Mechanical work

Mechanical work is performed when a body is moved or deformed by a force.

Formula sign: W
units: one Newton meter ( 1 Nm)
one joule (1 J)

Mechanical work describes a procedure or process. It is therefore also called a process variable.

Work in mechanics

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Conversion of mechanical energy

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Mechanical work

Mechanical work

In everyday life, activities in which we have to exert ourselves are called work. Such activities are z. B. Carrying a suitcase, riding a bicycle, stretching an expander, or learning a poem. In some of these activities, we apply a force to move or deform a body.
In all physical processes in which a body is moved or deformed by a force, one performs mechanical work.

Definition of mechanical work

Mechanical work is done when a body is moved or deformed by a force.

Formula sign: W
Units: one Newton meter ( 1 Nm)
one joule (1 J)

Work of 1 Nm is done when a force of 1 N acts on a body, causing the body to move 1 m in the direction of the acting force. the unit one newton meter is also called one joule (pronounced dschul) in honor of the English physicist JAMES PRESCOTT JOULE (1818-1889). It is valid

Multiples of the unit 1 J are one kilojoule (1 kJ) and one megajoule (MJ):

1 kJ = 1 000 J
1 MJ = 1 000 kJ = 1 000 000 J

In the following overview typical values for mechanical work are given.

Mechanical work describes a procedure or process. It is therefore also referred to as a process variable.

Mechanical work done in moving or lifting a body

Types of mechanical work

Depending on the way in which mechanical work is performed, one distinguishes between various special types of mechanical work .
If a body is lifted by a force, lifting work is performed. As a rule, a constant force acts in the direction of the movement.
If the motion of a body is inhibited by a frictional force, this is called friction work .
If a body is accelerated by a force, acceleration work is done on it.
If a body is deformed by a force, one speaks of deformation work , in the case of the deformation of a spring also of spring tension work .
If the volume of an enclosed gas is reduced by a force, volume change work, or Volume work performed.
Notes on the individual types of mechanical work are given under the relevant keywords.

Calculation of mechanical work

Under certain conditions, the mechanical work can be calculated or derived from a force-distance diagram (F-s-diagram) can be determined.
Under the condition that the force is constant and acts in the direction of the path:

W = F ⋅ s F acting force s distance traveled

The concept of work as the product of force and displacement was developed by the French mathematician J. V. PONCELET (1788-1867) with the support of the French engineer and physicist G. G. CORIOLIS (1792-1843) introduced into physics around 1826.

Force and displacement have the same direction

In Force-displacement diagram the area under the graph is equal to the mechanical work done. Consequently, the mechanical work can also be determined by counting the surface area. The units in which the quantities are plotted must be taken into account here.

Force-displacement diagram: the area under the graph is equal to the mechanical work done.

If the force does not act in the direction of the path, then only the component of the force that acts in the direction of the path plays a role for the mechanical work (Fig. 5). It is true in this case:

W = F s ⋅ s W = F ⋅ s ⋅ cos α

If a force acts perpendicular to the distance traveled, the mechanical work done is zero. This is z. B. the case when a load is suspended from a crane hook at a certain height and the crane rotates. The mechanical work is also zero, if a force acts, but no distance is covered. That is z. B. the case when you have a bag in your hand but are standing still.

Force and distance have different directions. Decisive for the work is only the conpoments of the force in the direction of travel.

BWS-PHY-0305-13.mcd

When a spring is stretched, the force acts in the direction of travel but is not constant. In such cases the mechanical work can be calculated from F-s-diagram can be determined by counting the area or by calculating the area (Fig. 6). The counting of the area can be done even if the force changes unevenly along the path.

Relationship between work and energy

If mechanical work is performed on a body or by a body, its energy changes . Thus, z increases. B. when lifting a body its potential energy. When a car accelerates, its kinetic energy increases. When performing frictional work while braking a bicycle, its kinetic energy decreases. In general:

The mechanical work done by or on a body is equal to the change in its energy.

The energy of the body can increase or decrease in the process. It depends on the particular conditions.

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