What is work, they know everything.Even children work in kindergarten - kids.However, conventional, domestic representation is not the same as the concept of mechanical work in physics.For example, a man stands and holds a bag.In the usual sense, he does the work of holding the load.However, from the point of view of physics, nothing like he did not commit.What was going on?
appearances such questions, it's time to recall the definition.As for the force, and under the influence of a body is moved, then the mechanical work.This value is proportional to the path traveled by the body and the applied force.There is more dependence on the direction of application of force and the direction of motion of the body.
Therefore, we have introduced such a thing as mechanical work.Physics defines it as the product of force and displacement times the cosine of the angle value present in the general case therebetween.As an example, consider a few cases, that will allow to know better what is meant thereby.
When the mechanical work is not done?Worth truck, we push, and he is not moving.Force is applied, as no movement.Performs work equal to zero.And here's another example - the mother carries a child in a wheelchair, in which case the work is done, the force is applied, the carriage is moved.The difference in the two cases described in the presence of motion.And accordingly, the work is performed (for example with a sidecar), or not (an example of a truck).
Another case - the boy on a bicycle and dispersed quietly rolling on the track, pedal not cool.Work in process?No, although the movement is there, but there is no force applied, the movement is carried out mechanically.
Another example - a horse driven cart, the driver is sitting on it.Whether committed work?Moving is, force is applied (weight of the driver acts on the cart), but the work is not performed.The angle between the direction of movement and direction of the force is 90 degrees, and the cosine of 90 ° is equal to zero.
These examples allow us to understand that the mechanical work - it's not just the product of two values.It should also consider how these values are sent.If the direction of travel and direction of the force of the same, the result will be positive if the direction of movement is opposite to the direction of application of force, the result will be negative (for example, work done by the frictional force when moving cargo).
also need to take into account that the force acting on the body may be the resultant of several forces.If so, then the work of all the forces applied to the body is equal to the work done by the resultant force.Work is measured in joules.One joule is the work that makes the force of one newton moving body at one meter.
From these examples, you can make a very interesting conclusion.When we looked at the charioteer on a cart, it determined that it does not make work.The work is done in a horizontal plane, because that is where the transfer is made.But the situation will change slightly when we consider the pedestrian.
When walking the center of gravity of a person does not remain immobile, it is moving in the vertical plane and therefore does work.Since the movement is directed against gravity, the operation will take place against the direction of gravity.Let the movement of small but long walks body will have to make extra work.So correct gait reducing the extra work and reduces fatigue.
analyzing a few simple life situations, selected as examples, and using the knowledge that is the mechanical work, we examined the basic situation of its manifestations, as well as when and how the work is done.We determined that such a thing as a life and work in physics has a different character.And established by applying physical laws that abnormal gait causes additional fatigue.
