Physics

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.

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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.

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Article about the Gravitational field and gravitational field strength

When you push a book on the table surface until the book moves, your hand touches the book. Likewise, when you tie an object with a piece of rope, then pull it until it moves, your hand touches the rope, the rope touches the object. In this case, the push force, pull force, tension force of the rope, and forces like this are called touch forces or contact forces. Earth’s gravitational force that pulls the fruit falling toward the surface of the earth. Or, the gravitational force of the earth that pulls the moon to the orbit of the earth occurs without touch between the earth and the fruit and moon.

Therefore, gravitational forces or forces like this are called non-touch forces. How could fruit fall and the moon “fall” towards the earth without touching between the earth with fruit and moon? Scientists, including Newton, find it difficult to imagine the concept of non-touch force. In order to more easily imagine and understand the concept of non-touch force, the concept of field is raised.

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Definition of the parallel plate capacitor

The parallel plate capacitor is a capacitor that consists of two parallel conductor plates, each plate having an equal cross-sectional area (A) and two plates separated by a certain distance (d), as shown in the figure left. One of the conductor plates is positively charged (+Q) while the other conductor plate is negatively charged (-Q), where the amount of electric charge on each plate is equal. So that the charge does not move to the air molecule, the capacitor is isolated from the environment, and between the two plates, there is a vacuum.

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Article about Kepler’s law

Do you still remember the memories of first riding a car? When in a moving car, you see as if a tree or building is moving. At that time, you might think the trees or buildings are moving, while you and the car are in rest. In fact, you and the car move, while the trees or buildings are rest. This experience of fake motion is actually experienced every day. Every morning, “sunrises” on the eastern horizon then move west and “sets” on the western horizon in the afternoon.

Likewise, at night, you often see the moon moving from east to west. Have you ever thought or guessed that the sun and moon moved around the earth, while the earth was in rest?

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Article about Moment of force

1. Lever arm

Review an object that rotates, such as the door of a room. When the door is opened or closed, the door rotates. The hinges that connect the door to the wall act as the axis of rotation.

The door image is seen from above. Review an example where the door is pushed in the same two forces that have the same magnitude and direction, where the direction of the force is perpendicular to the door. At first, the door is pushed with a force of F₁, r₁ from the axis of rotation. Subsequently, the door is pushed with the force of F₂, r₂ away from the axis of rotation. Although the magnitude and direction of the force F₁ = F₂, the force of F₂ causes the door to rotate faster than the force of F₁. In other words, the force of F₂ causes a greater angular acceleration compared to the force of F₁. You can prove this.

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Article about the Newton’s second law on rotational motion

4.1 The relationship between the moment of force, the moment of inertia, and the angular acceleration

If there is a resultant force (ΣF) acting on an object with mass (m) then the object moves linearly with a certain acceleration (a). The relationship between the resultant force, mass, and acceleration is expressed by the equation:

ΣF = m a

This is the equation of Newton‘s second law.

The quantities of the rotational motion which are identical to the resultant force (ΣF) in linear motion is the resultant moment of force (Στ). The quantities of the rotational motion that are identical to mass (m) in linear motion is the moment of inertia (I). The quantities of the rotational motion that are identical to acceleration (a) in linear motion is the angular acceleration (α).

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1. Definition of the center of gravity

A rigid body is composed of many particles; therefore, the gravitational force acting on each of these particles. In other words, each particle has its weight. The center of gravity of an object is a point on the object where the weight of all parts of the object is considered to be centered at that point.

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Article about the Types of equilibrium of the rigid body

Not all things we find in everyday life always rest. Maybe at first the object rest, but if it is moved (for example by the wind) objects can move. The problem is, whether after moving, objects return to their original position or not. This depends on the type of balance of the object. After moving, there will be three possibilities, namely:

(1) the object returns to its original position,

(2) the object moves away from its original position,

(3) the object remains in its new position.

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Article about the Equilibrium of a rigid body

1. First condition

Newton’s Second Law states that if the resultant force on an object (an object considered as a single particle) is not zero,

then the object will move with constant acceleration, where the direction of the object’s motion = the direction of the total force. If the resultant force is zero, then the object is at rest or moving at a constant speed.

ΣF = m a

When an object is at rest or moves at a constant speed, the object does not have acceleration (a). Because acceleration (a) = 0, the equation above changes to:

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