Speed:
- Speed is a vector quantity that characterizes the speed of movement and the direction of movement.
- Speed(in engineering) - the degree of change in torque, speed and direction of movement transmitted from the engine to the wheel (working body), by changing the characteristics of the transmission (for example, by changing the gear ratio).
- Speed is a kind of climbing.
- Speed - Russian tracing paper from English. speed- the same as speed, speed - a slang name for a type of psychostimulant amphetamines.
- Speed - the name of the Soviet missile system 15P666 with a medium-range missile.
Movies
- Speed - film (USSR), 1983.
- Speed - Movie (USA), 1994.
- Speed 2: Cruise Control - Movie (USA), 1997.
Addition of speeds
By revising complex movement(when a point or a body moves in one frame of reference, and this frame of reference, in turn, moves relative to another frame), the question arises about the relationship of velocities in two frames of reference.
classical mechanics
Main article: Velocity addition theoremIn classical mechanics absolute speed point is equal to the vector sum of its relative and translational velocities:
V → a = v → r + v → e. (\displaystyle (\vec (v))_(a)=(\vec (v))_(r)+(\vec (v))_(e).)
This equality is the content of the statement of the theorem on the addition of velocities.
In plain language: The speed of the body relative to the fixed frame of reference is equal to the vector sum of the speed of this body relative to the moving frame of reference and the speed (relative to the fixed frame) of that point of the moving frame of reference at which this moment time is the body.
Examples
- The absolute speed of a fly crawling along the radius of a rotating gramophone record is equal to the sum of the speed of its movement relative to the record and the speed that the point of the record under the fly has relative to the ground (that is, from which the record carries it due to its rotation).
- If a person walks along the corridor of the car at a speed of 5 kilometers per hour relative to the car, and the car moves at a speed of 50 kilometers per hour relative to the Earth, then the person moves relative to the Earth at a speed of 50 + 5 = 55 kilometers per hour when walking in the direction of the train, and at a speed of 50 - 5 = 45 kilometers per hour when he goes in the opposite direction. If a person in the carriage corridor moves relative to the Earth at a speed of 55 kilometers per hour, and a train at a speed of 50 kilometers per hour, then the speed of a person relative to the train is 55 - 50 = 5 kilometers per hour.
- If the waves move relative to the coast at a speed of 30 kilometers per hour, and the ship also at a speed of 30 kilometers per hour, then the waves move relative to the ship at a speed of 30 - 30 = 0 kilometers per hour, that is, they become stationary relative to the ship.
Relativistic mechanics
In the 19th century, physics faced the problem of extending this rule for adding velocities to optical (electromagnetic) processes. In essence, there was a conflict between two ideas of classical mechanics (the first is the Space-time of Newton's theory, the second is the principle of relativity), transferred to new area- The theory of electromagnetic processes.
For example, if we consider the example of waves on the surface of water from the previous section and try to generalize to electromagnetic waves, then we get a contradiction with observations (see, for example, Michelson's experiment).
The classical rule for adding velocities corresponds to the transformation of coordinates from one system of axes to another system, moving relative to the first without acceleration. If, with such a transformation, we retain the concept of simultaneity, that is, we can consider two events to be simultaneous not only when they are registered in one coordinate system, but also in any other inertial system, then the transformations are called Galilean. In addition, with Galilean transformations, the spatial distance between two points - the difference between their coordinates in one inertial frame of reference - is always equal to their distance in another inertial frame.
The second idea is the principle of relativity. Being on a ship moving uniformly and rectilinearly, it is impossible to detect its movement by some internal mechanical effects. Does this principle extend to optical effects? Is it possible to detect the absolute motion of the system from the optical or, what is the same, electrodynamic effects caused by this motion? Intuition (rather explicitly related to classical principle relativity) says that absolute motion cannot be detected by any kind of observation. But if light propagates at a certain speed relative to each of the moving inertial frames, then this speed will change when moving from one frame to another. This follows from the classical rule for adding velocities. Speaking mathematically, the magnitude of the speed of light will not be invariant under the Galilean transformations. This violates the principle of relativity, or rather, does not allow the principle of relativity to be extended to optical processes. Thus, electrodynamics destroyed the connection between two seemingly obvious provisions of classical physics - the rule of addition of velocities and the principle of relativity. Moreover, these two positions as applied to electrodynamics turned out to be incompatible.
The special theory of relativity provides an answer to this question. It expands the concept of the principle of relativity, extending it to optical processes as well. At the same time, the special theory of relativity radically changes the concept of space and time. In this case, the rule for adding velocities is not completely canceled, but only refined for high speeds using the Lorentz transformation:
v r e l = v 1 + v 2 1 + v 1 v 2 c 2 . (\displaystyle v_(rel)=(\frac ((v)_(1)+(v)_(2))(1+(\dfrac ((v)_(1)(v)_(2)) (c^(2))))).)
It can be seen that in the case when v / c → 0 (\displaystyle v/c\rightarrow 0) , the Lorentz transformations turn into Galilean transformations. This suggests that mechanics in special relativity reduces to Newtonian mechanics at speeds that are small compared to the speed of light. This explains how the special theory of relativity and classical mechanics are related - the first is a generalization of the second.
There is a wikibook on the topic
"Addition of speeds"
Physics. Give the definition of the speed of the body and the formula
Alexandra Romanova
The speed of a body is a vector quantity equal to the ratio of the path traveled by the body over a certain period of time to the value of this period of time. v=s/t.
1. Let the body move in a straight line and uniformly. Then its speed is represented by a constant value, does not change with time: v = const. The speed formula is v=v(const), where v(const) is a specific value.
2. Let the body move uniformly (uniformly accelerated or uniformly slowed down). As a rule, they only talk about uniformly accelerated motion, but in uniformly slowed down acceleration is negative. Acceleration is usually denoted by the letter a. Then the speed is expressed as a linear time dependence: v=v0+a·t, where v0 is the initial speed, a is the acceleration, t is the time.
3. Let the body move in a circle with a constant modulo speed. In this case, it has a centripetal acceleration a(c) directed towards the center of the circle. It is also called the normal acceleration a(n). Linear velocity and centripetal acceleration are related by the relation a=v²/R, where R is the radius of the circle along which the body is moving.
Alexei
speed - a vector physical quantity that characterizes the speed of movement and direction of movement of a material point in space relative to the selected reference system.
and the formula depends on the type of movement: if you have a uniformly accelerated movement, then v=v0+at. where a is the acceleration and t is the time. if you have uniform motion then s=vt, where v=s/t.
Tell me what is speed (definition) and a device for determining speed. (PHYSICS)
Tamara
Velocity is a quantitative characteristic of the motion of a body. Velocity characterizes the speed and direction of movement of the body at a given time. Speed is measured in m/s (meter per second). There are devices that can measure speed.
A speedometer (from English speed - speed and Greek metreo - I measure) is a device that shows the instantaneous speed of a car or locomotive.
A log, invented in 1577, is used to measure the speed of a ship. The unit of speed is the "knot", which is equal to one nautical mile per hour (approximately 1.8 km/h).
The first instrument for measuring wind speed was invented in 1667 by the Englishman Robert Hook. The device is called an anemometer (Greek anemos - wind, and metreo - I measure.
A device for measuring the speed of water flow is called a turntable.
Let's do an experiment. Install a dropper on the trolley (Fig. 11). Drops of a colored liquid fall from the dropper at regular intervals. If a load is attached to the trolley (as shown in Figure 11), then at a certain value of it, the distances between the traces left by drops on paper (when the trolley moves) may turn out to be equal. This means that the cart travels equal distances in equal intervals of time. Turning the dropper tap so that the drops fall more often, we repeat the experiment. The traces of drops in this case also turn out to be at equal distances from each other, although smaller than in the first experiment. And this means that the trolley travels the same paths in smaller equal intervals of time.
If a body travels the same paths in any equal intervals of time, then its motion is called uniform.
The speed of movement is characterized by a physical quantity called speed. The plane is known to be moving faster than a car, and an artificial Earth satellite is faster than an airplane.
Speed body at uniform motion shows how far the body travels per unit of time. For example, if in every hour a pedestrian travels 3 km and an airplane flies 900 km, then we say that the speed of the pedestrian is 3 km/h and the speed of the aircraft is 900 km/h.
If it is known that the same pedestrian travels 6 km every two hours, then in order to find out which path he travels in 1 hour, these 6 km should be divided by 2 hours. In this case, we again get 3 km / h.
So, to determine the speed of a body in uniform motion, it is necessary to divide the distance traveled by the body by the time of motion, i.e.
Let us denote all the quantities included in this expression in Latin letters:
s- path, v- speed, t- time.
Then the formula for finding the speed can be represented as follows:
In SI, the unit of speed is taken as the speed of such uniform movement, at which a moving body for 1 s is like a path equal to 1 m. This unit is denoted or 1 m / s (read "meter per second").
In practice, another unit of speed is often used: 1 km / h. Let's find the relationship between different units of speed. Since 1 km = 1000 m, and 1 h = 60 min = 3600 s, we can write:
Consider an example. Let it be required to express the speed of the aircraft, equal to 720 km/h, in meters per second. Converting kilometers to meters and hours to seconds, we get
With uniform motion, the numerical value of the speed does not change. If, for example, the speed of a body is 60 km/h, then this value will remain the same throughout the entire time of movement.
But, in addition to its numerical value, speed also has its direction. Therefore, in the figures, the speed of the body is depicted as an arrow (Fig. 12). The arrow indicates the direction of the speed (and hence the movement) of the body.
Quantities that have a direction in space are called vector quantities or simply vectors. Speed is a vector quantity. A vector quantity, as we shall see later, is also a force. On the other hand, such quantities as mass, path, volume, are not vectors: they have no direction in space and are characterized only by a numerical value.
Table 2 shows the values of some of the speeds found in nature.
table 2
Travel speeds, m/s
Not all motions listed in Table 2 are uniform. Only sound, light and radio waves, under certain conditions, propagate with constant speed. The velocities of other bodies change in the process of motion. Therefore, for them, the average or maximum values that can be achieved by these bodies are indicated.
Movements in which the speed of the body is different in different parts of the trajectory are called uneven.
Uneven movements characterize average speed. average speed of uneven motion is found in the same way as the speed of uniform motion, i.e., the path traveled by the body is divided by the time of motion: Only the value obtained in this case may not coincide with the speed of the body in certain sections of the trajectory. With uneven movement, the body in some areas has a lower speed, in others - a greater one. For example, a train leaving a station starts moving faster and faster. Approaching the station, he, on the contrary, slows down his movement.
Only with uniform motion, the speed of the body throughout the entire trajectory has a constant numerical value.
Knowing the speed and time of uniform motion of the body, it is possible to calculate the path traveled by the body. From formula (6.1) it follows that
(6.2)
So, to find the distance traveled with uniform motion, it is necessary to multiply the speed of the body by the time of motion.
If the path and speed are known, then the time of movement can be found. From formula (6.2) we obtain
(6.3)
So, to find the time of motion, you need to divide the distance traveled by the body by its speed.
1. What movement is called uniform? 2. What does the speed of uniform movement show? 3. How is speed determined in uniform motion? 4. How is the distance traveled if the speed and time of movement are known? 5. How is the time of movement if the path and speed of movement are known? 6. What movement is called uneven? 7. How should the conditions of the experiment shown in Figure 11 be changed so that the movement of the cart becomes uneven? How will the distances between the traces left by falling drops change in this case? 8. How is the average speed? 9. What quantities are called vector? How are they depicted in the pictures?
Experimental tasks. 1. Determine the average speed at which you run 100 m. 2. If you have a toy clockwork car at home, then, after taking the necessary measurements, find the average speed at which it moves. Record the results of measurements and calculations in a notebook.
This topic will be useful not only for high school students, but even for adults. In addition, the article will be of interest to parents who want to explain simple things from the natural sciences to their children. Among the very important topics is speed in physics.
Quite often, students cannot figure out how to solve problems, distinguish between the available types of speeds, and it is even more difficult to understand scientific definitions. Here we will consider everything in a more accessible language, so that everything is not only clear, but even interesting. But you still have to remember some things, because Technical science(physics and mathematics) require memorizing formulas, units of measurement and, of course, the meanings of symbols in each formula.
Where is it found?
To begin with, let's recall that this topic refers to such a section of physics as mechanics, subsection "Kinematics". In addition, the study of speed does not end here, it will be in the following sections:
- optics,
- vibrations and waves
- thermodynamics,
- quantum physics and so on.
Also, the concept of speed is found in chemistry, biology, geography, computer science. In physics, the topic "velocity" occurs most often and is studied in depth.
In addition, this word is used in everyday life by all of us, especially among motorists, drivers transport technology. Even experienced cooks sometimes use a phrase such as "beat the egg whites with a mixer at medium speed."
What is speed?
Velocity in physics is a kinematic quantity. It means the distance traveled by a body in a certain period of time. Let's say a young man moves from home to a store, covering two hundred meters in one minute. On the contrary, his old grandmother will pass by the same route in six minutes in small steps. That is, the guy moves much faster than his elderly relative, as he develops speed much more, taking very fast long steps.
The same is true for a car: one car goes faster and the other slower because the speeds are different. Later we will consider numerous examples related to this concept.
Formula
At the lesson at school, the speed formula in physics is necessarily considered in order to make it convenient to solve problems.
- V is, respectively, the speed of movement;
- S is the distance covered by the body when moving from one point in space to another;
- t - travel time.
You should remember the formula, because it will come in handy in the future when solving many problems and not only. For example, you might be wondering how fast you can get from home to work or school. But you can find out the distance in advance using a map on your smartphone or computer, or using a paper version, knowing the scale and having a ruler with you. Next, you note the time before you start moving. Arriving at your destination, see how many minutes or hours it took to pass without stopping.
What is measured?
Speed is most often measured using the SI system of units. Below are not only units, but also examples of where they are applied:
- km/h (kilometer per hour) - transport;
- m/s (meter per second) - wind;
- km/s (kilometer per second) - space objects, rockets;
- mm/h (millimeter per hour) - liquids.
Let's first figure out where the fractional line came from and why the unit of measurement is just that. Pay attention to the physics formula for speed. What do you see? The numerator is S (distance, path). How is distance measured? In kilometers, meters, millimeters. In the denominator, respectively, t (time) - hours, minutes, seconds. Hence, the units of measurement of the quantity are exactly the same as presented at the beginning of this section.
Let's consolidate with you the study of the velocity formula in physics as follows: what distance will the body overcome in a specific period of time? For example, a person walks 5 kilometers in 1 hour. Total: the speed of a person is 5 km / h.
What does it depend on?
Often teachers ask students the question: "What determines the speed?". Students often get lost and don't know what to say. In fact, everything is very simple. Just look at the formula for a hint to pop up. The speed of a body in physics depends on the time of motion and distance. If at least one of these parameters is unknown, it will be impossible to solve the problem. In addition, other types of speeds can be found in the example, which will be discussed in the following sections of this article.
In many tasks in kinematics, you have to build dependency graphs, where the X-axis is time, and the Y-axis is distance, path. From such images, one can easily assess the nature of the speed of movement. It is worth noting that in many professions related to transport, electric machines often use graphics. For example, on the railroad.
At the right time, measure the speed
There is another topic that scares middle school students - instantaneous speed. In physics, this concept occurs as a definition of the magnitude of speed in an instantaneous period of time.
Let's look at a simple example: the driver is driving a train, his assistant is watching the speed from time to time. You can see it in the distance. You should check how fast the train is moving right now. The driver's assistant reports at 4:00 pm that the speed is 117 km/h. This is the instantaneous speed recorded exactly at 4 pm. Three minutes later, the speed was 98 km/h. This is also the instantaneous speed relative to 16 hours 03 minutes.
Start of movement
Without the initial speed, physics does not represent almost any movement of transport equipment. What is this parameter? This is the speed at which the object starts moving. Let's say a car cannot start moving instantly at a speed of 50 km/h. She needs to speed up. When the driver presses the pedal, the car begins to move smoothly, for example, at a speed of 5 km/h first, then gradually 10 km/h, 20 km/h and so on (5 km/h is the initial speed).
Of course, you can make abrupt start, which happens to runners-athletes when hitting a tennis ball with a racket, but still there is always an initial velocity. By our standards, only the stars, planets and satellites of our Galaxy do not have it, since we do not know when the movement began and how. Indeed, until death, space objects cannot stop, they are always in motion.
uniform speed
Speed in physics is a combination of individual phenomena and characteristics. There are also uniform and non-uniform motion, curvilinear and rectilinear. Let's give an example: a person walks along a straight road with the same speed, overcoming a distance of 100 meters from point A to point B.
On the one hand, this can be called rectilinear and uniform speed. But if you attach very accurate speed and route sensors to a person, you can see that there is still a difference. Uneven speed is when the speed changes regularly or constantly.
In everyday life and technology
The speed of motion in physics exists everywhere. Even microorganisms move, albeit at a very slow speed. It is worth noting that there is rotation, which is also characterized by speed, but has a unit of measurement - rpm (revolutions per minute). For example, the speed of rotation of the drum in washing machine. This unit measurement is used wherever there are mechanisms and machines (engines, motors).
In geography and chemistry
Even water has a speed of movement. Physics is just a subsidiary science in the field of processes occurring in nature. For example, wind speed, waves in the sea - all this is measured by the usual physical parameters, quantities.
Surely, many of you are familiar with the phrase "the rate of a chemical reaction." Only in chemistry does it have a different meaning, since it means how long this or that process will take place. For example, potassium permanganate will dissolve faster in water if you shake the vessel.
Stealth Speed
There are invisible phenomena. For example, we cannot see how particles of light, various radiations move, how sound propagates. But if there were no movement of their particles, then none of these phenomena would exist in nature.
Computer science
Almost every modern person is faced with the concept of "speed" while working on a computer:
- Internet speed;
- page loading speed;
- processor loading speed and so on.
There are a huge number of examples of the speed of movement in physics.
Reading the article carefully, you got acquainted with the concept of speed, learned what it is. Let this material help you study the "Mechanics" section in depth, show interest in it and overcome fear when answering in the lessons. After all, speed in physics is a common concept that is easy to remember.
Speed is a quantitative characteristic of the movement of the body.
average speed is a physical quantity equal to the ratio of the point displacement vector to the time interval Δt during which this displacement occurred. The direction of the average speed vector coincides with the direction of the displacement vector The average speed is determined by the formula:
Instant Speed, that is, the speed at a given moment of time is a physical quantity equal to the limit to which the average speed tends with an infinite decrease in the time interval Δt:
In other words, the instantaneous speed at a given moment of time is the ratio of a very small movement to a very small period of time during which this movement occurred.
The instantaneous velocity vector is directed tangentially to the trajectory of the body (Fig. 1.6).
Rice. 1.6. Instantaneous velocity vector.
In the SI system, speed is measured in meters per second, that is, the unit of speed is considered to be the speed of such uniform rectilinear motion, in which in one second the body travels a distance of one meter. The unit of speed is denoted m/s. Often speed is measured in other units. For example, when measuring the speed of a car, train, etc. The commonly used unit of measure is kilometers per hour:
1 km/h = 1000 m / 3600 s = 1 m / 3.6 s
1 m/s = 3600 km / 1000 h = 3.6 km/h
Addition of speeds
The speed of the body in various systems reference connects the classical law of addition of speeds.
body speed relative to fixed frame of reference is equal to the sum of the velocities of the body in moving frame of reference and the most mobile frame of reference relative to the fixed one.
For example, passenger train is moving along the railroad at a speed of 60 km/h. A person is walking along the carriage of this train at a speed of 5 km/h. If we consider the railway to be motionless and take it as a frame of reference, then the speed of a person relative to the frame of reference (that is, relative to railway), will be equal to the addition of the speeds of the train and the person, that is
60 + 5 = 65 if the person is walking in the same direction as the train
60 - 5 = 55 if the person and the train are moving in different directions
However, this is only true if the person and the train are moving along the same line. If a person moves at an angle, then this angle will have to be taken into account, remembering that speed is vector quantity.
Now let's look at the example described above in more detail - with details and pictures.
So, in our case, the railway is fixed frame of reference. The train that is moving along this road is moving frame of reference. The car on which the person is walking is part of the train.
Let's associate the XOY coordinate system with the fixed reference system (Fig. 1.7), and the X P O P Y P coordinate system with the moving reference system (see also the Reference System section). And now let's try to find the speed of a person relative to a fixed frame of reference, that is, relative to the railway.
This displacement addition law. In our example, the movement of a person relative to the railway is equal to the sum of the movements of a person relative to the wagon and the wagon relative to the railway.
Rice. 1.7. The law of addition of displacements.
This is the law speed addition:
The speed of the body relative to the fixed frame of reference is equal to the sum of the velocities of the body in the moving frame of reference and the speed of the moving frame itself relative to the fixed one.
Who do you think moves faster agronomist Vasechkin, Renault car Or a Boeing plane? Which of them will get from Moscow to Krasnodar faster? The answer is obvious. Renault is faster than Vasechkin, but slower than Boeing.
That is, we not only know how different objects move, but we can also compare their speeds. What is speed in physics? How to find the speed of a body, and what are the units of speed?
Speed in physics: how to find speed?
In the 7th grade, the concept of speed is introduced in physics lessons. Without a doubt, all schoolchildren by this moment are already familiar with this word and imagine what it means.
- They also know that speed is measured in km/h and is denoted by the letter V.
But it is unlikely that they can coherently explain what speed is in physics, what are the units of speed. That is why this seemingly simple concept requires explanation and analysis.
In physics, the speed of movement of Vasechkin, Renault and Boeing called their speed. And this speed characterizes which path each of the participants of this journey overcomes per unit of time. And if in flight we will overcome the distance of 1350 kilometers between Moscow and Krasnodar in two hours, by car we will need no less than 15 hours, then on foot the reckless Vasechkin will be able to walk his entire vacation at a brisk pace and arrive at the place only in order to to kiss my mother-in-law, to eat pancakes and to catch a plane to Moscow in order to be in time for work on Monday.
Accordingly, per unit of time per hour, the plane will fly 670 kilometers, the car will travel 90 kilometers, and the tourist Vasechkin will wave as many as five kilometers of the road. And then they say that the speed of an airplane is 670 kilometers per hour, a car is 90 kilometers per hour, and a pedestrian is 5 kilometers per hour. That is, the speed is determined by dividing the distance traveled per unit of time by an hour, a minute, or a second.
Speed units
In practice, units such as km / h, m / s and some others are used. They denote speed with the letter v, distance with the letter s, and time with the letter t. Formula for finding speed in physics looks like that:
- V = s / t,
Where s is the distance traveled
t is the time taken to overcome this path
And if we need to recalculate the speed not in kilometers per hour, but in meters per second, then the recalculation takes place as follows. Since 1 km = 1000 m, and 1 h = 60 min = 3600 s, we can write: 1 km / h = (1000 m) / (3600 s). And then the speed of the aircraft will be equal to: 670 km / h \u003d 670 × (1000 m) / (3600 s) \u003d 186 m / s
In addition to its numerical value, the speed also has a direction, therefore, in the figures, the speed is indicated by an arrow and is called a vector quantity.
Average speed in physics
Let's note one more point. In our example, the driver of the car was driving at a speed of 90 km/h. On the highway, he could drive evenly at that speed for a long time. But passing through different cities along the way, he either stopped at traffic lights, crawled in traffic jams, or picked up a good speed in short bursts.
Those. his speed on different parts of the path was uneven. In this case, the concept of average speed is introduced. The average speed in physics is denoted by V _av and is considered the same as the speed with uniform motion. Just take the total travel distance and divide by the total time.
