Derive an expression for gravitational field strength at the surface of a planet, assuming that all its mass is concentrated at its centre. The force between the positive charge of protons and negative charge of electrons is called electric force.
Why don't the oppositely charged protons in the nucleus or electrons surrounding them repel each other and fly apart. There is one underlying principle there that you have met before in a slightly different context. Draw a diagram to show why someones weight on top of Everest is significantly less than at the surface of the Earth.
A physical field is an area in which a force occurs, a gravitational field is therefore a region of space in which an object with mass experiences a gravitational force. When we represent fields, we draw field lines to show the direction of the force acting on a test object.
Any two point masses are attracted to each other with a force that is proportional to each of their masses and inversely proportional to the square of the distance between them. Point masses means that we forget about an object having a size, and consider only its mass acting at a single point (we have come across this idea before, when we considered centre of mass). The inverse square law - this occurs quite a lot physics and is worth going into in more detail.
Thus Newton's law of gravitation implies that the gravitational force falls off according to the inverse square law. Then we introduce the constant of proportionality, the universal gravitational constant, G. If the mass of the earth is 6.0x1024kg and its radius is 6400km work out the gravitational force on a 1kg mass on its surface.
Gravitational field strength at a point in a gravitational field is the force exerted on a unit mass at that point.
Read the details of Cavendish's experiment to weigh the Earth, and then complete the worksheet. An electric field is a region of space in which an object with charge experiences an electric force. Observe the electric field pattern set up between two charged parallel plates using the polar particles of semolena. The force acting between two point charges is directly proportional to each of their charges and inversely proportional to the square of the distance between them. Given a physical significance it would denote the ease with which electric field permeates through space. Electric field strength at a point in an electric field is the force exerted on a unit charge at that point. Observe the movement of a test charge movement in different electric fields, with this applet . Have a go at the simulation of Millikan's Oil Drop experiment to determine the fundamental quantity of charge. Basically all the atoms in the magnet are aligned so the electrons are all orbiting the same way.
With this in mind and knowing that the earth is spinning we can determine the earth's magnetic field, and see that it looks very like that of a simple bar magnet.
Explain why what we call the north pole of the earth is in fact a magnetic south pole (think about what a navigation compass actually is).What force acts on a current carrying conductor in a magnetic field? This equation work well provided that the direction of the current and that of the magnetic field are perpendicular. We can predict the direction and calculate the force acting on a current carrying conductor placed in a magnetic field. This means with some simple manipulation we should also be able to predict the direction and size of forces acting on moving charges in a magnetic field. An important note: When we were using the Fleming's left hand rule to predict the direction of forces, etc, we were considering conventional current. For the record, we know that Earth’s magnetic field has changed its polarity more than once in its lifetime. Just like the Sun reversing its magnetic poles, Earthly switches are just a part of our planet’s schedule. A schematic diagram of Earth's interior and the movement of magnetic north from 1900 to 1996.
Don’t be fooled by those saying a magnetic pole reversal would leave us temporarily without a magnetic field, either. Tammy was a professional astronomy author, President Emeritus of Warren Rupp Observatory and retired Astronomical League Executive Secretary. Earth has settled into a pattern of switching magnetic poles about every 200,00 [sic] to 300,000 years… with a period of twice that long since our last reversal. I find that remarkably odd… is that just a statistical blip and if so, just what are the chances? The Earth’s magnetic field is generated in the interior by various processes which generates current. Actually, the rate of deposition need not be constant–we can date the rocks using radioisotopes.
Why has it been 800,000 years since the last flip if it flips every 200,000 – 300,000 years?
Perhaps the core of our planet is irregular and dynamic, and as the Earth spins it’s naturally trending towards stable gyroscopic motion. Somehow after seeing diagram after diagram of neat concentric perfect circles since a child, I honestly doubt things are that clean.
Biologists are busy uncovering mechanisms that enable them to adjust migrations in general, historically and now. Her output is fantastic and is not surprising that the odd typo creeps in.(Only a proportion appears in UT) Compare with any newspaper!

Tammy and the rest of UT are excellent at what they do, and I have no doubt they put a lot of time and effort into it. Science blogs have very little room for error, and any errors that do happen tend to be noticed by many.
Okay here goes…I find these interjections (Yo!) into the comment stream as annoying as TV commercials and pop up ads. Okay, very interesting and I’m glad someone broached this topic but WHY?!?1 Does the core flip over in its metallic womb?
While the dynamo mechanism is accepted by most, there are AFAIK no detailed models that can predict polar migrations.
The problem seems to be that the core is just large and hot enough to not be amenable to laboratory scale models which could inform computer models.
Any concern of vertical uplifts exposing two more stars in our solar quadrant from a passing star system(8 dwarf sized star chain) theory instead of polar reversal?
If you rotate a bar magnet very very slowly ,then after a few billion years it will reverse its pole positions and we my think of flipping as the effect around is not detected in billion years.
During about the last 20 million years of our formation, Earth has settled into a pattern of switching magnetic poles about every 200,000 to 300,000 years… with a period of twice that long since our last reversal.
Scientists say that Earth has reversed its magnetic field hundreds of times over the last three billion years and have sped up slightly with time.
OK, so if the magnetic field reversals have sped up over time as a trend, why has the last reversal taken place at over double the average interval with only hints a reversal initiation could be imminent?? Enter your email address to subscribe to this blog and receive notifications of new posts by email. Deep within the Earth, a fierce molten core is generating a magnetic field capable of defending our planet against devastating solar winds.
The magnetosphere is a large area around the Earth produced by the planet's magnetic field. By examining pottery from prehistory to modern times, scientists have discovered just how dramatically the field has changed in the last few centuries.Theya€™ve found that Eartha€™s magnetic field is in a permanent state of flux. Life has existed on the Earth for billions of years, during which there have been many reversals.
Electrons have a negative charge, protons have a positive charge and neutrons have a neutral charge. Electric force is much stronger  than the gravitational force, but because most macro sized objects have equal numbers of protons and electrons, we rarely see its effects on a large scale. Atoms are composed of a positively charged nucleus, surrounded by negatively charged electrons.
For example for light eminating from a single source in all directions, its intensity is four times less when you are twice as far away from it. Estimate the gravitational force of attraction between two people sitting side by side on a park bench.
It is simply a constant of proportionality that allows us to use our conventional units for charge and force. It can be replaced with er, relative permittivity when the medium separating two charges isn't free space. Each electron is moving thus you have electricity and because there is electricity there is also magnetism.
We must remember that the movement of negative electrical charge is in the opposite direction to conventional current and account for this when we solve problems involving moving charges. If you have, then chances are very good you’ve also heard this perfectly normal function of our planet could spell disaster. During about the last 20 million years of our formation, Earth has settled into a pattern of switching magnetic poles about every 200,000 to 300,000 years… with a period of twice that long since our last reversal.
Earthly magnetic pole reversal is a normal function of our planet and when it does happen its effects will be spread out over hundreds of thousands of years – not flipped like a pancake. She’s received a vast number of astronomy achievement and observing awards, including the Great Lakes Astronomy Achievement Award, RG Wright Service Award and the first woman astronomer to achieve Comet Hunter's Gold Status.
Or is it thought to have a very specific cause, and if so are there any compelling theories? For some reason the “dynamo” has these flips, which occur episodically or quasi-periodically.
It turns out that radiometric dating finds that the rate of rift spreading is fairly constant.
We’re talking about a magnetic field that can only be modeled with supercomputers due to its enormous complexity. If the speed of the reversal is increasing, then it is possible that it can move much faster then it is moving now.
Maybe because it is so much overdue the reversal will start to happen really fast – like within our lifetime. Consider many of the people who post here are professors, researchers, or scientists themselves, and are therefore more likely to notice such things. It is somewhat affected by orbital changes, but changes from passing stars that would affect the orbit would probably have worse effects on the climate et cetera. Same think is happening with earth, read theory of gravitoethertons which gets focussed at center of earth causing magnetism due to monomagnetic coupling of gravitoethertons. The protective field extends thousands of miles into space and its magnetism affects everything from global communication to animal migration and weather patterns.
If a switch happens, we would be exposed to solar winds capable of punching holes into the ozone layer.
In fact, a recent Danish study believes global warming is directly related to the magnetic field rather than CO2 emissions.The study claimed that the planet is experiencing a natural period of low cloud cover due to fewer cosmic rays entering the atmosphere. Furthermore, the ozone holes would be larger and longer-lived,' said Dr Colin Forsyth from the Mullard Space Science Laboratory at UCL. But historic evidence of its decline has already been found in a surprising source a€“ ancient pottery.Scientists have discovered that ancient pots can act as a magnetic time capsule.

Magnetic north drifts around and every few hundred thousand years the polarity flips so a compass would point south instead of north.
Magnetic north drifts and every few hundred thousand years the polarity flips so a compass would point south instead of north.
Astrophysical satellite are just switched off in this location, but from my perspective, this isna€™t much good if you want to study the Brazilian rainforest.a€™'The very highly charged particles can have a deleterious effect on the satellites and astronauts,' added Dr Mona Kessel, a Magnetosphere discipline scientist at Nasa. Because everything else is made up protons, electrons and neutrons they also have electrical charge. Protons are about 1800 times more massive than electrons, but carry the same amount of charge (only positive). How does this force compare with the gravitational force exerted on them by the Earth, i.e. These samples are perfect fossil records which show us what direction the magnetic field was pointed in as the underwater lava emerged. While our magnetic field goes through weaker and stronger phases, there is simply no evidence to be found anywhere that it has ever disappeared completely. The direction of the Earth’s magnetic field in the past is known from the magnetization fingerprint it leaves behind with molten basalt spreading out from the mid-Atlantic ridge. As I was writing this though, it seems like in that data should also be the density and distribution of matter in the core. At least one spelling, punctuation or sentence structure critique per article now, tsk tsk tsk. They do a very good job about correcting mistakes, and often those mistakes are also found in the source articles and press releases. I think this is a good thing, and I often look at articles specifically to see what these posters have to say.
But this magnetic field, so important to life on Earth, has weakened by 15 per cent over the last 200 years. The impact could be devastating for mankind, knocking out power grids, radically changing Eartha€™s climate and driving up rates of cancer.
The strength of the magnetic field also constantly changes and currently it is showing signs of significant weakening.The Earth magnetic field is mainly generated in the very hot molten core of the planet. If the magnetic field continues to decline, over billions of years, Earth could end up like Mars - a once oceanic world that has become a dry, barren planet incapable of supporting life.WHAT ARE THE DANGERS OF A MAGNETIC FLIP? Scientists however, are quick to point out that while a magnetic flip could cause problems for mankind, the event wona€™t be a catastrophic.
Because a compass works on magnetic fields, its needle directs you to the magnetic pole, measured as either positive or negative. These ancient flows were magnetized in the field’s direction at the time of their creation and exist on either side of the Mid-Atlantic Rift where the North American and European continental plates are moving away from each other.
The reason we have a magnetic field is our solid iron core surrounding by hot, fluid metal. Even if it were weakened, our atmosphere would protect us against incoming particles and we’d have more auroral displays at lower latitudes! The material as it solidifies has its magnetization direction parallel to the Earth’s magnetic field at that time. It is obvious that the grammar patrol here would prefer articulate writing skills as apposed to up to date and informative science news that you so brilliantly and of course, professionally, provide for us viewers.
When pots form, the magnetite minerals align with the Eartha€™s magnetic field, just like compass needles. The markings on the modern compass dial would be incorrect if the polarity of Earth’s magnetic fields were reversed! According to computer modeling, this flow creates electric currents which spawn the magnetic fields.
If the rate of this deposition has been constant then it is possible to time-log past magnetic reversals. Perhaps you should have majored in English and the arts rather than Astronomy and related math and sciences disciplines.
Magnetic reversal or flip is the process by which the North Pole is transformed into the South and vice versa, typically following a considerable reduction in the strength of the magnetic field.
The much sought-after spectacle of an aurora would be visible every night all over the Earth as solar winds hit the atmosphere. Like a witch hunt, many would-be prophets say natural occurrences like this might signal doom… But could their theories be correct? While it’s not possible at this point in time to measure the outer core of our planet directly, we can guess at its movement by the changes in the magnetic field.
Is there any reason to believe the strength of the field actually goes away before it comes back in the south?
However, weakening of the magnetic field does not always result in a reversal.During a reversal, scientists expect to see more complicated field pattern at the Earth's surface, with perhaps more than one North and South Pole at any given time. There remains, however, much work yet to be done in understanding the properties of the deep Earth. One such change has occurred for almost 200 years now… Our northern pole has been shifting even more northward. The overall strength of the field, anywhere on the Earth, may be no more than a tenth of its strength now. The Eartha€™s core is a hostile world where the crushing forces and temperatures, similar to that of the surface of the sun, take our scientific understanding and abilities to the limit.'This isn't some crazy theory that might happen,' said Professor Wild. Since it was first located, the pole has shifted its place by more than 600 miles (1,100 km)!
It would seem that it’s moving almost 40 miles per year now, instead of the 10 miles per year as recorded in the early 20th century.

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