Ohm formula for a section of an electrical circuit. All types of Ohm's laws
What does it mean?
In physics, “mechanical work” is the work of some force (gravity, elasticity, friction, etc.) on a body, as a result of which the body moves.
Often the word “mechanical” is simply not written.
Sometimes you can come across the expression “the body has done work,” which in principle means “the force acting on the body has done work.”
I think - I'm working.
I'm going - I'm working too.
Where is the mechanical work here?
If a body moves under the influence of a force, then mechanical work is performed.
They say that the body does work.
Or more precisely, it will be like this: the work is done by the force acting on the body.
Work characterizes the result of a force.
The forces acting on a person perform on him mechanical work, and as a result of the action of these forces, a person moves.
Work is a physical quantity equal to the product of the force acting on a body and the path made by the body under the influence of a force in the direction of this force.
A - mechanical work,
F - strength,
S - distance traveled.
Work is done, if 2 conditions are met simultaneously: a force acts on the body and it
moves in the direction of the force.
No work is done(i.e. equal to 0), if:
1. The force acts, but the body does not move.
For example: we exert force on a stone, but cannot move it.
2. The body moves, and the force is zero, or all forces are compensated (i.e., the resultant of these forces is 0).
For example: when moving by inertia, no work is done.
3. The direction of the force and the direction of movement of the body are mutually perpendicular.
For example: when a train moves horizontally, gravity does no work.
Work can be positive and negative
1. If the direction of the force and the direction of motion of the body coincide, positive work is done.
For example: the force of gravity, acting on a drop of water falling down, does positive work.
2. If the direction of force and movement of the body is opposite, negative work is done.
For example: the force of gravity acting on a rising balloon does negative work.
If several forces act on a body, then the total work done by all forces is equal to the work done by the resulting force.
Units of work
In honor of the English scientist D. Joule, the unit of work was named 1 Joule.
IN international system units (SI):
[A] = J = N m
1J = 1N 1m
Mechanical work is equal to 1 J if, under the influence of a force of 1 N, a body moves 1 m in the direction of this force.
When flying from thumb man's hands on the index
the mosquito does work - 0.000 000 000 000 000 000 000 000 001 J.
The human heart performs approximately 1 J of work per contraction, which corresponds to the work done when lifting a load weighing 10 kg to a height of 1 cm.
GET TO WORK, FRIENDS!
The horse pulls the cart with some force, let's denote it F traction. Grandfather, sitting on the cart, presses on it with some force. Let's denote it F pressure The cart moves along the direction of the horse's traction force (to the right), but in the direction of the grandfather's pressure force (downward) the cart does not move. That's why in physics they say that F traction does work on the cart, and F the pressure does not do work on the cart.
So, work of force on the body or mechanical work– a physical quantity whose modulus is equal to the product of the force and the path traveled by the body along the direction of action of this force s:
In honor of the English scientist D. Joule, the unit of mechanical work was named 1 joule(according to the formula, 1 J = 1 N m).
If a certain force acts on the body in question, then some body acts on it. That's why the work of force on the body and the work of the body on the body are complete synonyms. However, the work of the first body on the second and the work of the second body on the first are partial synonyms, since the moduli of these works are always equal, and their signs are always opposite. That is why there is a “±” sign in the formula. Let's discuss the signs of work in more detail.
Numerical values of force and path are always non-negative quantities. In contrast, mechanical work can have both positive and negative signs. If the direction of the force coincides with the direction of motion of the body, then the work done by the force is considered positive. If the direction of force is opposite to the direction of motion of the body, the work done by a force is considered negative(we take “–” from the “±” formula). If the direction of motion of the body is perpendicular to the direction of the force, then such a force does not do any work, that is, A = 0.
Consider three illustrations of three aspects of mechanical work.
Doing work by force may look different from the perspective of different observers. Let's consider an example: a girl rides up in an elevator. Does it perform mechanical work? A girl can do work only on those bodies that are acted upon by force. There is only one such body - the elevator cabin, since the girl presses on its floor with her weight. Now we need to find out whether the cabin goes a certain way. Let's consider two options: with a stationary and moving observer.
Let the observer boy sit on the ground first. In relation to it, the elevator car moves upward and passes a certain distance. The girl’s weight is directed in the opposite direction - down, therefore, the girl performs negative mechanical work on the cabin: A dev< 0. Вообразим, что мальчик-наблюдатель пересел внутрь кабины движущегося лифта. Как и ранее, вес девочки действует на пол кабины. Но теперь по отношению к такому наблюдателю кабина лифта не движется. Поэтому с точки зрения наблюдателя в кабине лифта девочка не совершает механическую работу: A dev = 0.
One of the most important concepts in mechanics is work of force .
Work of force
All physical bodies in the world around us are set in motion by force. If a moving body in the same or opposite direction is acted upon by a force or several forces from one or more bodies, then it is said that work is being done .
That is, mechanical work is performed by a force acting on the body. Thus, the traction force of an electric locomotive sets the entire train in motion, thereby performing mechanical work. The bicycle is driven by the muscular power of the cyclist's legs. Consequently, this force also does mechanical work.
In physics work of force call a physical quantity equal to the product of the force modulus, the displacement modulus of the point of application of the force and the cosine of the angle between the force and displacement vectors.
A = F s cos (F, s) ,
Where F force module,
s – travel module .
Work is always done if the angle between the winds of force and displacement is not zero. If the force acts in the direction opposite direction movement, the amount of work has a negative value.
No work is done if no forces act on the body, or if the angle between the applied force and the direction of movement is 90 o (cos 90 o = 0).
If a horse pulls a cart, then the horse's muscular force, or the traction force directed along the direction of the cart's movement, does work. But the force of gravity with which the driver presses on the cart does not do any work, since it is directed downward, perpendicular to the direction of movement.
The work of force is a scalar quantity.
Unit of work in the SI measurement system - joule. 1 joule is the work done by a force of 1 newton at a distance of 1 m if the directions of the force and displacement coincide.
If several forces act on a body or a material point, then we speak of the work done by their resultant force.
If the applied force is not constant, then its work is calculated as an integral:
Power
The force that sets a body in motion does mechanical work. But how this work is done, quickly or slowly, is sometimes very important to know in practice. After all, the same work can be completed in different times. The work that a large electric motor does can be done by a small motor. But he will need much more time for this.
In mechanics, there is a quantity that characterizes the speed of work. This quantity is called power.
Power is the ratio of work performed in a certain period of time to the value of this period.
N= A /∆ t
A-priory A = F s cos α , A s/∆ t = v , hence
N= F v cos α = F v ,
Where F - force, v speed, α – the angle between the direction of force and the direction of speed.
That is power – this is the scalar product of the force vector and the velocity vector of the body.
In the international SI system, power is measured in watts (W).
1 watt of power is 1 joule (J) of work done in 1 second (s).
Power can be increased by increasing the force doing work or the rate at which this work is done.