A force is a push or a pull acting upon an object. When we talk about different types of physical forces we will use the word exert. 'Exert' means 'put to use' or 'exercise'. (For example, all objects exert gravitational forces.)
All forces exist as a result of the interaction between objects. These interactions happen on a macroscopic level, or between objects that can be seen with the naked eye as well as on a microscopic level, which means between elementary particles of matter. Elementary particles are the smallest structural units (building blocks) of matter. They are very small and can be seen only through a very powerful microscope.
There are many types of physical forces. All objects in the universe are usually affected by several different forces at once. This chapter looks at the type of force called magnetic force.
What is magnetic force?
Magnetic force is a push or a pull exerted by a magnet. Magnetic force results from electrically charged elementary particles called electrons. Electrons are always in motion. The force of attraction between an object and a magnet is called magnetism. A magnetic field consists of imaginary lines of flow coming from electrically charged moving particles. Electric charge is a characteristic of some elementary particles.
A magnet is an object that has a magnetic force. Magnetic force exists around a magnet or electrical field. An electric field is a space surrounding an electric charge. We can say, therefore, that magnetic force is generated electromagnetically.
Permanent magnets are also known as ferro-magnets. Ferrum is Latin for iron. All permanent magnets have north and south poles that are commonly referred to as just N and S. Like all forces, magnetic force is a vector quantity which means it has direction and magnitude.
When two magnets are close to each other, there is a force that attracts their poles together. When two magnets have like poles facing each other, the magnetic force pushes them apart. If you break the magnet, you will not separate its poles but make two magnets with two poles each.
Earth's magnetic field is produced by electric currents in its liquid core. The core is the central portion of the Earth. The outer core is composed mainly of a nickel-iron alloy (a mixture of different metals), while the inner core is almost entirely composed of iron.
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Combination of different physical forces
All objects are affected by several different physical forces at once. The force that is the strongest will define the change of an object. Change might mean a change of shape, position or speed of this object. Now, let's look at an example of a combination of different physical forces, where magnetic force is very strong.
Example: a fridge magnet stuck to the fridge door
Object of study: a fridge magnet
Forces affecting an object: chemical bonding forces, gravitational forces, the force of atmospheric pressure and magnetic force.
Chemical bonding forces
All objects are made of very small structural units, called molecules. Molecules hold on to each other with chemical bonding forces. Solid materials have stronger chemical bonding forces than gases and liquids. Different types of material also have different chemical bonding forces.
Gravitation is a force of attraction between all objects in the universe. All objects in the universe are affected by the forces of gravitation. The larger the object is, the stronger its force of gravitation. On Earth, the largest object is the Earth itself, so all objects are attracted or pulled down towards it. In our example, a fridge magnet does not fall down because it is affected by magnetic force.
All objects on Earth are affected by the force of atmospheric pressure. The force of atmospheric pressure is created by the weight of air. Air is not the name of a chemical element or gas. Air is a non-scientific term for a mixture of many different gases. The atmosphere is a layer of different gases surrounding our planet. Even though air seems weightless, it does have a weight. The Earth's atmosphere is about 500 kilometres deep. That is a lot of air! This air pushes down, with its weight, everything on Earth, creating atmospheric pressure.
Magnets attract materials like iron, nickel and cobalt. A fridge magnet is attracted to the metal door of a fridge by magnetic force. The structure and arrangement of elementary particles called electrons and atoms will determine the way material responds to a magnetic field. Materials which are attracted by a magnet are called ferromagnetic.
The magnetic force of the fridge magnet is the force that keeps this magnet 'stuck' to the fridge door. In our example, magnetic force is stronger than all other forces affecting the fridge magnet.
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