Newton’s first law is commonly stated as:
An object at rest stays at rest and an object in motion stays in motion.
However, this is missing an important element related to forces. We could expand it by stating:
An object at rest stays at rest and an object in motion stays in motion at a constant speed and direction unless acted upon by an unbalanced force.
By the time Newton came along, the prevailing theory of motion—formulated by Aristotle—was nearly two thousand years old. It stated that if an object is moving, some sort of force is required to keep it moving. Unless that moving thing is being pushed or pulled, it will simply slow down or stop. Right?
This, of course, is not true. In the absence of any forces, no force is required to keep an object moving. An object (such as a ball) tossed in the earth’s atmosphere slows down because of air resistance (a force). An object’s velocity will only remain constant in the absence of any forces or if the forces that act on it cancel each other out, i.e. the net force adds up to zero. This is often referred to as equilibrium. The falling ball will reach a terminal velocity (that stays constant) once the force of air resistance equals the force of gravity.
Hope this help
A contact force is a type of force which act on an object by coming in contact with the object. Examples of contact force that acts through a force field are: applied force, frictional force, air resistance force, tension, spring force, etc.
Examples of forces that act through a force field are gravitational force, electromagnetic force, the weak interaction and the strong interaction.
Answer:
The magnitude of the second charge is
or 
Explanation:
The work done in bringing a charged particle from one point to another in the presence of some electric field is equal to the change in the electric potential energy of the charge in moving from one point to another.
The electric potential energy of some charge
at a point in the electric field of another charge
is given by the product of the amount of charge
and electric potential at that point due to the charge
.

The electric potential at that point is given by

where
is the Coulomb's constant.
Therefore,

Now, We have given two charges
and
, whose value is to be found.
When the two charges are infinitely dar apart, the electric potential energy of the system is given by

When the coordinates of position of the two charges are

The distance between the two charges is given by

The electric potential energy of the charges in this configuration is given by

The change in the electric potential energy of the system is equal to the work done to bring the system from inifinitely far apart position to given configuration.
Therefore,

One atom of silicon can properly be combined in a compound withtwo atoms of oxygen to produce silicon dioxide because silicon is very similar to carbon, as it is in the same group as carbon is in, therefore, it is able to make four bonds.
Moreover, Silicon has 4 valence electrons. In order to form an ionic bond, silicon<span> would have to gain or lose 4 electrons.</span>