# What is a force field in physics

Force field

Jan 06,  · A force field in physics is a map of a force over a particular area of space. This could be a map of the force the charges inside a compass needle . electromagnetic, and other fields of force the aim of finding the most economical basis from which, in principle, theories of all other material processes may be derived. Some of these processes are simple—a single particle moving in a given field of force, for .

When a body exerts an influence into the space around itself, we say that the body creates foece " field " around itself. I tried to id up "field forces" but found nothing related to Physics given that phrase. I will assume you mean "force fields". There are 2 examples in Physics. There are many ways to create an electric field. The simplest example of the body that creates the field would be one with a static electric charge Q.

An electric field is a vector ;hysics and the direction of the field depends on the polarity of the charge. When an electric field exists at a location, if a second body with an electric charge q is placed at that location, the body will experience a force of either attraction or repulsion.

Whether the force is attraction or repulsion depends on whether the polarity of Q and q are the same or opposite. There is only one type of source of a gravity field. A body with mass M will have a field surrounding it. When a gravity field exists in a location, if a body pbysics mass m is placed at that location, the body will experience a force of attraction, never repulsion that we proven. When an gravity field exists at a location, if a second body with mass m is placed at that location, the body will experience a force of attraction.

The following link will take you to a site that helped me with this answer. What are field forces in physics? Steve J. Mar 6, Explanation: I tried to look up "field forces" but found nothing related to Physics given that phrase. The first is Electric field. The second is Gravity field There is js one type of source of a gravity field. Related questions Question cf2dd. What does force mean? What are some examples of phyiscs What is a fielld force?

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Sep 10,  · Definitions in physics are operational, i.e., they describe how to measure the thing being defined. The ship's captain can measure the wind's “field of force” by going to the location of interest and determining both the direction of the wind and the strength with which it is blowing. Mar 05,  · I will assume you mean "force fields". When a body exerts an influence into the space around itself, we say that the body creates a " field " around itself. There are 2 examples in Physics. The first is Electric field. There are many ways to create an electric field. Force Fields Vector field that describes the force that would act on a particle at various positions Electric Field Gravitational Field l ?? nit N C =NC?1 N kg =Nkg?1.

Cutting-edge science readily infiltrates popular culture, though sometimes in garbled form. The Newtonian imagination populated the universe mostly with that nice solid stuff called matter, which was made of little hard balls called atoms. In the early twentieth century, consumers of pulp fiction and popularized science began to hear of a new image of the universe, full of x-rays, N-rays, and Hertzian waves. What they were beginning to soak up through their skins was a drastic revision of Newton's concept of a universe made of chunks of matter which happened to interact via forces.

In the newly emerging picture, the universe was made of force, or, to be more technically accurate, of ripples in universal fields of force. What convinced physicists that they needed this new concept of a field of force? Although we have been dealing mostly with electrical forces, let's start with a magnetic example. In fact the main reason I've delayed a detailed discussion of magnetism for so long is that mathematical calculations of magnetic effects are handled much more easily with the concept of a field of force.

First a little background leading up to our example. Now we get to the relevant example. It is clear that two people separated by a paper-thin wall could use a pair of bar magnets to signal to each other. Each person would feel her own magnet trying to twist around in response to any rotation performed by the other person's magnet.

The practical range of communication would be very short for this setup, but a sensitive electrical apparatus could pick up magnetic signals from much farther away. In fact, this is not so different from what a radio does: the electrons racing up and down the transmitting antenna create forces on the electrons in the distant receiving antenna. Both magnetic and electric forces are involved in real radio signals, but we don't need to worry about that yet.

A question now naturally arises as to whether there is any time delay in this kind of communication via magnetic and electric forces. Newton would have thought not, since he conceived of physics in terms of instantaneous action at a distance. We now know, however, that there is such a time delay. If you make a long-distance phone call that is routed through a communications satellite, you should easily be able to detect a delay of about half a second over the signal's round trip of 50, miles.

In fact, we will soon discuss how light itself is made of electricity and magnetism. If it takes some time for forces to be transmitted through space, then apparently there is some thing that travels through space. The fact that the phenomenon travels outward at the same speed in all directions strongly evokes wave metaphors such as ripples on a pond. The smoking-gun argument for this strange notion of traveling force ripples comes from the fact that they carry energy.

First suppose that the person holding the bar magnet on the right decides to reverse hers, resulting in configuration d. She had to do mechanical work to twist it, and if she releases the magnet, energy will be released as it flips back to c.

She has apparently stored energy by going from c to d. So far everything is easily explained without the concept of a field of force. But now imagine that the two people start in position c and then simultaneously flip their magnets extremely quickly to position e , keeping them lined up with each other the whole time.

Imagine, for the sake of argument, that they can do this so quickly that each magnet is reversed while the force signal from the other is still in transit. For a more realistic example, we'd have to have two radio antennas, not two magnets, but the magnets are easier to visualize. During the flipping, each magnet is still feeling the forces arising from the way the other magnet used to be oriented.

Even though the two magnets stay aligned during the flip, the time delay causes each person to feel resistance as she twists her magnet around. How can this be? Both of them are apparently doing mechanical work, so they must be storing magnetic energy somehow. But in the traditional Newtonian conception of matter interacting via instantaneous forces at a distance, interaction energy arises from the relative positions of objects that are interacting via forces.

If the magnets never changed their orientations relative to each other, how can any magnetic energy have been stored? The only possible answer is that the energy must have gone into the magnetic force ripples crisscrossing the space between the magnets. Fields of force apparently carry energy across space, which is strong evidence that they are real things.

This is perhaps not as radical an idea to us as it was to our ancestors. We are used to the idea that a radio transmitting antenna consumes a great deal of power, and somehow spews it out into the universe. Given that fields of force are real, how do we define, measure, and calculate them? A fruitful metaphor will be the wind patterns experienced by a sailing ship. Wherever the ship goes, it will feel a certain amount of force from the wind, and that force will be in a certain direction.

The weather is ever-changing, of course, but for now let's just imagine steady wind patterns. Definitions in physics are operational, i. Charting all these measurements on a map leads to a depiction of the field of wind force like the one shown in the figure.

Each arrow represents both the wind's strength and its direction at a certain location. Now let's see how these concepts are applied to the fundamental force fields of the universe. We'll start with the gravitational field, which is the easiest to understand. As with the wind patterns, we'll start by imagining gravity as a static field, even though the existence of the tides proves that there are continual changes in the gravity field in our region of space.

When the gravitational field was introduced in chapter 2 , I avoided discussing its direction explicitly, but defining it is easy enough: we simply go to the location of interest and measure the direction of the gravitational force on an object, such as a weight tied to the end of a string. In chapter 2 , I defined the gravitational field in terms of the energy required to raise a unit mass through a unit distance. However, I'm going to give a different definition now, using an approach that will be more easily adapted to electric and magnetic fields.

This approach is based on force rather than energy. We couldn't carry out the energy-based definition without dividing by the mass of the object involved, and the same is true for the force-based definition. For example, gravitational forces are weaker on the moon than on the earth, but we cannot specify the strength of gravity simply by giving a certain number of newtons.

We can get around this problem by defining the strength of the gravitational field as the force acting on an object, divided by the object's mass:. We now have three ways of representing a gravitational field.

The magnitude of the gravitational field near the surface of the earth, for instance, could be written as 9. If we already had two names for it, why invent a third? The main reason is that it prepares us with the right approach for defining other fields.

The most subtle point about all this is that the gravitational field tells us about what forces would be exerted on a test mass by the earth, sun, moon, and the rest of the universe, if we inserted a test mass at the point in question. The field still exists at all the places where we didn't measure it. This expression could be used for the field of any spherically symmetric mass distribution, since the equation we assumed for the gravitational force would apply in any such case.

If we make a sea-of-arrows picture of the gravitational fields surrounding the earth, g , the result is evocative of water going down a drain. For this reason, anything that creates an inward-pointing field around itself is called a sink. The earth is a gravitational sink. Knowledge of the field is interchangeable with knowledge of its sources at least in the case of a static, unchanging field.

If aliens saw the earth's gravitational field pattern they could immediately infer the existence of the planet, and conversely if they knew the mass of the earth they could predict its influence on the surrounding gravitational field. Note how the fields cancel at one point, and how there is no boundary between the interpenetrating fields surrounding the two bodies. A very important fact about all fields of force is that when there is more than one source or sink , the fields add according to the rules of vector addition.

The gravitational field certainly will have this property, since it is defined in terms of the force on a test mass, and forces add like vectors. Superposition is an important characteristics of waves, so the superposition property of fields is consistent with the idea that disturbances can propagate outward as waves in a field.

By how much is this reduced when Jupiter is directly overhead? If we visit Io and land at the point where Jupiter is overhead, we are on the same line as these two centers, so the whole problem can be treated one-dimensionally, and vector addition is just like scalar addition.

Let's use positive numbers for downward fields toward the center of Io and negative for upward ones. You might think that this reduction would create some spectacular effects, and make Io an exciting tourist destination. Actually you would not detect any difference if you flew from one side of Io to the other. This is because your body and Io both experience Jupiter's gravity, so you follow the same orbital curve through the space around Jupiter.

The other half of the detector is in Louisiana. A source that sits still will create a static field pattern, like a steel ball sitting peacefully on a sheet of rubber. A moving source will create a spreading wave pattern in the field, like a bug thrashing on the surface of a pond. Although we have started with the gravitational field as the simplest example of a static field, stars and planets do more stately gliding than thrashing, so gravitational waves are not easy to detect.

Newton's theory of gravity does not describe gravitational waves, but they are predicted by Einstein's general theory of relativity. Taylor and R. Hulse were awarded the Nobel Prize in for giving indirect evidence that Einstein's waves actually exist.

They discovered a pair of exotic, ultra-dense stars called neutron stars orbiting one another very closely, and showed that they were losing orbital energy at the rate predicted by Einstein's theory. Since they are essentially the most sensitive vibration detectors ever made, they are located in quiet rural areas, and signals will be compared between them to make sure that they were not due to passing trucks.

This is a thousand times less than the size of an atomic nucleus! There is only enough funding to keep the detectors operating for a few more years, so the physicists can only hope that during that time, somewhere in the universe, a sufficiently violent cataclysm will occur to make a detectable gravitational wave. More accurately, they want the wave to arrive in our solar system during that time, although it will have been produced millions of years before.

The definition of the electric field is directly analogous to, and has the same motivation as, the definition of the gravitational field:. Charges are what create electric fields.

Unlike gravity, which is always attractive, electricity displays both attraction and repulsion. A positive charge is a source of electric fields, and a negative one is a sink. The most difficult point about the definition of the electric field is that the force on a negative charge is in the opposite direction compared to the field. This follows from the definition, since dividing a vector by a negative number reverses its direction.

It's as though we had some objects that fell upward instead of down. What is the electric field at the point P, which lies at a third corner of the square?

## What is a force field in physics: 3 comments

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