## Angular momentum

Angular momentum The quantity of the rotational motion, which is identical to mass (m) in the linear motion, is the moment of inertia (I). The quantity of the rotational motion, which is identical to the velocity (v) in the linear motion, is the angular velocity (ω). Thus, the rotating object has angular momentum that can … Read more

## Moment of inertia

### 1. Moment of inertia of the particle

Review a rotating particle. The particle with mass m is given the force F so that the particle rotates about the axis O. The particle is r apart from the axis of rotation. First, the particle is in rest (v = 0). After moved by the force of F, the particles move with a certain speed so that the particles have tangential acceleration. The relationship between force (F), mass (m), and the tangential acceleration of particles are expressed by equation 3:

## Electric current

### Definition of Electric current

In a conductor such as copper, there are electrons that move randomly at high speed freely but not escape from the metal. Electrons that can move freely are called free electrons. Although the electrons move freely in all directions, there is no total flow of electrons in a particular direction. This condition occurs when there is no potential difference between the two ends of the copper wire.

When the wire is connected to an electrical source, a potential difference arises between the two ends of the copper wire, so that an electric field appears within the copper wire. The existence of an electric field causes free electrons to experience the electric force F = q E = e E, where F = electric force, e = electron charge, E = electric field. This electric force causes all the electrons that are moving freely to accelerate together, which is the same direction as the electric force.

## Parabolic motion Work and kinetic energy Linear momentum Linear and angular motion Problems and Solutions

### 5 Parabolic motion Work and kinetic energy Linear momentum Linear and angular motion Problems and Solutions

1. A ball is thrown from the top of a building with an initial speed of 8 m/s at an angle of 20o below the horizontal. The ball hits the ground 3 seconds later.

a) How far from the bottom of building the ball touches the ground

b) How high is the ball thrown from the place

c) How long the ball reaches a height of 10 m from the place of throwing

## Definition of capacitor

### Article about the Definition of capacitor

The definition of capacitor is a device that stores electrical charge and electrical potential energy. The simple capacitor consists of two-conductor plates or sheets that are placed close together but do not touch each other and are separated by an insulator or a vacuum. Conductors are materials that can conduct electric current such as metals, while insulators are materials that cannot conduct electric current such as plastic.

At first, the two conductors are not electrically charged or electrically neutral. In order for one conductor to be positively charged and the other conductor to be negatively charged, then there must be a transfer of electrons from one conductor to another. The electrons are on the surface of the atom, so they are easy to move. After the electron has moved from one conductor to another, one of the conductors has an excess of electrons (lack of protons)

so that it becomes negatively charged, while the other conductor has an electron deficiency (excess proton) so that it becomes positively charged. A detailed description of the process of charging electric charges on capacitors is reviewed on the topic of storing electrical energy in capacitors.

## Electric potential

### Definition of the electric potential

Electric potential is defined as the electric potential energy per unit charge. Suppose that when it is at point a, the charge q has the electric potential energy equal to EPa, then the electric potential at point a is formulated as follows:

V = electric potential, EP = electric potential energy, q = electric charge

V is not only at point a but also at all points in the electric field. Point a is used as an example. As will be explained later, the V does not depend on the charge q.

## Electric potential energy

### Article about the Electric potential energy

Before studying this topic, first understand work, the conservative forces, the relationship between the conservative forces with potential energy, the electric forces and the electric field.

### Electric force is the conservative forces

In addition to the gravitational force and spring force, the other example of the conservative force is the electric force. To better understand why the electric force is called the conservative force, understand the following explanation.

## Determining the electric field using Gauss law

### Article about Determining the electric field using Gauss law

Electric field by a single point charge

To calculate the electric field produced by a single positive charge, the first step is to select the spherical Gauss surface with radius r where the center of the sphere is at the single charge. The surface area of the ball is 4πr2.

The electric field coming out of the center of the sphere penetrates perpendicular to the surface of the sphere so that the formula of electric flux is Φ = E A. The formula of the Gauss’s law is Φ = Q/εo

## Gauss law

Regarding Coulomb’s law, the force between electric charges has been studied. In a review of the electric field, another form of Coulomb’s law has been discussed, which is expressed by the equation F = q E,

where F is the electric force, q is the electric charge and E is the electric field. It can be said that Coulomb’s law is a law of physics that explains the relationship between the electric charge (q) and the electric field (E).

Gauss’s law is another physics law that explains the relationship between the electric charges and the electric fields. Gauss’s law was formulated by Carl Friedrich Gauss (1777-1855), a German theoretical physicist and mathematician.