----Shadow Wang As we all know, there are four fundamental forces in nature. And we have learned the force: gravity. These forces are gravity, electromagnetic, strong nuclear, and weak nuclear. And in our present Universe they have rather different properties. Firstly, I want to introduce the gravity. The four fundamental forces all play central roles in making the Universe what it is today, but it is gravitation that is most important. At 1687, Newton discovered gravity.According to classical mechanics, between two or more masses (or other forms of energy–momentum) a gravitational potential energy exists. Conservation of energy requires that this gravitational field energy is always negative. Particularly, between any two point masses m and M, there always exists a gravitational force of F = GmM/r^2 where r is the distance between their centers. Gravity exists whenever there is matter. Our bodies are experiencing a gravitational pull with, like, our notebooks (or anything else on the earth) but the effects are so small we can never feel it. However, we can sense the gravitational pull with the Earth (like our weight) due to the cumulative effect of billions of billions of the atoms made up our bodies with those atoms of the Earth. (From paragraph 6 http://sciencepark.etacude.com/particle/forces.php) So it means that the larger body, the stronger the force. But on the scale of individual particles, the force is extremely small, only in the order of times that of the strong force. In physics, gravitational acceleration is the acceleration on an object caused by force of gravitation. Neglecting friction such as air resistance, all small bodies accelerate in a gravitational field at the same rate relative to the center of mass. (From paragraph 6 http://sciencepark.etacude.com/particle/forces.php) This equality is true regardless of the masses or compositions of the bodies. The value of acceleration is close to 9.8m/s on earth. There are lots of applications about gravity in our life. When we throw a stone, the stone is always landing. When a driver stops his car on a slope, the car will keep moving on the road. And the next part is electromagnetic. Electromagnetism is a type of physical interaction that occurs between electrically charged particles. The electromagnetic force usually manifests as electromagnetic fields, such as electric fields, magnetic fields and light. Electromagnetic field affects the behavior of charged objects in the vicinity of the field. The electromagnetic field extends indefinitely throughout space and describes the electromagnetic interaction. (From paragraph 1 http://en.wikipedia.org/wiki/Electromagnetism) And Michael Faraday is discoverer on 1831. The electromagnetic force plays a major role in determining the internal properties of most objects encountered in daily life. Ordinary matter takes its form as a result of intermolecular forces between individual molecules in matter. Electrons are bound by electromagnetic wave mechanics into orbitals around atomic nuclei to form atoms, which are the building blocks of molecules. This governs the processes involved in chemistry, which arise from interactions between the electrons of neighboring atoms, which are in turn determined by the interaction between electromagnetic force and the momentum of the electrons.
(From paragraph 3 http://en.wikipedia.org/wiki/Electromagnetism) The discovery electricity and magnetism are two important achievements in 19th century physics. Scientists now know that the field surrounding a permanent magnet is the same as the field surrounding a wire through which an electric current is flowing. There are some application for electricity. Like the touchscreen, Internet and WIFI. And the third one is strong nuclear force. As the name like, it is the strongest force in these four force. His job is holding together the subatomic particles of