G-force

G-forces are mentioned stresses acting on the human body, a commodity or a vehicle due to a strong change in the size and / or direction of speed. For loads of technical equipment such as aircraft or the indication of load limits, the term load factor is used. It is in the g- force is a " force per unit mass ," she therefore has the dimension of an acceleration and is a multiple of the acceleration due to gravity ( 9.8 m / s ² ) specified. High g - forces occur, for example when riding with a roller coaster, with missile launches or in collisions of objects.

• 3.1 Factors
• 3.2 directional dependence of symptoms
• 3.3 Historical Development

Physical Basics

A Formula 1 race car driver feels at startup to force him - contrary to the direction of acceleration - back pressed into its seat. This force arises from the fact that the race car is accelerating forward. The driver's body was because of its inertness to this acceleration remains when he was not carried away by the headquarters. What the driver feels so, is not an actual external force, the stronger pushes him back into the seat, but his own inertia that makes here in the form of an inertial force felt.

According to the basic equation of the mechanism of the driver ( mass ) body undergoes acceleration, when a force acts on it. It can also mean braking or changing the direction of physical term acceleration depending on the direction of the force colloquial. The driver is relative to its vehicle alone. In physics this is called an accelerated frame of reference. For him, there is a balance of power between the accelerating force and the inertial force. The inertia force is therefore equal and opposite as the external force. Therefore, the acceleration is to quantify the related to the inertia force. Here, then, the acceleration is often given as a multiple of the acceleration of gravity, because it is easy to compare with the everyday experience: " " So, it means that the experienced acceleration is equal to the acceleration due to gravity and that, consequently, the inertial force equal to the weight force (on the earth).

Special cases

Even straight-line acceleration

When a body is accelerated to the distance from the rest to the speed, then its acceleration is:

This follows by switching from the distance-time and velocity-time laws of uniformly accelerated motion:

The same formula is obtained for the amount of acceleration in a body that brakes on the track of the speed to zero ( See also Brake delay).

Cornering

If a body with the speed passes through a curve having the radius, it experiences the acceleration

Examples of g- values ​​in nature, technology and everyday life

Effects of G- forces on the human body

Factors

The effect of G- forces on the human body are strongly dependent on the direction of action. Usually, a coordinate system as in the image is used right. Positive g - forces in the z- direction experienced by an organism, for example, when it is pressed on a roller coaster in the seat with an inside loop; negative, if it is lifted at an outer loop from the seat.

In addition to the strength and direction of the forces is also of great importance, as long as they act. Briefly, the human body can withstand relatively high pressures ( where " short " periods of fractional seconds are meant ). For longer-lasting forces already exists from a comparatively small thickness the risk of circulatory disorders.

To be able to endure occurring in fighter aircraft g - load better, their crews anti-g suits are adjusted, which should limit the effects of g - forces.

Directional dependence of the symptoms

For positive g - forces in the z- direction ( exercised by the seat and floor, the seated man after accelerating above) there is a risk that the blood sags in the legs. This can lead to vision problems to unconsciousness due to reduced cerebral blood flow occur ( loss of consciousness). This phenomenon is also referred to as G- LOC ( "loss of consciousness" ). The unconsciousness precedes the so-called Greyout and later blackout coming through the insufficient blood supply to the retina (retina ) of the eye about. Once the acceleration forces no longer act, the brain and eyes blood flow is back to normal, and there is an awakening of the consciousness. The table below summarizes the responses of the untrained human body are listed on various ( lasting several minutes ) positive g - forces in the z- direction.

Negative g - forces in the z- direction ( harness pulls the man down) cause a flow of blood towards the head. They can be tolerated by people much worse. Just two to three grams can lead to Redout.

In x - direction (acceleration of the seated people at the front by pressure force of the arm of the chair ) g- forces of people will better endure, but lead from a strength of 20 g to breathing problems. In y - direction - cross-body - on the other hand is often when the head is not laterally supported, the overload of the muscles in the neck area the main problem.

Historical development

The effects of high g - values ​​were first extensively studied 1946-1948 by the American physician John Paul Stapp in the service of the U.S. Army. As part of the project while he himself and other volunteers were accelerated to rail- carriage by means of rocket propulsion to high speeds and slowed down with special braking devices. The results of this research contributed greatly to the development of effective retention and rescue systems.

G - forces in aviation

With g - forces that act on Aircraft in Flight, a distinction is made between maneuver loads and gust loads. Under gust loads is meant g - forces caused by gusts, ie by air movements that cause a momentary change in the approach flow, arise. Maneuvering loads resulting from flight maneuvers. To define stress limits of aircraft, the term " load factor " is used. The load factor is defined by the ratio of buoyancy force to gravitational force:

If it is assumed that no additional forces, such as by changing the engine power or speed change in the ambient air, result, corresponding to the load factor of the g - force acting on the people on board the aircraft. The load factor is the factor by which the apparent weight force increases to objects in the plane by additional inertial forces. Because of the slightly different dimension, however, is the load factor is a dimensionless number. In order to obtain the corresponding g - force, the load factor therefore usually has to be multiplied with the standard acceleration of gravity g. For a normal cruise flight, a load factor of results, corresponding to a g - force of 1 g

The designation of maximum load factor is used to determine the structural strength of an aircraft and thus allowable flight maneuvers.

Shock resistance

The resistance of a consumer item over a brief duration g forces from bumps and vibrations (vibrations ) is referred to as shock resistance. Information about shock resistance can be found, for example, often in data sheets of hard drives. The g - forces are usually very short endured ( order of 1 ms), often limit values ​​specified are only valid for a particular form of stress.