Daily experience shows that the property of the body can be moved, and moved to stop.We are always something to do around the world bustles, sunshine ... But where in humans, animals, and nature in general have taken the strength to do this work?Whether mechanical motion disappears without a trace?Will the move one body movement without changing the other?All this will be discussed in this article.
energy concept for the engine, which gives the movement of cars, tractors, locomotives, airplanes need fuel, which is a source of energy.Electric motors give the movement of the machine by means of electricity.Due to the energy of water falling from a height, turn hydraulic turbine connected to the electrical machines, producing an electric current.Man to exist and work, also need energy.They say that in order to carry out in order some work requires energy.What is energy?
- Observation 1. Lift the ground ball.While he is in a state of tranquility, the mechanical work is not performed.Let him go.By gravity the ball falls to the ground from a certain height.During the fall of the ball performed mechanical work.
- Observation 2. somknite spring, fix its thread and put little weight on the spring.Ablaze thread spring straighten and raise little weight on some height. Spring performed mechanical work.
- Observation 3. On the trolley will fix the rod with a block at the end.Through block perekinem thread one end of which is wound around the axis of the truck, and the other hanging sinker.Let go of the sinker.Under the action of gravity it would fall down and give a trolley motion. weights performed mechanical work.
After analyzing all of the above observations, we can conclude that if the body or several bodies during the interaction perform mechanical work, then we say that they have a mechanical power or energy.
energy concept
energy (from the Greek. word energy - activities) - is a physical quantity that characterizes the body's ability to perform the work.The unit of energy, as well as work in the SI system is one joule (1 J).In a letter to the energy denoted by the letter E .From the above experiments it is evident that the body performs work when the transitions from one state to another.The energy of the body with the changes (decreases), and the mechanical work performed by the body is the result of a change in its mechanical power.
Types of mechanical energy.The concept of potential energy
There are 2 types of mechanical energy: potential and kinetic.Now a closer look at the potential energy.
potential energy (PE) - is the energy determined by the relative position of the bodies that interact or parts of the body itself.Since every body and earth attract each other, that is, interact, PE body raised above the ground will depend on the height of lifting h .The higher the body is raised, the more his PE.It was established experimentally that PE not only depends on the altitude at which it is raised, and the body weight.If the bodies are raised to the same height, the body having a larger mass will have a greater and PE.The formula of this energy is as follows: Ep = mgh, where Ep - is potential energy, m - weight, g = 9,81 N / kg, h - height.
potential energy of the spring
potential energy elastically deformed body is called physical quantity Ep, that when you change the speed of forward movement by the forces of elasticity decreases by exactly as much as the kinetic energy increases.Springs (and other elastically deformed body) have a PE, which is equal to half the product of their rigidity k the square of the strain: x = kx2: 2.
kinetic energy: the formula and definition
Sometimes the value of mechanical work can be seenwithout the use of the concepts of power and movement, focusing on the fact that the work represents the change in the body's energy.All that we may need - is the mass of a body and its initial and final speed that will lead us to the kinetic energy.The kinetic energy (KE) - the energy attributable to the body as a result of its own motion.
kinetic energy is wind, it is used to impart motion wind turbines.Driven by air masses exert pressure on the ramps of the wings of wind turbines and make them turn around.The rotary motion transmission systems using the transfer mechanism, performing some work.Driven by the water, turns the turbine power, loses some of its EC, doing the work.Flying high in the sky plane, in addition to PE, a CE.If the body is in a state of rest, that is, its ground speed is zero, and its CE relative to the earth is zero.It was established experimentally that the greater weight of the body and the speed at which it moves, the more it TBE.The formula of the kinetic energy of the translational motion in the following mathematical expression:
Where To - kinetic energy, m - body weight, v - speed.
change in kinetic energy
Since the velocity of the body is variable depending on the choice of the reference frame, the value of FE body also depends on the choice.The change of kinetic energy (IKE) body is due to the action of an external force on the body F .A physical quantity , which is IKE ΔEk body due to the action of force on him F, called the operation: A = ΔEk. If a body that moves with speed v 1 , the force F , coinciding with the direction, the speed of movement of the body will increase the time interval t to a certain value v 2 .This IKE well:
Where m - body weight; d - traversed path of the body; Vf1 = (V2 - V1);Vf2 = (V2 + V1);a = F: m .It is for this formula is calculated, how much kinetic energy is changed.The formula can also be interpreted as follows: ΔEk = Flcos ά , where cosά is the angle between the vectors of force F and speed V .
average kinetic energy
Kinetic energy is the energy determined by the speed of the different points that belong to this system.However, be aware that it is necessary to distinguish between two energy characterize different types of movement: translational and rotational.The average kinetic energy (SKE) in this case is the average difference between the total energy of the whole system and its power of mind, that is, in fact, its value - is the average value of the potential energy.The formula of the average kinetic energy of the following:
where k - is Boltzmann constant;T - temperature.It is this equation is the basis of the molecular-kinetic theory.
average kinetic energy of gas molecules
Numerous experiments it was found that the average kinetic energy of gas molecules in the forward movement at a given temperature is the same and does not depend on the type of gas.Furthermore, it was also found that by heating the gas at 1 ° SKE is incremented by one and the same value.To tell more precisely, the value is: ΔEk = 2.07 x 10-23Dzh / C. order to calculate what is the average kinetic energy of gas molecules in the forward movement, you must, in addition to this relative value, even know at least one absolute value of the energy of translational motion.In physics to accurately determine these values for a wide range of temperatures.For example, at a temperature t = 500 ° C kinetic energy of the translational motion of the molecule Ek = 1600 x 10-23Dzh. Knowing the value 2 ( ΔEk and Ek), how we can calculate the energy of the translational motion of the molecules at a given temperature, and to solve the inverse problem - to determine the temperature at the given values of energy.
Finally, we can conclude that the average kinetic energy of the molecules, the formula of which is shown above, it depends only on the absolute temperature (and for every state of matter).
law of conservation of total mechanical energy
study of the motion of bodies under the action of gravity and the elastic forces showed that there is a physical quantity, which is called potential energy E ;it depends on the body frame, and its change is equated IKE, which is taken with the opposite sign: Δ E = - ΔEk. Thus, the amount of change of CE and PE body that interact with the gravitational forces and the elasticity is equal to 0 : Δ En + ΔEk = 0. forces, which depend only on the coordinates of the body, called conservative. attractive forces and elastic forces are conservative.The sum of the kinetic and potential energies of the body is full of mechanical energy: En + Ek = E
This fact, which has been proven the most accurate experiments,
called the law of conservation of mechanical energy .If the body interact with the forces that are dependent on the relative velocity, the mechanical energy of the system of interacting bodies is not saved.An example of this type of forces, which are called non-conservative , are friction.If the body of a frictional force, it is necessary to overcome them to expend energy that is part of it is used to perform work against the forces of friction.However, violation of the law of conservation of energy is only imaginary, because it is a special case of the general law of conservation and transformation of energy. energy bodies never disappears and reappears: it only converted from one form to another.This law of nature is very important, it is done everywhere.It is also sometimes referred to as the general law of conservation and transformation of energy.
connection between the internal energy of the body, the kinetic and potential energies
internal energy (U) of the body - it is his full energy of the body minus the CE body as a whole and its PE in the external field strength.From this we can conclude that the internal energy is composed of the random motion of the molecules of CE, PE, and the interaction between them vnutremolekulyarnoy energy.Internal energy - a single-valued function of the state, which means the following: if the system is in this state, its internal energy takes its inherent values, regardless of what happened before.
Relativism
When the speed of the body close to the speed of light, the kinetic energy is found by the following formula:
kinetic energy of the body, the formula of which was written above, it may also be calculated on the following principle:
Examples of problems in finding a kineticEnergy
1. Compare the kinetic energy of the ball weight 9 g, flying at a speed of 300 m / s, and a person weighing 60 kg, traveling at a speed of 18 km / h.
So, what we have been given: m1 = 0,009 kg;V1 = 300 m / s;m2 = 60 kg, V2 = 5 m / s.
Solution:
- kinetic energy (formula): Ek = mv2: 2.
- We have all the data for the calculation and, therefore, we find Ek for man and the ball.
- Ek1 = (0.009 kg s (300 m / s) 2) 2 = 405 J;
- Ek2 = (60 kg x (5 m / s) 2) 2 = 750 J.
- Ek1 & lt; Ek2.
Answer: The kinetic energy of the ball is smaller than a person.
2. A body with a mass of 10 kg has been raised to a height of 10 meters, after which he was released.What CE it will have at a height of 5 m?Air resistance is allowed to be neglected.
So, what we have been given: m = 10 kg;h = 10 m; h 1 = 5 m;g = 9,81 N / kg. Ek1 -?
Solution:
- body of certain mass, raised to a certain height, has a potential energy: Ep = mgh.If the body falls, it is at a certain height h1 will have a sweat.energy Ep = mgh1 and kin.Ek1 energy.To properly found the kinetic energy of the formula, which has been shown above, does not work and therefore solve the problem according to the following algorithm.
- In this step, we use the law of conservation of energy and write: Ep1 + Ek1 n = E.
- Then Ek1 = E n - Ep1 = mgh - mgh 1 = mg (h-h1).
- Substituting our values into the formula, we get: Ek1 = 9.81 x 10 (10-5) = 490.5 J.
Answer: Ek1 = 490.5 J.
3. The flywheel with a mass m and radius R, wrapped around an axis passing through its center.The angular velocity of the flywheel wrapping - ω .In order to stop the flywheel to its rim is pressed against the brake shoe acting on it with force Ftreniya .How many revolutions will make the flywheel to a stop?Take into account that the weight of the flywheel is centered on the rim.
So, what we have been given: m; R; ω; Ftreniya.N -?
Solution:
- In solving the problem, we assume momentum flywheel turns like a thin uniform hoop with radius R and weight m, which turns into an angular velocity ω.
- The kinetic energy of the body is equal to: Ek = (J ω 2) 2, where J = m R 2.
- Flywheel stop, provided that all of its TBE spent on work to overcome the frictional force Ftreniya, arising between the brake pad and the rim: Ek = Ftreniya * s, where
