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The gravitational force is surprisingly weak—it is only because gravity is always attractive that we notice it at all. Our weight is the gravitational force due to the entire Earth acting on us. On the very large scale, as in astronomical systems, the gravitational force is the dominant force determining the motions of moons, planets, stars, and galaxies. The gravitational force also affects the nature of space and time. As we shall see later in the study of general relativity, space is curved in the vicinity of very massive bodies, such as the Sun, and time actually slows down near massive bodies.

Electromagnetic forces can be either attractive or repulsive. They are long-range forces, which act over extremely large distances, and they nearly cancel for macroscopic objects. (Remember that it is the net external force that is important.) If they did not cancel, electromagnetic forces would completely overwhelm the gravitational force. The electromagnetic force is a combination of electrical forces (such as those that cause static electricity) and magnetic forces (such as those that affect a compass needle). These two forces were thought to be quite distinct until early in the 19th century, when scientists began to discover that they are different manifestations of the same force. This discovery is a classical case of the unification of forces . Similarly, friction, tension, and all of the other classes of forces we experience directly (except gravity, of course) are due to electromagnetic interactions of atoms and molecules. It is still convenient to consider these forces separately in specific applications, however, because of the ways they manifest themselves.

Concept connections: unifying forces

Attempts to unify the four basic forces are discussed in relation to elementary particles later in this text. By “unify” we mean finding connections between the forces that show that they are different manifestations of a single force. Even if such unification is achieved, the forces will retain their separate characteristics on the macroscopic scale and may be identical only under extreme conditions such as those existing in the early universe.

Physicists are now exploring whether the four basic forces are in some way related. Attempts to unify all forces into one come under the rubric of Grand Unified Theories (GUTs), with which there has been some success in recent years. It is now known that under conditions of extremely high density and temperature, such as existed in the early universe, the electromagnetic and weak nuclear forces are indistinguishable. They can now be considered to be different manifestations of one force, called the electroweak force. So the list of four has been reduced in a sense to only three. Further progress in unifying all forces is proving difficult—especially the inclusion of the gravitational force, which has the special characteristics of affecting the space and time in which the other forces exist.

While the unification of forces will not affect how we discuss forces in this text, it is fascinating that such underlying simplicity exists in the face of the overt complexity of the universe. There is no reason that nature must be simple—it simply is.

Questions & Answers

Write short notes of the following 1.Laws 2.Theories
Khang Reply
what is the meaning of evolved
Ibrahim Reply
To advance or to change from one level to another in the evolution chain
Alexander
Explain why a building made of bricks has smaller entropy than the same bricks in a disorganized pile. Do this by considering the number of ways that each could be formed (the number of microstates in each macrostate).
Thenaj Reply
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Daniel Reply
yeah but just need patient
Musbahu
The closeness of a measurement to the accepted value for a specific physical quantity is known as what ?
Successful Reply
what's the procedure for solving exercise 9.
Woodrow Reply
If you dive into water, you reach greater depths than if you do a belly flop. Explain this difference in depth using the concept of conservation of energy. Explain this difference in depth 
Demeay Reply
A mass of 10kg move with a volocity of 4mß.find it's kinetic energy
Samuel Reply
80m/s²
Angel
KE=1/2mv²
Angel
m= 10
Angel
v=4
Angel
Happy to help
Angel
hi
Dike
What is the unit of force in F.P.S system
Sartaj Reply
f=ma, f=m/s2
MD
lb-ft/s^2
Mary
what is an F.P.S system
Angel
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Pelumi
what is the unit for force
Paul Reply
newtons
Angel
hello
Pelumi
Newton or kg. m/sec^2
Hiba
v=sin(att/s) Prove please as dimension consistent or not
Hashim Reply
v=sin(att/s) Prove please as dimension consistent or not
Hashim
what is physics
Dayyabu Reply
what is physic and what are its branches
Gordon Reply
= Kinematics = Quantum Physics = Dynamics = Statistics = Linear algebra = Calculus (Pre - Calculus, Calculus I Calculus II Calculus III Calculus IV) =Astrophysics And many more...... .....
puvananathan
what is andromeda
Akalador Reply
what is the milky way
Akalador
What's the difference between deceleration and negative acceleration?
Lee Reply
Practice Key Terms 2

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Source:  OpenStax, College physics. OpenStax CNX. Jul 27, 2015 Download for free at http://legacy.cnx.org/content/col11406/1.9
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