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Making Sense of Electrical, Magnetic and Gravitational Fields

Physics Assignment: Consequences map of electric, gravitational and magnetic fields. This prezi displays the concepts of each topic, the consequences and application and how these fields appear in our everyday life.
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on 13 April 2011

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Transcript of Making Sense of Electrical, Magnetic and Gravitational Fields

Electric Fields Gravitational Fields Magnetics Fields Gravitational, Electric, and Magnetic Fields Gravitational, electric, and magnetic forces act on matter from a distance. These fields share many similar properties. The behaviour of matter in these fields can be described mathematically. Technological systems that involve these fields can have an effect on society and the environment. - Zohaib Shahzad What is a Field?

A field is an area that applies a push or a pull on some object. Physicists often represent fields with field diagrams where the field is represented by lines. Although very unrealistic it does give us a picture of what the field in that area might look like. The thing to realize is the field is actually in three dimensions surrounding the object without visible gaps - Magnetic Field - Earth's
Gravitational
Field - Earth's Magnetic Field - Electric Field Key points

• A charged particle in a uniform electric field moves with uniform acceleration.
• From conservation principles, any changes to a particle’s kinetic energy result from corresponding changes to its electric potential energy (when moving in any electric field and ignoring any gravitational effects).

Technology

An inkjet printer uses charged parallel plates to deflect droplets of ink headed toward the paper. One type of inkjet print head ejects a thin stream of small ink droplets while it is moving back and forth across the paper. Typically, a small nozzle breaks up the stream of ink into droplets 1 x 104 m in diameter at a rate of 150 000 droplets per second and moving at 18 m/s. When the print head passes over an area of the paper that should have no ink on it, the charging electrode is turned on, creating an electric field between the print head and the electrode.

The print head emits a steady flow of ink droplets. Uncharged ink droplets pass straight through the deflection plates to form letters. Charged droplets are deflected into the gutter when the paper is to be blank.

Magnetism A material that generates a magnetic field is known as a magnet. Magnetism is defined as the force produced by charged particles (electrons) of a magnet. In simpler terms, a magnetic substance, for example iron, is attracted by a magnet with the force of magnetism. The force generated can be either attractive or repulsive, depending upon the alignment of the charged particles. What is a magnet ? Law of Magnetic Poles

Opposite magnetic poles attract. Similar magnetic poles repel Since an iron filing experiences a force when placed near a magnet, then, by definition, a magnet is surrounded by a magnetic force field. This field is often detected by its effect on a small test compass (magnetized needle). It is visually depicted by drawing magnetic field lines that show the direction in which the N-pole of the test compass points at all locations in the field. How it Works
1.) Magnetic field lines travel from the north pole to the south pole of a magnet on the outside and the south pole to the north pole on the inside, creating continuous loops.
2.) Magnetic field lines never cross
3.) The strength of the magnetic field is indicated by the density of the field lines. The more closely packed the lines are the stronger the magnetic field

Domain Theory of Magnetism

The domain theory states that inside a magnet there are small regions in which the magnetic alignment of all the atoms are aligned in the same directions
Properties of Magnetic Field Lines
a moving electric charge produces a magnetic field (This was Oersted’s Discovery) a magnetic dipole (kind of like a domain) is created by spinning (moving) electrons
a spinning electron creates a changing electric field that acts as a small current
electrons can either spin up or spin down
if the electrons are unpaired (i.e. by themselves), they create a magnetic dipole
this phenomenon occurs a lot in unpaired d-orbital electrons of the ferromagnetic transition metals
this creates paramagnetic (attracted to magnets) substances
if the electrons are paired, the spin up cancels the spin down and no net magnetic dipole is realized. Therefore the substance is not affected by magnets
paired electrons produce a slightly diamagnetic effect and are very slightly repelled by magnetic fields Here are some main points describing our best understanding of what causes magnetism: Electric and Magnetic Fields eventually form: Electromagnetic Fields Electro-Magnetic Fields Prior to the nineteenth century, electricity and magnetism, although similar in many respects, were generally considered separate phenomena. It was left to an accidental discovery by the Danish physicist Hans Christian Oersted (1777–1851), while teaching at the University of Copenhagen, to reveal a relationship between the two. Observing that a magnetic compass needle was deflected by an electric current flowing through a nearby wire, Christian Oersted formulated the basic principle of electromagnetism:

Principle of Electromagnetism:

Moving electric charges produce a magnetic field. What is Electromagnetism ? - Video introducing electromagnetism Quantifying Magnetic Fields History
The idea of magnetic field lines and magnetic fields was first examined by Michael Faraday and later by James Clerk Maxwell. Both of these English scientists made great discoveries in the field of electromagnetism.
- Michael Faraday Impact on the Environment and Society Environment

Electromagnetic radiation can be classified into ionizing radiation and non-ionizing radiation, based on whether it is capable of ionizing atoms and breaking chemical bonds. Ultraviolet and higher frequencies, such as X-rays or gamma rays are ionizing. These pose their own special hazards such as radiation.

The EM radiations like micro waves, radio waves, x-rays, gamma rays have a very good and great approach in the field of medicine and our daily needs like micro wave ovens-which use micro waves; cell phones-which use radio waves; cancer treatment-which use gamma rays and so on. However so as every situation and problem has another side there are also some negative effects of the EM radiation on the human habitat. For example lets deal with the UV rays which are the harmful rays and the effect is being suffered by us in the present environment.

Since the discovery of X-rays the practical use of ionizing radiation and its damaging effects have been a source of concern for occupational health and radiation protection. This led to the introduction of dose limits and strict controls associated with the use of radiation for civil uses.
Radiation has always been a natural part of our environment. Natural radioactive sources in the soil, water and air contribute to our exposure to ionizing radiation, as well as man-made sources resulting from mining and use of naturally radioactive materials in power generation, nuclear medicine, consumer products, military and industrial applications Health Risks

In the early 1970s electromagnetic fields were linked to the onset of childhood leukemia, and other studies have revealed that electromagnetic fields can cause pacemakers to malfunction as well as other equipment and monitors. Electromagnetic energies have also been linked to other illnesses, cancers, and birth defects in animals, too.
Technology using Electromagnetic Fields A particle accelerator is a device that accelerates subatomic particles to high velocities and maintains them in small, consistent beams. Particle accelerators have many applications in common use and in experimental and theoretical physics research. The Large Hadron Collider, the largest particle accelerator in existence at the time of its construction, was designed to collide particles in the hopes of breaking them apart and discovering the theoretical Higgs-Boson particle. Much smaller accelerators are present in the form of cathode ray tubes in simple television sets Another very useful application of electromagnetism is the "CAT scan machine." This machine is usually used in hospitals to diagnose a disease. As we know that current is present in our body and the stronger the current, the strong is the magnetic field. This scanning technology is able to pick up the magnetic fields, and it can be easily identified where there is a great amount of electrical activity inside the body. In grade 11 university physics we learned about the right hand rule for magnetic currents and fields. Right-Hand Rule for a Straight Conductor

If a conductor is grasped in the right hand, with the thumb pointing in the direction of the current, the curled fingers point in the direction of the magnetic field lines.

When an electric current flows through a long, straight conductor, the resulting magnetic field consists of field lines that are concentric circles, centred on the conductor.
- Thumb points in the direction of current. Fingers curl in the direction of the magnetic field A solenoid is a long conductor wound into a coil of many loops. The magnetic field of a solenoid is the sum of the magnetic fields of all of its loops. The field inside the coil can consequently be very strong.

Right-Hand Rule for a Solenoid

If a solenoid is grasped in the right hand, with the fingers curled in the direction of the electric current, the thumb points in the direction of the magnetic field lines in its core.
- Thumb points in the direction of the magnetic field. Fingers curl in the direction of the current in the coil Right hand rule: Force on a Wire Thumb points in the direction of current. Fingers point in the direction of the external magnetic field. The palm faces in the direction of force that the wire experiences Formula for Magnetic Force Mathematical Example A proton travels in a uniform magnetic field with B = 5.0 T. It is moving at 3.5 x 10^5 m/s. Determine the radius of the circular path it will take. Assume Fm and B are perpendicular. Solution Comparing Fields We have just completed looking at different types of fields. It would be neat to compare their relative strengths using standard measurements. Introduction The exponent differ by 39 Gravity makes thing fall very quickly. For example, if someone were to jump off the CN tower, gravity would pull you down in a matter of seconds. When you hit the ground, it is electrostatic repulsion of the nuclei in your body with that nucleus in the ground that stops you in an instant.

Gravity is a weak force; however it works over great distance and is significant to the motion of celestial bodies because of their great mass.

The electromagnetic force, though strong, will not greatly affect planets. This is due to the small amount of charge on a planet. Most planets are relatively neutral and do not attract or repel other planets. The electromagnetic force is more at home in the world of the very small like atoms, protons and electrons.

Overall, all of this is due to fields like the electric, magnetic and gravitational. An area in space that can apply a force to the appropriate particle Particle Accelerators If we want to look at the world of the very small, like atoms and sub-atomic particles, we use devices called particle accelerators. These are sometimes known as atom smashers. They accelerate particles toward one another and smash them into pieces and observe the pieces that come out. Since particles are can be accelerated by forces, there are only two forces that can be used. Since gravity is the weakest force, the force that would be used by particle accelerators is electromagnetism or magnetism. This force acts at large distances to cause attraction between matter. The larger the mass the stronger the interaction Coulomb's Law
The relationship between the forces acting between two charges through a simulation. You will then solve problems related to forces acting between two or more charges.

The interaction between charged objects is a non-contact force that acts over some distance of separation. Charge, charge and distance. Every electrical interaction involves a force that highlights the importance of these three variables. Whether it is a plastic golf tube attracting paper bits, two like-charged balloons repelling or a charged Styrofoam plate interacting with electrons in a piece of aluminum, there is always two charges and a distance between them as the three critical variables that influence the strength of the interaction. Introduction
The magnitudes of the electrostatic force between two point electric charges are directly proportional to the product of the magnitudes of each charge and inversely proportional to the square of a distance between charges.
Coulomb’s Law States that “the magnitude of the Electrostatics force of interaction between two point charges is directly proportional to the scalar multiplication of the magnitudes of charges and inversely proportional to the square of the distances between them.”

Coulomb's law applies whether the two bodies in question have similar or opposite charges. The only difference is one of sign. If a positive value of F is taken as a force of attraction, then a negative value of F must be a force of repulsion. A coulomb which abbreviated as ‘C’ is the standard unit of charge in the metric system. It was named after the French physicist Charles A. de Coulomb (1736-1806) who formulated the law of electrical force that now carries his name.

By the early 1700s, Sir Isaac Newton's law of gravitational force had been widely accepted by the scientific community, which realized the vast array of problems to which it could be applied. During the period 1760-1780, scientists began to search for a comparable law that would describe the force between two electrically charged bodies. Many assumed that such a law would follow the general lines of the gravitational law, namely that the force would vary directly with the magnitude of the charges and inversely as the distance between them.
Coulomb's Equation In this case, k is known
as Coulomb's constant History - Michael Faraday One charge of 2.0 C is 1.5m away from a –3.0 C charge. Determine the force they exert on each other.

Fe = Force (N)
q = Charge (C)
r = distance between the charges (m)
(Coulomb’s Constant) k = 8.99e9 Nm2/C2

Mathematical Example Solution
Fe=(k q_1 q_2)/r^2
Fe=((8.99*〖10〗^9 )(2.0)(-3.0))/〖1.5〗^2
Fe=-2.4*〖10〗^10 N

The negative sign just means that one charge is positive; the other is negative, so there is an attractive force between them.
Coulomb's Law states:

The magnitude of the electrostatic force between two point electric charges is directly proportional to the product of the magnitudes of each charge and inversely proportional to the square of the distance between the charges

Newton's Law of gravitation states:
Every point mass attracts every other point mass by a force pointing along the line intersecting both points. The force is proportional to the product of the two masses and inversely proportional to the square of the distance between the point masses:

Similarity:
1) Both apply the inverse-square law; is inverselyproportional to square of the distance.
2) Talking about spherical objects i.e. point charge, point mass.

Differences:
1.) One is about large mass; one is about small size huge charges.
2.) Gravitation is only about attraction and no repulsion. Coulomb's force has both attraction and repulsion Similarity between other formulas
Coulomb’s law is an equation describing the electrostatic force between electric charges, primarily electromagnetism.

If you have ever taken off a wool sweater in the dry winter months, or combed you hair while being very dry, you probably experienced the same feeling as the person with the Van de Graff generator. The hair on your head stands up. As you move the sweater or comb away from your hair, what happens? The hair slowly starts to fall. You have discovered one of the fundamental laws of nature: Coulomb's law. Coulomb’s law explains the phenomenon behind static electricity.

Static electricity is the electric charge that gathers on the surfaces of objects, including people, under certain conditions. Static electricity is a common, naturally occurring phenomenon and, in most cases, the charge is so small that it cannot harm humans or animals. It can be dangerous to sensitive electronic components and, in rare cases, even to people
Applications

Society (Everyday Life)
- Michael Faraday - Sir Isaac Newton Electric Fields
What is it?

A machine devised to generate electrostatic charge by means of a vertical endless belt collecting charge from a voltage source and transferring it to a large insulated metal dome, where a high voltage is produced.

How does it work?

The Van de Graff generator woks by collecting and transferring electric charges. Excess charges are collected at the base when a rubber band is pulled across a felt pad. The charges are carried up towards the dome where they are transferred to the person making contact. The charges spread out as far as possible and because all of the charges are the same, the hairs on the person stand up and repel each other. The law of electrostatics states that:

Like charges repel each other, unlike charges attract one another and neutral objects are sometimes attracted to charged objects.
Van de Graff Generator Electric field is defined as the electric force per unit charge. The direction of the field is taken to be the direction of the force it would exert on a positive test charge. The electric field is radially outward from a positive charge and radially in toward a negative point charge

The concept of the electric field was introduced by Michael Faraday. The electrical field force acts between two charges, in the same way that the gravitational field force acts between two masses.

Electric Fields are an electric property associated with each point in space when charge is present in any form. The magnitude and direction of the electric field are expressed by the value of E, called electric field strength or electric field intensity or simply the electric field. Knowledge of the value of the electric field at a point, without any specific knowledge of what produced the field, is all that is needed to determine what will happen to electric charges close to that particular point
What are Electric Fields ? The electric force is an “action-at-a-distance” force, since electric charges attract or repel each other even when not in contact. According to Coulomb’s law, the magnitude of the force between two point charges is given by

Electric forces are the attraction between objects or particles with electric charge. Electric force was described as a non-contact force. Action-at-a-Distance Theory

Action at a distance is the interaction of two objects which are separated in space with no known mediator of the interaction. This term was used most often with early theories of gravity and electromagnetism to describe how an object could know the mass (in the case of gravity) or charge (in electromagnetism) of another distant object.
An electric field is a form of energy which can be created in two ways:

• An electric charge has an electric field around it. This field can create a force
on another electric charge which enters it. This is how a proton attracts an
electron to create an atom.
• A changing magnetic field can create an electric field. Likewise, when an
electric field changes, it creates a magnetic field. This is how radiation is
created. Field theory is a theory that explains interactions between bodies or particles in terms of fields. This theory states that a field of force exists in a region of space when an appropriate object placed at any point in the field experiences a force.

Electric field is the the region in which a force is exerted on an electric charge; the electric force per unit positive charge Field Theory Michael Faraday introduced the concept of an electric field in 1846. Faraday would explain the electric force by saying that a charged object sends out an electric field into space; another charge detects this field when immersed in it and reacts according to its charge. This is not a new concept for us since both the gravitational and the magnetic forces are commonly represented by fields.

Faraday was the first to represent electric fields by drawing lines of force around charges instead of force vectors. Force vectors show the direction and magnitude of the electric force on a small, positive test charge placed at each and every point in the field. For the sake of simplicity, continuous field lines are drawn to show the direction of this force at all points in the field. History of Electric Fields Applications of Electric Fields DNA Electrophoresis

Electric fields are used in a process called electrophoresis to separate molecules. Electrophoresis takes advantage of the fact that many large molecules are charged and will move if placed in an electric field. When placed in a medium under the influence of an electric field, different types of molecules will move at different rates because they have different charges and masses. Eventually, the different types of molecules will separate as they move under the influence of the electric field. The picture displayed to the right shows four columns result from DNA taken from different family members. Electrophoresis generates the separated bands, which act as a fingerprint unique to each person. You can see in the picture displayed to the right that each child (C) shares some similar bands with the mother (M) or father (F), as you would expect. Electrophoresis uses electric fields to separate large charged molecules. The bands of DNA serve as a unique fingerprint for an individual. Related individuals show similarities in their bands
Technology DNA electrophoresis is a method used to sort DNA molecules by length. Pieces of DNA are suspended in a tray of gel and subjected to an electric field, which causes them to migrate toward one end of the tray. The DNA separates out into bands, with the distance from the electrode corresponding to length of the strand. The technique plays a role in identifying genes for diagnosing disease and for other forms of genetic research.

An electrical field is then applied to the gel slab. DNA has a negative electric charge, and is attracted to the positive electrode. The gel resists the DNA as it moves; smaller pieces have an easier time moving through the pores in the gel and so travel further. Given a known gel preparation and electrical application, the length of a segment can be very precisely determined by the distance that it travels. It can then be cut from the gel using a scapel.

Science of Electrophoresis Society Electrophoresis has proved to be an invaluable tool in the analysis of crime scene evidence, especially in the area of DNA fingerprinting. This concept of DNA electrophoresis is conducted by forensic scientists. Video Showing how DNA Electrophoresis works Just like the force due to gravity, the force due to electric charges can act over great distances.

Keep in mind that most forces we deal with in everyday life are “contact forces”… objects touch each other directly in order to exert a force on each other. e.g. tennis racket hits a tennis ball

Then the British scientist Michael Faraday came up with the idea of a “field”.

A field is sometimes defined as a sphere of influence. An object within the field will be affected by it.
Think of how you talk about countries in social studies... large, powerful nations can have an influence on nearby countries. Usually as you get further away from the powerful nation, the influence they have on other countries decreases

Analogy Electric current is the rate of charge flow past a given point in an electric circuit, measured in Coulombs/second which is named Amperes. In most DC electric circuits, it can be assumed that the resistance to current flow is a constant so that the current in the circuit is related to voltage and resistance by Ohm's law. Electric Current Ohm's Law defines the relationships between (P) power, (E) voltage, (I) current, and (R) resistance. One ohm is the resistance value through which one volt will maintain a current of one ampere.

( I ) Current is what flows on a wire or conductor like water flowing down a river. Current flows from negative to positive on the surface of a conductor. Current is measured in (A) amperes or amps.

( E ) Voltage is the difference in electrical potential between two points in a circuit. It's the push or pressure behind current flow through a circuit, and is measured in (V) volts.

( R ) Resistance determines how much current will flow through a component. Resistors are used to control voltage and current levels. A very high resistance allows a small amount of current to flow. A very low resistance allows a large amount of current to flow. Resistance is measured in Ώ ohms.

( P ) Power is the amount of current times the voltage level at a given point measured in wattage or watts
Ohm's Law Electric Field Intensity It was stated that the electric field concept arose in an effort to explain action-at-a-distance forces. All charged objects create an electric field that extends outward into the space that surrounds it. The charge alters that space, causing any other charged object that enters the space to be affected by this field. The strength of the electric field is dependent upon how charged the object creating the field is and upon the distance of separation from the charged objects.
Electric Field Lines A more useful means of visually representing the vector nature of an electric field is through the use of electric field lines of force. Rather than draw countless vector arrows in the space surrounding a source charge, it is perhaps more useful to draw a pattern of several lines that extend between infinity and the source charge. These pattern of lines, sometimes referred to as electric field lines, point in the direction that a positive test charge would accelerate if placed upon the line. As such, the lines are directed away from positively charged source charges and toward negatively charged source charges. To communicate information about the direction of the field, each line must include an arrowhead that points in the appropriate direction. An electric field line pattern could include an infinite number of lines. Because drawing such large quantities of lines tends to decrease the readability of the patterns, the number of lines is usually limited. The presence of a few lines around a charge is typically sufficient to convey the nature of the electric field in the space surrounding the lines. Mathematical Example What is the electric field 0.60 m away from a small sphere with a positive charge of 1.2 x 108 C? Solution Since the electric field is thought of as a quantity that exists independently of whether or not a test charge q is present, then we may define it without referring to the other charge. Therefore, the electric field at any point is defined as the electric force per unit positive charge and is a vector quantity Millikan Oil Drop Experiment An experiment performed by Robert Millikan in 1909 determined the size of the charge on an electron. He also determined that there was a smallest 'unit' charge, or that charge is 'quantized'. He received the Nobel Prize for his work. We're going to explain that experiment here, and show how Millikan was able to determine the size of a charge on a single electron. What Millikan did was to put a charge on a tiny drop of oil, and measure how strong an applied electric field had to be in order to stop the oil drop from falling. Since he was able to work out the mass of the oil drop, and he could calculate the force of gravity on one drop, he could then determine the electric charge that the drop must have. By varying the charge on different drops, he noticed that the charge was always a multiple of -1.6 x 10 -19 C, the charge on a single electron. This meant that it was electrons carrying this unit charge. - Apparatus Applications to Technology An inkjet printer uses charged parallel plates to deflect droplets of ink headed toward the paper. One type of inkjet print head ejects a thin stream of small ink droplets while it is moving back and forth across the paper. Typically, a small nozzle breaks up the stream of ink into droplets 1 x 104 m in diameter at a rate of 150 000 droplets per second and moving at 18 m/s. When the print head passes over an area of the paper that should have no ink on it, the charging electrode is turned on, creating an electric field between the print head and the electrode.

The print head emits a steady flow of ink droplets. Uncharged ink droplets pass straight through the deflection plates to form letters. Charged droplets are deflected into the gutter when the paper is to be blank. Inkjet Printer Fundamental Forces Gravitational Force Electromagnetic Force This force acts at large distances to cause attraction and repulsion between matter. The larger the electric charge the stronger the interaction. Weak Nuclear Force This force acts at extremely small distances to cause attraction and repulsion between matter. This force is responsible for the interaction of sub-nuclear particles. Strong Nuclear Force This force acts at very small distance to cause attraction and repulsion between matter. This force is responsible for the interaction of protons and neutrons in the nucleus. Electric Potential Energy Motion of Charged Particles You can store energy in charges. If you separate two opposite charges, you had to do work in order to separate and have thus stored energy. If you push together two like charges, you had to do work in order to get them closer to one another and have thus stored energy. This means that the electric potential energy can either be positive if dealing with like charges (i.e. repulsion) or negative if dealing with unlike charges (i.e. attraction).

Potential energy can be defined as the capacity for doing work which arises from position or configuration. In the electrical case, a charge will exert a force on any other charge and potential energy arises from any collection of charges. For example, if a positive charge Q is fixed at some point in space, any other positive charge which is brought close to it will experience a repulsive force and will therefore have potential energy. The potential energy of a test charge q in the vicinity of this source charge will be: What is it ? The sign of the electric potential energy becomes important in rigorous problem solving. It is convenient to just ignore the sign and mentally determine if you needed to do work and thus stored energy, or the system did the work and energy was transferred into some other form like kinetic energy. - Electric Potential
Energy Equation Calculate the electric potential a distance of 0.40 m from a spherical point charge of +6.4 x 10-6 C. ( Take V = 0 at infinity.) Mathematical Example Solution Applications to Everyday Life
The concept of electric potential is necessary for an understanding of the human nervous system and how it can transmit information in the form of electric signals throughout the body.

A nerve cell, or neuron, consists of a cell body with short extensions, or dendrites, and also a long stem, or axon, branching out into numerous nerve endings. The dendrites convert external stimuli into electrical signals that travel through the neuron most of the way through the long axon toward the nerve endings. These electrical signals must then cross a synapse (or gap) between the nerve endings and the next cell, whether neuron or muscle cell, in the transmission chain. A nerve consists of a bundle of axons.
Society and Health Electrocardiography measures the electric potential difference between any of the two points shown on the patient. The graphs represent normal and abnormal EKGs, with specific parts of a single beating cycle labelled.

An electrocardiogram is a simple, and painless test that can indicate to your healthcare provider if you have any existing heart problems, or a history of any heart problems.
How it Works Electrical impulses travel through the heart, causing the heart to contract (squeeze).

Through placing electrodes on the surface of your chest, upper abdomen, or back area, the electrical impulses can be recorded by the ECG machine.

The specific pattern of the electrical impulses may show many things, including the electrical activity of the heart. Some scientists spend years working on particular experiments. Robert Millikan is a scientist that spent approximately six years determining a number. To most this would seem to be a waste of time but to the electronics industry this number was of immense importance. This discovery won him a Nobel prize. Introduction Details Gravitational Fields Gravity is a force of attraction that exists between any two masses, any two bodies, any two particles. Gravity is not just the attraction between objects and the Earth. It is an attraction that exists between all objects, everywhere in the universe. Sir Isaac Newton (1642 -- 1727) discovered that a force is required to change the speed or direction of movement of an object.

He also realized that the force called "gravity" must make an apple fall from a tree, or humans and animals live on the surface of our spinning planet without being flung off. Furthermore, he deduced that gravity forces exist between all objects. What is Gravity? Newton's "law" of gravity is a mathematical description of the way bodies are observed to attract one another, based on many scientific experiments and observations. The gravitational equation says that the force of gravity is proportional to the product of the two masses (m1 and m2), and inversely proportional to the square of the distance (r) between their centers of mass. Force field exists in the space surrounding an object in which a force is exerted on objects. Thus, a gravitational field exists in the space surrounding an object in which the force of gravity is exerted on objects. The strength of the gravitational field is directly proportional to the mass of the central body and inversely proportional to the square of the

To understand this relationship, we combine the law of universal gravitation and Newton’s second law of motion,

We have Newtons law of universal gravitation And Newtons second law

states that any two objects exert a gravitational force of attraction on each other. The direction of the force is along the line joining the objects. The magnitude of the force is proportional to the product of the gravitational masses of the objects, and inversely proportional to the square of the distance between them. Newtons law of universal gravitation Mathematical Example Determine the mass of Earth using the magnitude of the gravitational field strength at the surface of the Earth, the distance r between Earth’s surface and its centre (6.38 x 106 m), and the universal gravitation constant. Solution A gravitational field exists in the space surrounding an object in which the force of gravity is exerted on objects.

The magnitude of the gravitational field strength surrounding a planet or other body (assumed to be spherical) is directly proportional to the mass of the central body, and inversely proportional to the square of the distance to the centre of the body.

The law of universal gravitation applies to all bodies in the solar system, from the sun to planets, moons, and artificial satellites Application The gravitational field effects the satelite during launch and orbit. Gravity is (almost) as strong in orbit as on the ground - the reason things appear weightless in orbit is simply that everythign is falling at the same rate. The earth has a magnetic field, conductors (ie. electrical wires) moving through a magnetic field will create an electical current - in certain areas of the earth this effect is stronger and can cause serious problems Space Shuttles Using gravity meters to search for mineral deposits Is a device that measures the strength of a gravitational field at a particular location

Devices used to measure the relative acceleration (g) of gravity Geoid Model
The map is known as a geoid - an imaginary global ocean dictated by gravity in the absence of tides and currents.

Gravity does not exert an equal force everywhere on Earth. Factors such as the rotation of the planet, the effects of mountains and density variations in Earth’s interior mean that this fundamental force is not quite the same all over

Fields
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