## Uniform linear motion

### Definition of the uniform linear motion

An object experiences uniform linear motion if the velocity of the object is constant. Velocity includes the magnitude and direction of velocity. Direction of velocity = direction of displacement = direction of movement. The direction of the velocity of a constant object = the direction of motion of a constant object, or the direction of motion of a fixed object = the object is moving straight. The magnitude of velocity or speed is constant = the speed is always the same all the time.

## Nonuniform linear motion

### Definition of nonuniform linear motion

Nonuniform linear motion is motion at constant acceleration. In other words, nonuniform linear motion = motion with the magnification of acceleration is constant and the direction of acceleration is constant. Direction of acceleration is constant = direction of velocity is constant = direction of displacement is constant = direction of motion is constant = the object moves in a straight line. The magnitude of constant acceleration means that the magnitude of velocity or speed increases regularly.

## Free fall motion

### Article about the Free fall motion

In everyday life, we often see objects that experience free-fall motion, for example, the motion of fruit falling from a tree, the motion of objects that fall or are dropped from a certain height. Why do objects experience free-fall motion? If observed at a glance, the object experiencing free fall as if it has a fixed speed, or in other words the object does not accelerate. The fact that happens, every object that falls freely experiences a constant acceleration. This reason causes free-fall motion, including the example of nonuniform linear motion. How to prove that objects experiencing free-fall experience constant acceleration or its speed increase?

## Uniform circular motion

### Article about the Uniform circular motion

In everyday life, we often encounter objects that move in a uniform circular motion. One example of an object that undergoes uniform circular motion is the second needle, the minute needle, and the clock needle on the analog clock. The second needle always rotates at an angle of 360o for 60 seconds (one minute) or rotates at a 6o angle for one second. The minute needle always rotates at a 360o angle for 60 minutes (one hour) or rotates at a 6o angle for one minute. Hour needle also always rotates 360o for 24 hours (one day). If an object moves in a regular circle such as a second needle, a minute needle, or a clock needle then the objects are said to be doing the circular motion. Can you think of examples of objects that move in a circular motion?

## The quantities of physics in the circular motion

The quantities of physics in the circular motion include angular displacement, angular velocity, and angular acceleration.

### 1. Angular displacement (θ)

Displacement in circular motion is called angular displacement. Angular displacement including vector quantities, therefore, has magnitude and directions. The direction of angular displacement is usually expressed in a clockwise direction (clockwise or counterclockwise).

There are three units of angular displacement. First, degree (o). One circumference of the circle is equal to 360o. Second, revolution. One circumference of the circle is equal to one revolution. Third, radian. Observe the figure below. If an object moves in a circle then r = the radius of the circle, x = the length of the circular path that the object passes = the circumference of the circle.

## Projectile motion

### Initial velocity (vo) and the component of initial velocity (vox and voy)

An object which moves parabolic always has an initial speed. Because parabolic motion is a combination of movements in the horizontal and vertical directions, the initial velocity also has horizontal and vertical components.

If the object moves parabolically as in Figure 1 and 3 then the initial velocity in the horizontal direction (vox) and the initial velocity in the vertical direction (voy) are calculated using the equation:

## Newton’s law of motion

### 1. Definition of force

Force is something that causes things to accelerate. In other words, force is something that moves, stops, or changes the direction of movement of an object. Force is a vector quantity, and therefore, has a magnitude and direction. The force symbol is F (Force). F is a general symbol of force. There are several types of forces and not all forces have the symbol F. The international system unit is kg m/s2 aka Newton.

### 2. Definition of the net force

The resultant force (ΣF) is the sum of all the forces acting on an object. Force is a vector quantity, so the total force is calculated based on the vector addition rule.

## Friction force

### 1. Definition of the friction force

Friction is a drag that works between the surfaces of objects that touch each other. In this topic, the frictional force studied is related to the frictional force acting between two solid body surfaces that touch. Such as friction between the base of the beam and the floor surface, friction between the shoe base and the floor surface, friction between the wheels of the car and the road surface.

The friction force always works on the surface of solid objects that touch each other, even though the object is very smooth. Even smooth surfaces are actually very rough on a microscopic scale. When an object moves, these microscopic ridges interfere with the motion. At the atomic level, a protrusion on the surface causes atoms to be very close to other surfaces, so that the electric forces between atoms can form chemical bonds, as a union between two surfaces of a moving object. When an object moves, for example when you push a book on the surface of the table, the movement of the book experiences obstacles and finally stops. This is due to the formation and release of the bond.

## Newton’s law of universal gravitation

### Article about the Newton’s law of universal gravitation

In the subject of Newton’s law, it was learned that every object which is initially rest becomes moves, or any object that initially moves becomes rest if there is “something” that moves or stops the object. Something is called “force”. Why does the fruit fall or move towards the surface of the earth after it is released from the stem? Newton’s law states that if the fruit moves, there must be a force acting on the fruit. The force that causes fruit or any object to fall towards the surface of the earth is called the force of gravity.