together.

Putting wheels and axles on something makes it easier to move. It would be hard to pull a wagon without wheels. It would just drag over the ground. But wheels on axles roll along smoothly. Cars, trucks, and buses have wheel-and-axle parts, too.

Every day you are helped by other kinds of wheels - wheels that do not roll. A doorknob is a kind of wheel-and-axle machine. The knob is the wheel! You turn it to make the axle pull back the latch so the door can open.

A pencil sharpener has a wheel and axle, too. The handle is part of a wheel. When you turn the handle, it turns an axle that makes the other parts work.

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Wham! Wham! Wham! It is easy to nail two pieces of wood together. You just knock in nails with a hammer. But fastening two pieces of wood together with a screw is not so easy. The screw has to be turned many times to go into the wood.

A screw has a winding edge called a thread. The thread usually goes from the bottom nearly all the way to the top. When you turn the screw, you wind the thread into the wood.

Turning a screw takes more time than hammering in a nail the same size. But the winding thread of the screw is much longer than the straight sides of the nail. There is more of it to grip and hold the wood. So for some jobs, a screw works better than a nail. It holds things together better than a nail would.

A screw really is an inclined plane that curves around and around. Make a paper screw and see for yourself. Cut a triangle shape as shown from a corner of lightweight card. Mark the square corner with an X.

The long cut edge is an inclined plane. Colour this edge with a crayon or felt-tipped pen. Starting at the straight end, with the X next to the rubber, wind the triangle around a pencil. The coloured edge shows you how the inclined plane winds around the screw to form the threads.

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Be careful! That knife is sharp! Don’t prick yourself with that pin! Working with sharp things means taking special care. But some things have to be sharp to work well. A dull knife or a pin without a point isn’t much help at all.

Sharp things have a special shape that makes work easier. They are really all one kind of machine - a machine called a wedge. The thin, sharp end of a wedge can cut or push into things easily. Then the thicker part of the wedge can push through. Knives, saws, and scissors are wedges for cutting. Pins, nails, and needles are wedges used for pushing into or through things. The point makes it easy for the drawing pin to stick into a notice board, for the nail to push into wood, and for the needle to push through cloth.

Axes and metal wedges are used to push the sharp edge into a log. Then the wider part spreads the wood and makes it split.

Many boats have a wedge-shaped bow, or front end. The bow cuts through the water and makes it easy for the boat to glide along.

Slides and Steps

Is a sloping board without a fulcrum a machine? It is if you use it to do some work. It is a kind of simple machine called an inclined plane. Inclined means sloping, and a plane is a flat surface. So an inclined plane is a flat surface that slopes, like a slide in a playground or a ramp.

An inclined plane makes it easy to move things up and down. When you use an inclined plane, you spread out the amount of work you do. If you lift a heavy box onto a table, you move it only a short distance - straight up. But you are doing all the lifting at once. If you slide the box up an inclined plane, you do the lifting little, by little, so the job is easier.

There are other ways to use inclined planes, too. When you wheel your bike or roll a wheelchair up and down a ramp, you are using an inclined plane.

The kind of inclined plane you use most often may not look like one. A stairway is an inclined plane with steps on it. The steps help keep the plane shorter. Imagine how long the inclined plane would have to be if you flattened out the stairs!

Machines can be any shape and size, but they all have one thing in common: they help people do work. When we think of machines, we usually think of big ones with many parts. These machines do big jobs, such as digging holes, washing clothes, or mowing lawns.

But some machines are small. You cut things out with a small machine - a pair of scissors. You sew with a small machine - a needle. And you tighten a screw with a small machine - a screwdriver. These small machines help you do work, too.

It's built to last you a lifetime - quite literally. But though the human body is the most amazing tool at your disposal, it often needs a helping hand. Tools made from metal, wood, and plastic work like extensions of your body, making you feel stronger and helping you work faster and more efficiently. In science, tools like this are called simple machines. And although you might think there's a big difference between a tiny little wrench and a huge great earthmover, exactly the same physics is at work in both.

To do anything at all—to lift a box, to push a car, to get out of bed, to jump in the air, to brush your teeth—you need to use a pushing or pulling action called a force. If you go around telling people you're strong, what you really mean is that your body can apply a lot of force. You may have watched incredibly strong people on TV pulling trucks or trains with their bare hands, but there's a limit to what even the most muscle-bound human body can do. Simple machines let us go beyond that limit. Simple machines can make us all strong!

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How many times can you lift your best friend higher than your head? How many times can your best friend lift you? It doesn’t sound easy, but it is. When you and your friend are on a seesaw, that’s exactly what you are doing.

The seesaw you and your friend are riding is really a kind of machine called a lever. A lever makes pushing and lifting easy, even when things are heavy and hard to move.

The simplest kind of lever is just a straight stick or board and something to rest it on. Suppose you want to move something heavy - a big rock for example. You can push one end of a strong board under the rock. Then you can rest the middle of the board on a log. This is the resting place, or fulcrum. The end of the board near you sticks up. If you push down on the high end of the board, the other end will move up. The heavy rock will move, too.

Archimedes, an ancient Greek scientist, was the first person to describe how levers work. To prove the power of levers, he built a machine that he used to launch a ship all by himself.

When you ride a seesaw, you and your friend take turns using it as a lever. The middle of the seesaw is the fulcrum. Your weight pushes one end down and lifts your friend up. Then your friend’s weight pushes the other end down and lifts you up.

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Moons — also called natural satellites — come in many shapes, sizes and types. They are generally solid bodies, and few have atmospheres. Most planetary moons probably formed from the discs of gas and dust circulating around planets in the early solar system.

There are hundreds of moons in our solar system — even a few asteroids have been found to have small companion moons. Moons that begin with a letter and a year are considered provisional moons. They will be given a proper name when their discoveries are confirmed by additional observations.

Earth's Moon probably formed when a large body about the size of Mars collided with Earth, ejecting a lot of material from our planet into orbit. Debris from the early Earth and the impacting body accumulated to form the Moon approximately 4.5 billion years ago (the age of the oldest collected lunar rocks). Twelve American astronauts landed on the Moon during NASA's Apollo program from 1969 to 1972, studying the Moon and bringing back rock samples.

 

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The first known interstellar object to visit our solar system, 1I/2017 U1 ‘Oumuamua, was discovered Oct. 19, 2017 by the University of Hawaii’s Pan-STARRS1 telescope, funded by NASA’s Near-Earth Object Observations (NEOO) Program, which finds and tracks asteroids and comets in Earth’s neighborhood.

The first confirmed object from another star to visit our solar system, this interstellar interloper appears to be a rocky, cigar-shaped object with a somewhat reddish hue. The object, named ‘Oumuamua by its discoverers, is up to one-quarter mile (400 meters) long and highly-elongated—perhaps 10 times as long as it is wide. That aspect ratio is greater than that of any asteroid or comet observed in our solar system to date. While its elongated shape is quite surprising, and unlike objects seen in our solar system, it may provide new clues into how other solar systems formed.

The object was officially named 1I/2017 U1 by the International Astronomical Union (IAU), which is responsible for granting official names to bodies in the solar system and beyond. In addition to the technical name, the Pan-STARRS team dubbed it ‘Oumuamua (pronounced oh MOO-uh MOO-uh), which is Hawaiian for “a messenger from afar arriving first.”

 

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The Orion Nebula, the brightest nebula in the sky and occupying an area twice the diameter of the full Moon, can be viewed with the naked eye but was missed by early astronomers.

The Orion Nebula’s position in our galaxy is well-known. If we could view the Milky Way from above, it would appear as a pinwheel with four spiral arms. The galaxy contains hundreds of billions of stars and massive amounts of gas and dust. Our solar system resides in the Orion Spur, which sits between the Perseus and Sagittarius arms, about halfway out from the galactic center.

Our earthbound view is different. On a clear summer night in the Northern Hemisphere, the Milky Way’s glow stretches from Cassiopeia in the northeast to Scorpius in the south. From this vantage point, we’re looking along the galaxy’s rim. Toward Scorpius is the central part of the Milky Way. Rather than seeing a field of blazing stars, our view is obscured by huge clouds of dust and gas.

In the winter, we see the sky opposite the stellar traffic jam found toward the galaxy’s center. The winter Milky Way is there, but you need a dark sky to see it with unaided eyes. The winter sky is the brightest of the seasonal skies — it contains the highest concentration of bright stars — and its most famous representative is Orion.

 

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At the center of our galaxy is a supermassive black hole in the region known as Sagittarius A. It has a mass of about 4 million times that of our Sun.

Almost every galaxy, including our Milky Way, has a supermassive black hole at its heart, with masses of millions to billions of times the mass of the Sun. Astronomers are still studying why the heart of galaxies often hosts a supermassive black hole.

Observations of several stars orbiting Sagittarius A*, particularly star S2, have been used to determine the mass and upper limits on the radius of the object. Based on mass and increasingly precise radius limits, astronomers have concluded that Sagittarius A* is the Milky Way's central supermassive black hole.

Reinhard Genzel and Andrea Ghez were awarded the 2020 Nobel Prize in Physics for their discovery that Sgr A* is a supermassive compact object, for which a black hole is the only currently known explanation.

In 2017, direct radio images were taken of Sagittarius A* and M87* by the Event Horizon Telescope. The Event Horizon Telescope uses interferometry to combine images taken from widely spaced observatories at different places on Earth in order to gain a higher picture resolution. It is hoped the measurements will test Einstein's theory of relativity more rigorously than has previously been done. If discrepancies between the theory of relativity and observations are found, scientists may have identified physical circumstances under which the theory breaks down.

 

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A bolide is an extremely bright meteor, especially one that explodes in the atmosphere. In astronomy, it refers to a fireball about as bright as the full moon, and it is generally considered a synonym for a fireball. In geology, a bolide is a very large impactor.

Many explosions recorded in Earth's atmosphere are likely to be caused by the air bursts that result from meteors exploding as they hit the thicker part of the atmosphere. These types of meteors are also known as fireballs or bolides with the brightest known as superbolides. Before entering Earth's atmosphere, these larger meteors were originally asteroids and comets of a few to several tens of metres in diameter, contrasting with the much smaller and much more common "shooting stars".

The most powerful recorded air burst is the 1908 Tunguska event. Extremely bright fireballs traveling across the sky are often witnessed from a distance, such as the 1947 Sikhote-Alin meteor and the 2013 Chelyabinsk meteor, both in Russia. If the bolide is large enough, fragments may survive such as the Chelyabinsk meteorite. Modern developments in infrasound detection by the Comprehensive Nuclear-Test-Ban Treaty Organization and infrared Defense Support Program satellite technology have increased the likelihood of detecting airbursts.

 

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Ethyl formate is an ester formed when ethanol (an alcohol) reacts with formic acid (a carboxylic acid). Ethyl formate has the characteristic smell of rum and is also partially responsible for the flavor of raspberries. It occurs naturally in the body of ants and in the stingers of bees.

This unlikely discovery was made by astronomers studying interstellar objects for new molecules. They had the IRAM radio telescope trained on Sagittarius B2 – a gas cloud at the centre of the Milky Way galaxy – when they found a chemical called ethyl formate. This is one of the aroma compounds that creates the sweet scents of fruit, wine and flowers, and it smells a lot like rum. It is also the chemical that gives raspberries their distinctive flavour.

Ethyl formate is made from ethanol – a common molecule found in star-forming gas clouds – with formic acid, which is a mix of hydrogen, oxygen and carbon atoms. It’s visible to radio telescopes because ethyl formate molecules absorb the radiation from the stars and re-radiate it at radio wavelengths. Ethyl formate molecules are some of the largest molecules ever found in space and are among the building blocks of amino acids, which are vital for life as we know it.

Even though Sagittarius B2 is extremely dense as far as star-forming regions go, it still only has around 3,000 molecules per cubic centimetre, compared to around 25 million trillion molecules per cubic centimetre in the air that we breathe on Earth. So, even if you could breathe in the nebula, it would sadly be too rarefied to actually smell the rum or taste the raspberries.

 

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Scientists have obtained the first image of a black hole, using Event Horizon Telescope observations of the center of the galaxy M87. The image shows a bright ring formed as light bends in the intense gravity around a black hole that is 6.5 billion times more massive than the Sun. This long-sought image provides the strongest evidence to date for the existence of supermassive black holes and opens a new window onto the study of black holes, their event horizons, and gravity.

The Event Horizon Telescope (EHT) — a planet-scale array of eight ground-based radio telescopes forged through international collaboration — was designed to capture images of a black hole. Today, in coordinated press conferences across the globe, EHT researchers reveal that they have succeeded, unveiling the first direct visual evidence of a supermassive black hole and its shadow.

This breakthrough was announced today in a series of six papers published in a special issue of The Astrophysical Journal Letters. The image reveals the black hole at the center of Messier 87, a massive galaxy in the nearby Virgo galaxy cluster. This black hole resides 55 million light-years from Earth and has a mass 6.5 billion times that of the Sun.

The EHT links telescopes around the globe to form an Earth-sized virtual telescope with unprecedented sensitivity and resolution. The EHT is the result of years of international collaboration, and offers scientists a new way to study the most extreme objects in the Universe predicted by Einstein’s general relativity during the centennial year of the historic experiment that first confirmed the theory.

 

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Neutron stars are the smallest and densest stellar objects, excluding black holes and hypothetical white holes, quark stars, and strange stars. Neutron stars have a radius on the order of 10 kilometres (6.2 mi) and a mass of about 1.4 solar masses.

Neutron stars, with a solid crust (and even oceans and an atmosphere!) are the densest solid object we can observe, reaching a few times the density of an atomic nucleus at their core. A sample of neutron star material the size of a grain of sand would weigh roughly the same as the largest ship ever to sail the seas — more than 500,000 tonnes.

Neutron stars also offer a wealth of extreme behaviour which makes them a compelling target for astrophysicists. For the public, however, they seem to suffer from an image problem, lacking the visual appeal of objects that we can image directly, or the otherworldly weirdness of black holes.

Neutron stars comprise one of the possible evolutionary end-points of high mass stars. Once the core of the star has completely burned to iron, energy production stops and the core rapidly collapses, squeezing electrons and protons together to form neutrons and neutrinos. The neutrinos easily escape the contracting core but the neutrons pack closer together until their density is equivalent to that of an atomic nucleus. At this point, the neutrons occupy the smallest space possible (in a similar fashion to the electrons in a white dwarf) and, if the core is less than about 3 solar masses, they exert a pressure which is capable of supporting a star. For masses larger than this, even the pressure of neutrons cannot support the star against gravity and it collapses into a stellar black hole. A star supported by neutron degeneracy pressure is known as a ‘neutron star’, which may be seen as a pulsar if its magnetic field is favourably aligned with its spin axis.

 

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