energy from one form into another form of the process. Acting of the two essential factors: the force acting on a body and objects in the direction of force by the distance. The definition of classical mechanics: when a force acting on a body, and make objects in the direction of force by some distance, say mechanics force on the object to do this successfully.
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Introduction to the 2, displacement and distance 3, the power has positive and negative points 4, 5 work done variable force, acting with the choice of the reference 6. Current acting 7. Current work (electric) Introduction to the different nature and different forms of energy form corresponding to the movement: the movement of objects with mechanical energy, the molecules with internal energy, charge movement with power, with the atomic nuclei within the movement and so on. Between different forms of energy can be transformed into each other: mechanical energy; current work done by the electric wire can convert electrical energy into heat energy, and so on. These examples illustrate the different forms of energies can be transformed into each other, and the acting is done through the transformation process. In introducing the concept of power before the physical advised to literally explain the Credit, with the Results, results,UGG Boots, results of means, such as a multiplier, you're done 3. Technology and technical training, such as singing, basic skills, and so on. The main emphasis in the power of physics in the The introduction of the concept of why we introduce the concept of power? Describe the movement of objects and the relationship between the force we have Newton's Second Law, no longer seems superfluous, and then give an example so that we can think about - people cart. At this point the imposition of a car by force F, in overcoming the friction, how will the car after the campaign? The answer is the car began to accelerate forward movement from the rest, in other words, the car's motion state changes, over a period of time after the car's speed from zero to a certain speed, speed, reflects changes in the size of the force F on the car The effect, but we have to ask the force F on the effect of the car that changes the size of the car motion state (here the size variation of speed) in addition to the other with force F, but also what factors? Is the role of time and force the car's displacement of these two factors, the role of force aside time for the time being (which will be part of the impulse Theorem: force the cumulative effect of time on the object), take a look at the car's displacement of the factors that can so that if the car's displacement is zero, then the force F on the effect of the car will be zero, indicating that the force F while the effect of the car and the force F and displacement, force alone can not describe F or displacement force F on The effect of the car, in fact, Newton's second law F = ma force F only shows the instantaneous relationship between the role of the object, the external force F acting on the object on the object will produce acceleration a, the state of motion of objects will change, but objects state of motion can change, that the external force F on the effect of the object, but also on the force F the displacement of objects under S, we have the role of external forces on the object for some distance and the effect, known as the force of the cumulative effect of space objects Therefore, we need to define a physical quantity to describe the force on the cumulative effect of space objects, because of this physical quantity is used to describe the effect of force F, so we use the Chinese characters above, which is borrowed Chinese characters This means that the force F on the objects have a role in the results, we say that force has done a power of objects, that is, the state of motion of an object or objects corresponding changes in the energy, and vice versa. Derived formula: If the power that the size of the W, F, said the size of force, S is the size of the displacement, according to the definition of power, power is used to describe the effect of force F, obviously, the greater the force, the greater the displacement The effect of force F is more obvious, that the greater the value of W, which shows that, W and F and S should become a positive relationship, that is, W = FS, taking into account the force and displacement are vectors, there are directions, force and displacement direction is not how to do the same? An example can illustrate this situation should force along the displacement direction and the direction perpendicular to the displacement decomposition, as in the direction perpendicular to the displacement of an object does not shift, so the direction perpendicular to the displacement of the force is not acting, that is, for power The effect of the object made no contribution, so you can arrive at W = FS cosα (α is the direction of force F and displacement angle between the direction of S), force and direction of the force on an object in motion through the power of two is necessary factors, are indispensable. Pay particular attention to objects by multiple force,UGG Boots, you can seek together first and then seek work done together, or you can find a pitch made for each function, then each made a pitch function algebra come together to work done by the sum, which means that when we calculate the size of power is the pursuit of which must be clear which of a force or power of work done. Points discussed several cases the physical meaning of a power, an object by external force, but stationary. For example, a person carrying a bucket of water standing still, or by pushing a stationary car but did not push this bucket of water or a car because of the displacement S = 0, according to W = FS cosα, this person does work W = 0, even though this person spent a lot of effort, but not acting, from this point to understand the physical meaning of power, because power is used to describe the role of force F on the space object cumulative effect, because the role of the force F before and after the state of motion of objects or objects without corresponding changes in energy, and that bucket of water or that car is still in place, the force F on that bucket of water or the effect that car is zero, that is, that bucket of water on the force F Or that car is not acting, W = 0. This is with people often say a measure, than the 2, displacement and distance W = FS cosα S is the displacement, with the distance to distinguish. For example, a person brought an object from the ground and back into place, then the gravitational power is made how much? Because the object and back into place, and the size of the object displacement is zero, so W = 0. Note here the object is not zero distance traversed. Although the objects have changed the state of motion (or energy state), but eventually the object back to the original state of motion, the role of gravity on objects, the cumulative effect of the space is zero, no change in the state of motion of objects, that is not acting on the object. Note, however, there is a particularly confusing: a car to go back and forth along a straight line, the size of the displacement is zero, then according to the formula W = FS cosα power does a car engine power is not zero? From experience, we can determine the answer is no! Wrong there? Should be noted that the direction of vehicle engine power and return the car to change them, we should be broken down into the car's displacement to the displacement of the displacement and return two (note that co-displacement is zero), sub-application seeking the formula W = FS cosα Power work done on the car, and then were successful on two shifts and demand algebra, you will find power the car made power is not zero, indicating that application of the formula W = FS cosα computing power of the size, special Note F in the direction of the displacement process should remain the same (in fact, size can not be changed), the above mentioned examples of objects and back into the place, in the process of displacement size and direction of gravity remains unchanged. 3, there are positive and negative reactive power is divided into scalar, there is no direction, but there are positive and negative points, when α> 90 ° when, cosα <0, so W <0, this is the force F to do negative work situation. At this point the direction of force F and the movement of objects roughly the opposite direction, force F is the force impeding the movement of objects (when the force F, also known as resistance), then we say that the force F on the object to do negative work, W to take negative values; or moving object to overcome the resistance to do the power, then take the absolute value of W. When α <90 ° when, cosα> 0, so W> 0, this is the force F to do positive work situation. At this point the direction of force F and the movement of objects roughly the same direction, force F is the force to promote the movement of objects (in this case, also known as dynamic force F), when α = 90 ° when, cosα = 0, so W = 0,UGG Boots, this shows the direction perpendicular to the force and displacement is not acting. For example, the level of an object surface in rough uniform glide, power and friction are doing positive work and negative work, and supportive work done by the gravity is zero. From Newton's second law point of view, the direction of the object displacement in the same direction with the force to accelerate an object, the object displacement in the opposite direction with the direction of the force that objects slow down, perpendicular to the displacement direction of the force for the displacement of an object has no effect on the acceleration, from power point of view, corresponding to positive power, negative power and zero. 4, variable force power do we know the formula W = FS F only do work during the same size and direction of the case is correct, then the process of acting or the direction of F changes the size of the case, how to calculate the size of power? In this case, the displacement should be broken down into many small displacement S dS, dS can be similar in that each the size and direction of F is constant, so F dS in this still on the work done dW expressed as dW = FdS, force in the work done on each dS dW can add up throughout the displacement of the F on the work done by the S W, which use the knowledge of calculus. 5, acting with the choice of the reference as W = FS, S the size of the displacement and the choice of the reference, so the size will power and choice of the reference. For example, a car traveling on the road, if you choose to do the ground reference, and known to the engine power is F, then the car after a displacement of S, the engine of the car made power W = FS ≠ 0, that is, from the ground see, the car motion state changes, power to the cumulative effect of the car space is not zero; If you select car make reference, the car's displacement S is zero, so the car does the engine power W = FS = 0, view from the car, the car did not change the state of motion, power on the cumulative effect of the space vehicle to zero, indicating that the choice of doing work with the relevant reference. But no matter what point of reference, the energy consumed by the engine power is the ultimate form of transformation. So, whether in accordance with the above statement can be said that if the automobile as the reference, the energy consumption of the engine would not it? 6. Current acting current acting process is converted into other forms of energy can process. How much work do current, there is much energy into other forms of energy. Electric power of the basic formula: the current through a conductor made of this power is equal to the voltage across the conductor, the current through the conductor and through time into the plot. That is, W = UIt. In international units, the energy unit is Joule electric power, with the notation J said; life of popular unit is kilowatt-hour (KW.h), 1kw.h = 3.6 × 1000000J outstanding cyclist prolonged exercise power of about 70W, short-term movement of the power up to 1kW Shanghai Santana brand cars power of about 66kW of power carts for a long time about 450W7. Current work (electric) current use of certain electrical appliances acting, producing electric, the service of humanity! Electric sign of Q in J electric formula: Q = I ^ 2 Rt = IUt (square of the current × resistance × current × voltage power-on time is power × time) extended reading: 1http://zhidao.baidu. com / books
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