question: We know universe is made of 4 forces : electromagnetism, gravity, weak & strong nuclear force. What kind of force is then pushing something with your arms?
comment: Electromagnetic. Basically the atoms in your hands are electromagnetically repelling the atoms in what you're pushing.
passages: Tug of war (astronomy)
  
  The tug of war in astronomy is the ratio of planetary and solar attractions on a natural satellite. The term was coined by Isaac Asimov in "The Magazine of Fantasy and Science Fiction" in 1963.
  
  Section::::Law of universal gravitation.
  
  According to Isaac Newton's law of universal gravitation
  
  In this equation 
  
  The two main attraction forces on a satellite are the attraction of the Sun and the satellite's primary (the planet the satellite orbits). Therefore, the two forces are 
   Forces and Fields
  
  Forces and Fields ":The concept of Action at a Distance in the history of physics" (1961) is a book by Mary B. Hesse, published by Philosophical library. 
  
  Section::::Summary.
  
  "Forces and Fields" has eleven chapters. The first ten chapters consist of 5 or more sections. The eleventh, 2 sections. These chapters are titled The Logical Status of Theories, The Primitive Analogies, Mechanism in Greek Science, The Greek Inheritance, The Corpuscular Philosophy, The Theory of Gravitation, Action at a Distance, The Field Theories, The theory of Relativity, Modern Physics, and The Metaphysical Framework of Physics.
  
  Section::::See also.
   In motor control and robotics, back-EMF often refers most specifically to actually using the voltage generated by a spinning motor to infer the speed of the motor's rotation for use in better controlling the motor in specific ways.
   Section::::Founding members.:Hammersuit Zero-X.
   Researchers have classified the robotic arm by showing its industrial application, medical application, and technology, e.t.c. It has been first introduced in the late 1930s by William Pollard and Harold A. Roseland, where they developed a sprayer that had about five degrees of freedom and an electric control system. Pollard's was called “first position controlling apparatus.” William Pollard never designed or built his arm, but it was a base for other inventors in the future.
   Besides the microtubules, the axoneme contains many proteins and protein complexes necessary for its function. The dynein arms, for example, are motor complexes that produce the force needed for bending. Each dynein arm is anchored to a doublet microtubule; by "walking" along an adjacent microtubule, the dynein motors can cause the microtubules to slide against each other. When this is carried out in a synchronized fashion, with the microtubules on one side of the axoneme being pulled 'down' and those on the other side pulled 'up,' the axoneme as a whole can bend back and forth. This process is responsible for ciliary/flagellar beating, as in the well-known example of the human sperm.
   Pushing on a string
  
  Pushing on a string is a figure of speech for influence that is more effective in moving things in one direction than another – you can "pull," but not "push."
  
  If something is connected to someone by a string, they can move it toward themselves by pulling on the string, but they cannot move it away from themselves by pushing on the string. It is often used in the context of economic policy, specifically the view that "Monetary policy [is] asymmetric; it being easier to stop an expansion than to end a severe contraction."
  
  Section::::History.
   A robotic arm (not robotic hand) is a type of mechanical arm, usually programmable, with similar functions to a human arm; the arm may be the sum total of the mechanism or may be part of a more complex robot. The links of such a manipulator are connected by joints allowing either rotational motion (such as in an articulated robot) or translational (linear) displacement. The links of the manipulator can be considered to form a kinematic chain. The terminus of the kinematic chain of the manipulator is called the end effector and it is analogous to the human hand.
  
  Section::::Types.
   Mechanical arm
  
  A mechanical arm is a machine that mimics the action of a human arm. Mechanical arms are composed of multiple beams connected by hinges powered by actuators. One end of the arm is attached to a firm base while the other has a tool. They can be controlled by humans either directly or over a distance. A computer-controlled mechanical arm is called a robotic arm. However, a robotic arm is just one of many types of different mechanical arms.
   Mechanical arms can be as simple as tweezers or as complex as prosthetic arms. In other words, if a mechanism can grab an object, hold an object, and transfer an object just like a human arm, it can be classified as a mechanical arm.
  
  Recent advancements have been brought about to lead future improvements in the medical field with prosthetics and with the mechanical arm in general. When mechanical engineers build complex mechanical arms, the goal is for the arm to perform a task that ordinary human arms can not complete.
  
  Section::::History.
  
  Section::::History.:Robotic Arms.
   To do so, MOA utilises a so-called Alfvén wave, a physical principle within magnetohydrodynamics that was described first in 1942 by the later Nobel Prize winner Hannes Alfvén and which states that fluctuating magnetic fields can induce density waves in electric conductive media (e.g., plasma, salty water, etc.). These density waves can reach very high velocities and as the particles inside the medium are coupled to them, the particles are as well accelerated to very high velocities, accordingly reaching very high kinetic energies.
  
  Section::::Application areas.
   As constant improvements were being made, the National University of Singapore (NUS) decided to make even further advancements by inventing a mechanical arm that can lift up to 80 times its original weight. Not only did this arm expand its lift strength, but the arm could also extend to five times its original length. These advancements were first introduced in 2012 and car companies can greatly benefit from this new scientific knowledge.
  
  Section::::History.:Surgical Arms.
   Mass driver
  
  A mass driver or electromagnetic catapult is a proposed method of non-rocket spacelaunch which would use a linear motor to accelerate and catapult payloads up to high speeds. All existing and contemplated mass drivers use coils of wire energized by electricity to make electromagnets. Sequential firing of a row of electromagnets accelerates the payload along a path. After leaving the path, the payload continues to move due to momentum. 
   A related question, raised by Ernst Mach, was how rotating bodies know how much to bulge at the equator. This, it seems, requires an action-at-a-distance from distant matter, informing the rotating object about the state of the universe. Einstein coined the term Mach's principle for this question.
   Electromagnetic waves are a type of wave that originate from charged particles, are characterized by varying wavelength and are categorized along the electromagnetic spectrum. Any device that uses electricity will emit electromagnetic radiation due to the magnetic field created by charged particles moving along a medium. For example, radio waves are emitted by electricity moving along a radio transmitter, or even from a satellite.
   Field propulsion
  
  Field propulsion is the concept of spacecraft propulsion where no propellant is necessary but instead momentum of the spacecraft is changed by an interaction of the spacecraft with external force fields, such as gravitational and magnetic fields from stars and planets. It is purely speculative and has not yet been demonstrated to be of practical use, or theoretically valid.
  
  Section::::Types.
  
  Section::::Types.:Practical methods.
   The simplest type of neural circuit is a reflex arc, which begins with a sensory input and ends with a motor output, passing through a sequence of neurons connected in series. This can be shown in the "withdrawal reflex" causing a hand to jerk back after a hot stove is touched. The circuit begins with sensory receptors in the skin that are activated by harmful levels of heat: a special type of molecular structure embedded in the membrane causes heat to change the electrical field across the membrane. If the change in electrical potential is large enough to pass the given threshold, it evokes an action potential, which is transmitted along the axon of the receptor cell, into the spinal cord. There the axon makes excitatory synaptic contacts with other cells, some of which project (send axonal output) to the same region of the spinal cord, others projecting into the brain. One target is a set of spinal interneurons that project to motor neurons controlling the arm muscles. The interneurons excite the motor neurons, and if the excitation is strong enough, some of the motor neurons generate action potentials, which travel down their axons to the point where they make excitatory synaptic contacts with muscle cells. The excitatory signals induce contraction of the muscle cells, which causes the joint angles in the arm to change, pulling the arm away.
   Action at a distance
  
  In physics, action at a distance is the concept that an object can be moved, changed, or otherwise affected without being physically touched (as in mechanical contact) by another object. That is, it is the nonlocal interaction of objects that are separated in space.
  
  This term was used most often in the context of early theories of gravity and electromagnetism to describe how an object responds to the influence of distant objects. For example, Coulomb's law and Newton's law of universal gravitation are such early theories. 
   Arm solution
  
  In applied mathematics as used in the engineering field of robotics, an arm solution is a solution of equations that allow the calculation of the precise design parameters of a robot's arms in such a way as to enable it to make certain movements.
   Section::::Robotics.
  
  The literature on the arm swing is partly created by robotics researchers as the stability in locomotion is a significant challenge especially in humanoid robots. So far although many humanoid robots preserve static equilibrium during walking which does not require arm swing, arm movements has been added to a recent humanoid robot walking in dynamic equilibrium.
  
  The pendulum-like motion of arms is also utilized in passive dynamic walkers, a mechanism that can walk on its own.
  
  Section::::Neuromechanical considerations.
   Manipulator (device)
  
  In robotics a manipulator is a device used to manipulate materials without direct contact. The applications were originally for dealing with radioactive or biohazardous materials, using robotic arms, or they were used in inaccessible places. In more recent developments they have been used in diverse range of applications including welding automation, robotically-assisted surgery and in space. It is an arm-like mechanism that consists of a series of segments, usually sliding or jointed called cross-slides, which grasp and move objects with a number of degrees of freedom.
   When this picture is considered in detail, it is seen that the flux tube must charge up and the surrounding plasma must spin around it. The current into or out of the flux tube must be associated with a force that slows down this spinning. Candidate forces are viscosity, friction with neutrals, and inertial forces associated with plasma flows, either steady or fluctuating. It is not known which force is strongest in practice, and in fact it is generally difficult to find any force that is powerful enough to explain the characteristics actually measured.
   If the object is supported so that it remains at rest, for instance by a cable from which it is hanging, or by a surface underneath, or by a liquid on which it is floating, there is also a support force in upward direction (tension force, normal force, buoyant force, respectively). This support force is an 'equal and opposite' force; we know this not because of Newton's Third Law, but because the object remains at rest, so that the forces must be balanced.
   Section::::Uses.:Spacecraft.
   The electromagnetic force is responsible for practically all phenomena one encounters in daily life above the nuclear scale, with the exception of gravity. Roughly speaking, all the forces involved in interactions between atoms can be explained by the electromagnetic force acting between the electrically charged atomic nuclei and electrons of the atoms. Electromagnetic forces also explain how these particles carry momentum by their movement. This includes the forces we experience in "pushing" or "pulling" ordinary material objects, which result from the intermolecular forces that act between the individual molecules in our bodies and those in the objects. The electromagnetic force is also involved in all forms of chemical phenomena.
  