This article is about the movement of bodies. In this article you will find out what this is all about, which terms and classifications are important to you and how you use them in examples. We can assign the chapter to mechanics and thus to the subject of physics.
- Classification of mechanics
- what is a body
- Model point mass and rigid body
- What is a movement?
- Classification of movements according to dimension, shape and type
- Parameters and relationships (equations of motion)
- Throws as a superimposition of movements
- Summary of the most important information
Basic mechanics
Before we deal more closely with the question of what movements of bodies are and what types of movements exist, let us briefly repeat some basic principles of mechanics.
The field of mechanics deals with stationary and moving bodies and the forces that occur. In the separate chapter we have already got to know different possibilities for dividing the areas in mechanics. It is important to distinguish between the classic mechanics. Several sub-areas can be defined, as shown in the following figure.
Figure 1: Classification of classical mechanics
The division into the various subject areas is based on movements and the forces at work. This is how the so-called deals kinematics with mechanical movements without the consideration of acting forces. She thus deals with the pure movements of a body. In contrast to this is the sub-area of Dynamics. The acting forces are taken into account, which is why it is also called the theory of forces. In addition, a distinction can be made between forces on bodies at rest (statics) and forces as the cause of movements (kinetics). In the following we will focus on the sub-area of kinematicsso the teaching of movements, restrict.
Movement of bodies – what is it all about?
The topic of kinematics therefore deals with the movements of bodies. But what exactly is a body and how is a movement defined?
Body
In order for us to be able to use and understand the body as a physical object for movements, we must first clarify what exactly a body is. We have already got to know this term in the chapter on fundamental quantities and properties of bodies and materials.
A Body is therefore an object that a Space occupies, from one or more fabrics consists and one Dimensions owns.
The figure below shows an example of a solid body.
Figure 2: Aluminum cube as body
The body «aluminium cube» spans a three-dimensional space, the so-called volume. It consists of material Aluminum, what with the characteristic material constant, the density, has a value of 2.70 g/cm³. Density describes the mass per unit volume. The dimensions and the fabric then result in a specific one Dimensions for the cube shown. In kinematics, i.e. the study of movements, the components volume, substance and mass do not always play a role. In some cases it can therefore be useful to use the point mass and rigid body models. We have already addressed these in the chapter on fundamental quantities and properties of bodies and materials.
Mass point and rigid body
The models mass point and rigid body are used to describe movements as a simplification of the complex processes, depending on whether the dimensions of the body play a role or not.
mass point:
In physics, a mass point or even one point mass assumed as an idealized model of a body. The entire mass of the body is summarized in a single point (usually the center of gravity). So the dimensions are disregarded and the pure movement is considered. Figure 3 shows the simplification of the example of our aluminum cube.
Figure 3: Aluminum cube as a mass point
Rigid body:
Another idealization is the model of the rigid body. It is assumed that the body cannot be deformed by external forces. It keeps its shape and neither expands nor compresses. So any two points A and B of the body always have the same distance to each other.
Figure 4: Cube as a rigid body
We will show later when we use the models of the mass point and the rigid body in motion.
We know what a body is and what simplifications can be applied to real bodies. But what exactly is a movement?
movement
The kinematic processes deal with mechanical movements. We encounter them every day, we carry them out ourselves and even see them. For the physical description, however, a reference system is first necessary. Changes the body his location or its position in relation to the frame of reference, it introduces a movement out. To illustrate this, we use our cube again.
Figure 5: Cube in motion
This moves on a subsoil from one place to another, thus changing its position on the subsoil. Without the ground as a reference system, the movement of the cube could not be specified. So we need one Body together with one frame of reference, in order to be able to adequately describe movements. What triggered the movement of the cube in our example is not relevant in kinematics, but is considered in the separate sub-area of dynamics.
We already know what the terms body and movement are all about. But how can a body move?
classification of movements
In physics, the movements of bodies can be classified based on various factors: dimension, shape and type. As we will see below, the classifications are closely linked.
movement dimensions
Our aluminum cube example shows a movement of the body from one position to another position on the ground. It has therefore only changed its position in the horizontal direction. However, a movement can also run in other directions. We can use the three dimensions of a coordinate system as a reference.
Figure 6: Dimensions of the movement
For the one-dimensional movement, the coordinates in the horizontal direction are sufficient to fully describe the change in position. Movements in several dimensions of the surface and space require two or three coordinates for the correct definition of the position of the body. Here, the mathematical knowledge of vectors and vector decomposition is used.
forms of movement
In addition to the dimensions, the movements can be divided into different forms of movement. This division is based on their spatial History: hers lane shape. The path describes the form in which the body covers the movement.
Figure 7: Forms of movement
When moving in a straight line, the body moves in a straight line. It is therefore a translational or linear Movement. In this case, the model of the mass point used because the dimensions are not relevant for the translatory movement. In contrast to this is the rotation. The body performs a movement on a circular train off. Here, the sub-area of kinematics often uses the model of the rigid body, since the body is assumed not to deform during motion. As a third form of movement, oscillation is listed. During an oscillation, the body always moves back and forth between two reversal points on the same path. Known examples of a periodic (recurring) movements are rocking with a swing or a pendulum.
movement types
In addition to the forms of movement, movements can also be divided into different types of movements. Here, the kinematic processes according to their temporal different course. The conditions for the speed and acceleration of the body must be observed. If you are no longer familiar with the terms time, location, speed and acceleration, simply read the relevant chapter again.
Figure 8: Movement types
Characteristic of a uniform movement is the constant speed of the body. He will neither speed up nor slow down during the whole process. As a result, its speed does not change during the movement, which means that with uniform movements, the acceleration same zero is.
In contrast to this is the non-uniform movement of a body. Through the speedmodification of the body, this is no longer constant, which means that an acceleration must prevail. In the case of uniformly accelerated motion, this acceleration is constant again. Bodies that move with uneven acceleration have neither constant speed nor constant acceleration and can generally only be solved with differential equations. Therefore, the tasks in physics in the school career are usually limited to the following types of movement:
- uniform movement
- uniformly accelerated movement
We have already learned about the classification of movements. In mechanics, it is important to describe the kinematic processes using different quantities and equations.
equations of motion
In the chapter basic sizes and properties of bodies and materials you have already got to know the most important sizes for describing a movement:
- time
- location
- speed
- acceleration
These are closely related to each other. The relationships between the parameters are illustrated in various diagrams. The following figure shows the typical diagrams with independent examples.
Figure 9: Time-dependent diagrams
For example, the distance-time diagram in example 1 shows which distance was covered after which time. The x-axis is the time axis with the associated unit.
As you should already know from mathematics, the graphs in charts can be described using various equations. For this we look at the speed-time diagram in example 2 and set up the equation for the graph according to the known rules.
The example shows that the associated speed can be calculated for any point in time t using the equation of motion in the graph. This is not only possible for the relationship between speed and time, but also for all other examples shown and other relationships. They can each be characterized graphically and with the help of equations.
The description of a movement using parameters and their relationships play an important role in mechanics. Each movement can thus be clearly defined. You can find more about the equations of motion of the individual movements in the respective separate chapters.
In this context, the teaching of movements is still…