Physics

# Introduction of Kinematics

Under the kinematics is the study of movements and their laws, without having it be noted the causes that cause these movements or influence.

There are different types of movements which are usually like this distinction or divided:

#### Rectilinear movement (translation)

A body moves straight forward in one direction and it further away from the starting point.

The speed can be constant (uniform motion) or change (non-uniform movement).

Examples:

• Railway train
• Falling stone
• Rolling ball

#### Circular motion or rotation (rotation)

A body moves in a closed orbit (circular orbit) and keeps returning to a specific location. He goes through each point of its orbit once each in the same sense.

Examples:

• Wheel of a car
• Carousel
• Circular saw
• Fan

#### Vibration (oscillation)

A body moves back and forth between two reversal points on the same line. He runs through every point of the course twice in the opposite direction.

Examples:

• Swing
• Pendulum of clock
• String a guitar
• Weight of a coil spring

A process in which a certain State returns after same time periods, called periodic process.

A movement in which a body again and again crosses the same way and always returns to its starting point, is called periodic movement.

Circular movements and vibrations it is so periodic movements.

#### What is a movement at all?

Although the answer to this question appears first banal, it’s still not possible to make an objective statement about whether moves a body or not.

Movement could be defined as local or change of position of a body.

But who is to judge?

Following questions illustrate, that determine whether a body at rest or in motion, lens cannot be answered:

1. you drive a train, your bag is next to you.
Is the case in motion or at rest?
2. you are running on a treadmill and have set a speed of 12 km/h.
Are you moving or at rest?

Obviously, the answer to these questions depends from which point of reference of the operation is considered.

You’re sitting in the train, you’d see the bag alone. Is the same process but from someone on the train platform from observed, so he will claim the bag is in motion.

For a viewer from the outside, you stay on the treadmill alone, even though you’re moving relative to the band with the speed.

A more precise definition of movement could be so:

Movement is a location or change of position of a body relative to other bodies or a frame of reference.

#### Reference systems

A reference system is a coordinate system that is bound to a reference body and thus sets a reference point. In addition, you need a clock to describe the timing as a movement.

The choice of the reference body is arbitrary. Often, the Earth’s surface as the reference body is chosen.

The bag from the example above is from the reference system of “Earth” on the move, while she considered “train” of a reference system alone is.

Rest and motion are relative and depends on the chosen reference scheme. It is therefore the relativity of motion.

The answer to the question whether a body at rest or moves, thus depends on the choice of the reference system.

All reference systems that move uniformly and straight to each other, are on an equal footing. There is no absolute reference system. The same laws of physics, including the inertia law apply in all unaccelerated reference systems.
One such reference systems therefore called Inertial system (derived from the Latin “inertia” = inertia).

#### Description of movements

Certain sizes are necessary to describe a movement, and

• Place
• Time

To examine the movement of the body, the location of the body must be determined at different times.

On the following page, you will find an example of an investigation as well as the evaluation of appropriate measurement points.