School Encyclopedia. Types of movement. The task of kinematics What types of movement do you know

Details Category: Mechanics Posted on 17.03.2014 18:55 Views: 16143

Mechanical movement is considered for material point and for solid body.

Movement of a material point

translational movement of an absolutely rigid body is a mechanical movement, during which any line segment associated with this body is always parallel to itself at any moment in time.

If you mentally connect any two points of a rigid body with a straight line, then the resulting segment will always be parallel to itself in the process of translational motion.

In translational motion, all points of the body move in the same way. That is, they cover the same distance in the same time intervals and move in the same direction.

Examples of translational motion: the movement of an elevator car, cups of mechanical scales, a sledge racing downhill, bicycle pedals, a train platform, engine pistons relative to cylinders.

rotational movement

With rotational motion, all points of the physical body move in circles. All these circles lie in planes parallel to each other. And the centers of rotation of all points are located on one fixed straight line, which is called axis of rotation. Circles described by points lie in parallel planes. And these planes are perpendicular to the axis of rotation.

Rotational motion is very common. Thus, the movement of points on the rim of a wheel is an example of rotational movement. The rotational motion describes the fan propeller, etc.

Rotational motion is characterized by the following physical quantities: angular velocity of rotation, period of rotation, frequency of rotation, linear velocity of a point.

angular velocity a body with uniform rotation is called a value equal to the ratio of the angle of rotation to the time interval during which this rotation occurred.

The time it takes a body to complete one revolution is called rotation period (T).

The number of revolutions a body makes per unit of time is called speed (f).

The rotation frequency and the period are related by the relation T = 1/f.

If the point is at a distance R from the center of rotation, then its linear velocity is determined by the formula:

The concept of motion is one of the philosophical categories, along with others, such as matter and time, which serve as the basis for the materialistic sciences. But we will not consider this issue in such depth now. Let's just see what they are and what types of movement there are from the point of view of classical mechanics.

In physics there is a special section of mechanics - kinematics. It also studies its types, and considers the very movement of an object without its interaction with other bodies. The change in the position of the body relative to others in a given period of time is called mechanical movement, which in Greek sounds like “kinematics”.

Movement permeates our whole life. People and animals move, rivers and air, Earth and Sun move. It is quite possible that it was the initial observation of the processes of displacement by the ancient Greeks that subsequently led to the creation of such a science as physics - at least to the creation of such sections of it as mechanics and kinematics.

There are the following types of mechanical translational and oscillatory. is characterized by the fact that all points of the body move in the same direction at the same distance in the same time interval. During rotational movement or rotation, any points of an object move along circles whose centers are located on a line called the axis of rotation. An oscillatory movement is a movement that periodically completely or partially repeats.

Considering the types of movement, we introduced two concepts - the movement of a point and a body. Strictly speaking, the description of the movement of the body as a whole is nothing more than a description of the movement of its various points. Therefore, it is often enough to characterize the movement of a point in order to understand the movement of the body itself. Translational motion is characterized by the same movement of all points of the body, so we can assume that, having considered the movement of one point, we have determined how the body moves.

However, all of the above types of movement are not limited. The movement can be rectilinear or curvilinear, uniform or uniformly accelerated. To describe the nature of the movement, you must again introduce a new concept - the trajectory. It can be defined as the line along which the body moves. When we pass a pen over paper, we see the trace that remains behind it. This is the pen path.

Now, with the introduction of the concept of a trajectory, we can take a closer look at the previously noted types of movement. So, with translational different points may be different, but they remain parallel to themselves. An example is the body (but not the wheels) of a car moving straight ahead. The movement of a needle in a sewing machine or a piston in a motor cylinder are other examples of translational motion.

The concept of a trajectory gives an explanation of rectilinear and curvilinear motion. If the trajectory is a straight line, then it is if not, then it is curvilinear. As an example of rotational curvilinear motion, one can cite Rotation will not be translational motion.

Of course, all of the above is only part of what needs to be considered when touching on the topic “Types of movement”. For a complete description of the nature of the movement, it is necessary to introduce new concepts - such as speed, distance traveled, frame of reference. Then it will be possible to understand in more detail the nature of the movement of both a single point and the body as a whole. But even the above material allows a little glimpse into the many-sided world of the movement.

The article considers the types of motion accepted in classical physics, gives examples of their different types and describes their distinctive features.

There are six main types of osteokinetic (voluntary or active) movement that a body segment can perform (Figure 2.2).

bending is a movement in which the angle between the bones that form the joint decreases. Examples of this type of movement are bending the elbow joint, tilting (bending) the head forward during prayer, bending the leg at the knee joint (Fig. 2.2, a).

Extension represents an increase in the angle between the bones that form the joint, while straightening its kinematic chain. When the extension exceeds the anatomical position, they speak of hyperextension (Fig. 2.2, b).

Abduction is the movement of a body segment away from middle line body or from the part of the body to which it is attached. Examples of abduction are movements of the arms or legs to the sides (Fig. 2.2, in).

The Science of Flexibility

Rice. 2.2. Examples of the six main types of movements:

a- flexion of the knee joint; b- hyperextension of the hip joint; in- abduction of arms and legs; G- adduction of arms and legs; d- rotation of the head and upper body;

e- hand circumduction (Alter, 1988)

Casting is the movement opposite to abduction. This is the movement of a body segment towards the midline of the body or towards the part of the body to which it is attached. An example is bringing the arms to the body (Fig. 2.2, d).

Rotation- movement of a body segment around its axis. An example of such a movement is turning the head from side to side (Fig. 2.2, e).

Circumduction represents a movement in which the end of a segment describes a circle. Circumduction is often a combination of flexion, adduction, extension, and abduction. An example is circular movements with the hands (Fig. 2.2, e).

Special moves. There are a number of terms that are used to describe certain special types movements.

Chapter 2 . Osteacogia and arthrology

Supination is the outward rotation of the forearm. Thus, this movement is associated with turning the palm forward (from a standing position with the arms at the sides).

Pronation is an inward rotation of the forearm. This movement is used when turning a doorknob or a screwdriver.

Inversion- turning the sole of the foot inward. This movement often occurs when the ankle is sprained.

eversion- rotation of the sole of the foot outward.

There are other types of movements that occur in the ankle and plantar joints: back bend, or back foot extension("take the socks over"); sole flexion(pull up socks), or plantar flexion.

The last two types of special moves are protraction and retraction shoulder girdle. In the first case, forward movement of the shoulder, shoulder blade and collarbone is performed. This movement is observed during the lifting phase of a push-up. Retraction is a backward movement of the shoulder, scapula and collarbone. Examples of retraction can be found in rowing and archery (pulling back the string).

Mechanical movement body is called the change in its position in space relative to other bodies over time. For example, a person riding an escalator in the subway is at rest relative to the escalator itself and moves relative to the walls of the tunnel

Kinds mechanical movement:

rectilinear and curvilinear - according to the shape of the trajectory;
uniform and uneven - according to the law of motion.

mechanical movement relatively. This is manifested in the fact that the shape of the trajectory, displacement, speed and other characteristics of the movement of the body depend on the choice of the frame of reference.

The body relative to which the motion is considered is called reference body. The coordinate system, the body of reference with which it is associated, and the instrument for measuring time form reference system , relative to which the motion of the body is considered.

Sometimes the size of the body compared to the distance to it can be neglected. In these cases, the body is considered material point.

Determining the position of the body at any given time is main task of mechanics.

The important characteristics of movement are trajectory of a material point, displacement, velocity and acceleration. The line along which it moves material point, called trajectory . The length of the trajectory is called the path (L). The unit of measurement of the path is 1m. The vector connecting the start and end points of the trajectory is called displacement (). Displacement unit-1 m.

The simplest form of motion is uniform rectilinear motion. A motion in which the body makes the same displacements for any equal intervals of time is called rectilinear. uniform movement. Speed() - vector physical quantity, which characterizes the speed of movement of the body, numerically equal to the ratio of movement in a small period of time to the value of this interval. The defining formula for the speed has the form v = s/t. Speed unit - m/s. Measure speed with a speedometer.

The movement of a body, in which its speed changes in the same way for any interval of time, is called uniformly accelerated or equally variable.

— a physical quantity that characterizes the rate of change in speed and is numerically equal to the ratio of the vector of change in speed per unit time. Unit of acceleration in SI — m/s 2 .

uniformly accelerated, if the modulus of speed increases. - the condition of uniformly accelerated motion. For example, accelerating vehicles - cars, trains and free fall of bodies near the Earth's surface ( = ).

The uniform motion is called equally slow if the modulus of speed decreases. is the condition of uniformly slow motion.

Instant Speed uniformly accelerated rectilinear motion

Parameter name	Meaning
Article subject:	Types of movement
Rubric (thematic category)	Maths

HYDRODYNAMICS

HYDRODYNAMICS

Types of movement

Pressurized, non-pressurized movement and free jets

Trajectory, streamline, elementary trickle

Flow elements

Fluid consumption and average speed

Continuity equation

Differential equations of motion of an ideal fluid

Integration differential equations motion of an ideal fluid. Bernoulli's equation for an elementary stream of an ideal liquid

Bernoulli's equation for an elementary stream of a real liquid

Bernoulli's equation for real fluid flow

Geometric interpretation of the Bernoulli equation

Two fluid motion modes

The main equation of the steady state uniform motion

laminar flow

Turbulent mode

THE CONCEPT OF HYDRAULICALLY SMOOTH AND ROUGH SURFACES

Determination of head loss along the length

Local head loss

LIQUID OUTFLOW THROUGH NOZZLES

Vacuum value in the compressed section of the nozzle

Nozzle length limit

Fluid outflow at variable pressure

He studies the laws of fluid motion and interaction with washed bodies.

The reason for the movement is the action of forces on the fluid.

The main parameters characterizing the movement are internal pressure and velocity at individual points. The pressure is called hydrodynamic.

In general, velocity and pressure are functions of coordinate and time.

The task of hydrodynamics is to study the interaction between velocity and pressure at individual points.

p=f(x,y,z,t), u=g(x,y,z,t).

Steady - p and u do not depend on time, ᴛ.ᴇ.

p=f(x,y,z), u=g(x,y,z) or dp/dt=0, du/dt=0.

The steady motion must be uniform and uneven.

Uniform - speed, and in some cases pressure does not change along the flow.

Types of movement - concept and types. Classification and features of the category "Types of movement" 2017, 2018.

- Kinematics of a rigid body. General concepts. Problems of kinematics of a rigid body. Types of motion of a rigid body.

Literature: . Questions for self-test: 1. Formulate the main tasks of kinematics solid body. 2. List the types of motion of a rigid body. Translational motion. Translational motion of a rigid body. Theorem on trajectories, velocities and accelerations of points... .