Uniform movement. Uniform movement What movement is called uneven examples

95. Give examples of uniform movement.
It is very rare, for example, the movement of the Earth around the Sun.

96. Give examples of uneven movement.
The movement of a car, an airplane.

97. The boy is rolling down the mountain on a sled. Can this movement be considered uniform?
No.

98. Sitting in the carriage of a moving passenger train and observing the movement of the oncoming freight train, it seems to us that the freight train goes much faster than our passenger train went before the meeting. Why is this happening?
In a relative passenger train, a freight train moves with the total speed of a passenger and freight train.

99. The driver of a moving vehicle is in motion or at rest in relation to:
a) roads;
b) car seats;
c) gas stations;
d) the sun;
e) trees along the road?
In motion: a, c, d, e
At rest: b

100. Sitting in the carriage of a moving train, we observe in the window a car that goes forward, then seems motionless, and finally moves backward. How can we explain what we see?
Initially, the speed of the car is higher than the speed of the train. Then the speed of the car becomes equal to the speed of the train. Thereafter, the speed of the car decreases compared to the speed of the train.

101. The plane is performing a loop. What trajectory do observers see from the ground?
An annular path.

102. Give examples of the movement of bodies along curved paths relative to the ground.
The movement of planets around the Sun; boat movement along the river; Flight of bird.

103. Give examples of the motion of bodies with a rectilinear trajectory relative to the ground.
Moving train; walking straight person.

104. What kinds of movement do we observe when writing with a ballpoint pen? With chalk?
Uniform and uneven.

105. What parts of the bike does it have straight motion describe rectilinear trajectories relative to the ground, and which ones are curved?
Straightforward: handlebar, saddle, frame.
Curvilinear: pedals, wheels.

106. Why do they say that the sun rises and sets? What is the reference body in this case?
The reference body is considered the Earth.

107. Two cars move along the highway so that some distance between them does not change. Indicate relative to which bodies each of them is at rest and relative to which bodies they move during this period of time.
The cars are at rest in relation to each other. Cars move relative to surrounding objects.

108. Sleds roll down the mountain; the ball rolls down an inclined chute; a stone released from the hands falls. Which of these bodies are moving forward?
A sled from the mountain and a stone released from the hands are moving forward.

109. The book, set on the table in an upright position (Fig. 11, position I), falls from the push and takes position II. At the same time, two points A and B on the cover of the book described the trajectories of AA1 and BB1. Can we say that the book was moving forward? Why?

Do you think you are moving or not when you read this text? Almost every one of you will immediately answer: no, I am not moving. And it will be wrong. Some might say: I'm moving. And they will be wrong too. Because some things in physics are not quite what they seem at first glance.

For example, the concept of mechanical motion in physics always depends on a point (or body) of reference. This is how a person flying in an airplane moves relative to the relatives who remained at home, but is at rest relative to a friend sitting next to him. So bored relatives or a friend sleeping on his shoulder are, in this case, reference bodies for determining whether our aforementioned person is moving or not.

Definition of mechanical movement

In physics, the definition of mechanical motion taught in seventh grade is as follows: the change in the position of the body relative to other bodies over time is called mechanical movement. Examples of mechanical movement in everyday life are the movement of cars, people, and ships. Comets and cats. Air bubbles in a boiling kettle and textbooks in a heavy schoolboy backpack. And every time the statement about the movement or rest of one of these objects (bodies) will be meaningless without indicating the reference body. Therefore, in life we most often, when we talk about motion, mean motion relative to the Earth or static objects - houses, roads, and so on.

Mechanical movement trajectory

It is also impossible not to mention such a characteristic of mechanical movement as a trajectory. The trajectory is the line along which the body moves. For example, shoe prints in the snow, an airplane trail in the sky, and a tear trail on a cheek are all trajectories. They can be straight, curved or broken. But the length of the trajectory, or the sum of the lengths, is the path traversed by the body. The path is denoted by the letter s. And it is measured in meters, centimeters and kilometers, or in inches, yards and feet, depending on which units of measurement are adopted in this country.

Types of mechanical movement: uniform and uneven movement

What are the types of mechanical movement? For example, while driving a car, the driver moves at different speeds when driving in the city and at almost the same speed when driving out onto the highway outside the city. That is, it moves either unevenly or evenly. So the movement, depending on the distance traveled for equal periods of time, is called uniform or uneven.

Examples of uniform and uneven movement

There are very few examples of uniform motion in nature. The Earth moves almost evenly around the Sun, raindrops are dripping, bubbles in soda pop up. Even a bullet fired from a pistol moves in a straight line and evenly only at first glance. From the friction against the air and the Earth's gravity, its flight gradually becomes slower, and the trajectory decreases. In space, a bullet can move really straight and evenly until it collides with some other body. And with uneven movement, the situation is much better - there are many examples. The flight of a ball during a football game, the movement of a lion hunting prey, the travel of a seventh grader's gum and a butterfly flitting over a flower are all examples of uneven mechanical movement of bodies.

Definition of mechanical movement

Mechanical movement trajectory

Types of mechanical movement: uniform and uneven movement

What are the types of mechanical movement? For example, while driving a car, the driver moves at different speeds when driving through the city and at almost the same speed when driving out onto the highway outside the city. That is, it moves either unevenly or evenly. So the movement, depending on the distance traveled for equal periods of time, is called uniform or uneven.

Examples of uniform and uneven movement

Topic: Body Interaction

Lesson:Uniform and uneven movement. Speed

Consider two examples of the movement of two bodies. The first body is a car moving along a straight, deserted street. The second is a sleigh, which, accelerating, rolls down from a snow slide. The trajectory of both bodies is a straight line. From the last lesson, you know that such a movement is called rectilinear. But there is a difference in the movements of the car and the sled. The car travels the same lengths of the path for equal periods of time. And the sledges pass more and more at equal intervals of time, that is, different sections of the path. The first type of movement (the movement of the car in our example) is called uniform movement. The second type of movement (the movement of the sled in our example) is called uneven movement.

uniform is a movement in which for any equal time intervals the body travels the same path segments.

An uneven movement is such a movement in which, at equal intervals of time, the body travels different segments of the path.

Note the words “any equal time intervals” in the first definition. The fact is that sometimes it is possible to specially select such intervals of time for which the body passes equal paths, but the movement will not be uniform. For example, the end of the second hand of an electronic clock travels the same paths every second. But this will not be a uniform movement, since the arrow moves in leaps and bounds.

Rice. 1. An example of uniform motion. Every second this car travels 50 meters.

Rice. 2. An example of uneven movement. Accelerating, every second the sledges pass more and more sections of the path.

In our examples, the bodies were moving in a straight line. But the concepts of uniform and non-uniform motion are equally applicable to the movement of bodies along curvilinear trajectories.

We come across the concept of speed quite often. From the mathematics course, you are perfectly familiar with this concept, and it is easy for you to calculate the speed of a pedestrian who walked 5 kilometers in 1.5 hours. To do this, it is enough to divide the path traveled by the pedestrian by the time spent on the passage of this path. Of course, this assumes that the pedestrian was moving evenly.

The speed of uniform movement is called physical size, numerically equal to the ratio of the path traversed by the body to the time spent on the passage of this path.

The speed is indicated by a letter. Thus, the formula for calculating the speed is:

V The international system units path, like any length, is measured in meters, and time - in seconds. Hence, speed is measured in meters per second.

In physics, off-system units of measurement of speed are also very often used. For example, a car moves at a speed of 72 kilometers per hour (km / h), the speed of light in a vacuum is 300,000 kilometers per second (km / s), the speed of a pedestrian is 80 meters per minute (m / min), but the speed of a snail is only 0.006 centimeters per second (cm / s).

Rice. 3. Speed can be measured in various non-system units.

It is customary to translate non-system units of measurement into the SI system. Let's see how this is done. For example, to convert kilometers per hour to meters per second, you need to remember that 1 km = 1000 m, 1 h = 3600 s. Then

A similar translation can be carried out with any other non-systemic unit of measurement.

Is it possible to say where the car will be if it was moving at a speed of 72 km / h for, for example, two hours? It turns out not. Indeed, in order to determine the position of a body in space, it is necessary to know not only the path traversed by the body, but also the direction of its movement. The car in our example could move at a speed of 72 km / h in any direction.

A way out can be found by assigning not only a numerical value (72 km / h) to the speed, but also the direction (northward, southwestward, along a given X-axis, etc.).

The quantities for which not only the numerical value, but also the direction are important, are called vector quantities.

Hence, speed - vector quantity (vector).

Let's look at an example. Two bodies move towards each other, one at a speed of 10 m / s, the other at a speed of 30 m / s. To depict this movement in the figure, we need to choose the direction of the coordinate axis along which these bodies move (X-axis). Bodies can be depicted conventionally, for example, in the form of squares. The directions of the speed of the bodies are indicated with the help of arrows. Arrows let you indicate that bodies are moving in opposite directions. In addition, the figure is scaled: the arrow representing the speed of the second body is three times longer than the arrow representing the speed of the first body, since the numerical value of the speed of the second body is three times greater by the condition.

Rice. 4. Image of vectors of velocity of two bodies

Please note that when we draw the speed symbol next to the arrow, which indicates its direction, then a small arrow is placed above the letter:. This arrow indicates that we are talking about a velocity vector (i.e., both the numerical value and the direction of the velocity are indicated). Arrows are not shown next to the numbers 10 m / s and 30 m / s above the speed symbols. A symbol without an arrow indicates the numerical value of a vector.

So, mechanical movement can be uniform and uneven. The characteristic of movement is speed. In the case of uniform motion, to find the numerical value of the speed, it is sufficient to divide the path traversed by the body by the time it takes this path. In the SI system, speed is measured in meters per second, but there are many non-SI units of speed. In addition to the numerical value, the speed is also characterized by the direction. That is, speed is a vector quantity. To indicate the velocity vector, a small arrow is placed above the velocity symbol. To indicate the numerical value of the speed, such an arrow is not placed.

Bibliography

1. Peryshkin A.V. Physics. 7 cl. - 14th ed., Stereotype. - M .: Bustard, 2010.

2. Peryshkin A.V. Collection of problems in physics, grades 7 - 9: 5th ed., Stereotype. - M: Publishing house "Exam", 2010.

3. Lukashik V.I., Ivanova E.V. Collection of problems in physics for grades 7 - 9 educational institutions... - 17th ed. - M .: Education, 2004.

1. Unified collection of Digital Educational Resources ().

2. Unified collection of Digital Educational Resources ().

Homework

Lukashik V.I., Ivanova E.V. Collection of problems in physics for grades 7 - 9

Uniform movement- movement along a straight line with a constant (both in absolute value and in direction) speed. With uniform motion, the paths that the body travels at equal intervals of time are also equal.

For a kinematic description of the motion, we will position the OX axis along the direction of motion. To determine the displacement of a body with uniform rectilinear motion, one X coordinate is sufficient. The projections of displacement and velocity onto the coordinate axis can be considered as algebraic quantities.

Let at time t 1 the body was at a point with coordinate x 1, and at time t 2 - at a point with coordinate x 2. Then the projection of the point displacement on the OX axis will be written as:

∆ s = x 2 - x 1.

Depending on the direction of the axis and the direction of movement of the body, this value can be either positive or negative. With rectilinear and uniform movement, the modulus of movement of the body coincides with the traversed path. The speed of uniform rectilinear movement is determined by the formula:

v = ∆ s ∆ t = x 2 - x 1 t 2 - t 1

If v> 0, the body moves along the OX axis in the positive direction. Otherwise, it is negative.

The law of motion of a body with uniform rectilinear motion is described by a linear algebraic equation.

Equation of body motion with uniform rectilinear motion

x (t) = x 0 + v t

v = c o n s t; x 0 - coordinate of the body (point) at time t = 0.

An example of a graph of uniform movement is shown in the figure below.

There are two graphs describing the motion of bodies 1 and 2. As you can see, body 1 at time t = 0 was at the point x = - 3.

From point x 1 to point x 2, the body moved in two seconds. The movement of the body was three meters.

∆ t = t 2 - t 1 = 6 - 4 = 2 s

∆ s = 6 - 3 = 3 m.

Knowing this, you can find the speed of the body.

v = ∆ s ∆ t = 1.5 m s 2

There is another way to determine the speed: from the graph it can be found as the ratio of the sides BC and AC of the triangle ABC.

v = ∆ s ∆ t = B C A C.

Moreover, the greater the angle that forms the graph with the time axis, the more speed... They also say that the speed is equal to the tangent of the angle α.

Similar calculations are carried out for the second case of motion. Consider now new schedule, depicting movement using line segments. This is the so-called piecewise line graph.

The movement depicted on it is uneven. The speed of the body changes instantly at the break points of the graph, and each segment of the path to the new break point, the body moves uniformly with a new speed.

From the graph, we see that the speed changed at times t = 4 s, t = 7 s, t = 9 s. The speed values are also easily found from the graph.

Note that the path and displacement do not coincide for the movement described by the piecewise linear graph. For example, in the time interval from zero to seven seconds, the body covered a distance of 8 meters. In this case, the movement of the body is equal to zero.

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