Elastic force body weight ground reaction force. Physics formulas

The force acting on the body from the support (or suspension) is called the support reaction force. When bodies come into contact, the support reaction force is directed perpendicular to the contact surface. If the body lies on a horizontal stationary table, the support reaction force is directed vertically upward and balances the force of gravity:

Wikimedia Foundation. 2010.

See what “Normal ground reaction force” is in other dictionaries:

Sliding friction force is the force that arises between contacting bodies during their relative motion. If there is no liquid or gaseous layer (lubricant) between the bodies, then such friction is called dry. Otherwise, friction... ... Wikipedia

The query "strength" redirects here; see also other meanings. Force Dimension LMT−2 SI units ... Wikipedia

The query "strength" redirects here; see also other meanings. Force Dimension LMT−2 SI units newton ... Wikipedia

Amonton Coulomb's law is an empirical law that establishes a connection between the surface friction force that occurs during relative sliding of a body with the normal reaction force acting on the body from the surface. Friction force, ... ... Wikipedia

Sliding friction forces are forces that arise between contacting bodies during their relative motion. If there is no liquid or gaseous layer (lubricant) between the bodies, then such friction is called dry. Otherwise, friction... ... Wikipedia

Static friction, adhesion friction is the force that arises between two contacting bodies and prevents the occurrence of relative motion. This force must be overcome in order to set two contacting bodies in motion each other... ... Wikipedia

The request “Upright walking” is redirected here. A separate article is needed on this topic. Human walking is the most natural human locomotion. An automated motor act carried out as a result of complex coordinated activity... ... Wikipedia

Walking cycle: support on one leg, double-support period, support on the other leg... Human walking is the most natural human locomotion. An automated motor act that occurs as a result of complex coordinated activity of skeletal ... Wikipedia

The friction force when a body slides on a surface does not depend on the area of contact of the body with the surface, but depends on the strength of the normal reaction of this body and on the state of the environment. The sliding friction force occurs when a given sliding... ... Wikipedia

Amonton Coulomb's law The force of friction when a body slides on a surface does not depend on the area of contact of the body with the surface, but depends on the force of the normal reaction of this body and on the state of the environment. The sliding friction force occurs when... ... Wikipedia

Reaction force supports refers to elastic forces, and is always directed perpendicular to the surface. It resists any force that causes the body to move perpendicular to the support. In order to calculate it, you need to identify and find out the numerical value of all the forces that act on the body standing on the support.

You will need

- scales;
- speedometer or radar;
- goniometer.

Instructions

Determine body weight using scales or any other method. If the body is on a horizontal surface (and it does not matter whether it is moving or at rest), then the support reaction force is equal to the force of gravity acting on the body. In order to calculate it, multiply the body mass by the acceleration of gravity, which is equal to 9.81 m/s² N=m g.
When a body moves along an inclined plane directed at an angle to the horizontal, the ground reaction force is at an angle to the force of gravity. At the same time, it compensates only for that component of gravity that acts perpendicular to the inclined plane. To calculate the reaction force of the support, use a protractor to measure the angle at which the plane is located to the horizontal. Calculate force support reactions, multiplying the body mass by the acceleration of gravity and the cosine of the angle at which the plane is located to the horizon N=m g Cos(α).
If a body moves along a surface that is a part of a circle with a radius R, for example, a bridge, a hillock, then the support reaction force takes into account the force acting in the direction from the center of the circle, with an acceleration equal to the centripetal one, acting on the body. To calculate the reaction force of the support at the top point, subtract the ratio of the square of the velocity to the radius of curvature of the trajectory from the acceleration of gravity.
Multiply the resulting number by the mass of the moving body N=m (g-v²/R). Speed should be measured in meters per second and radius in meters. At a certain speed, the value of the acceleration directed from the center of the circle can equal or even exceed the acceleration of gravity, at which point the adhesion of the body to the surface will disappear, therefore, for example, motorists need to clearly control the speed on such sections of the road.
If the curvature is directed downward and the body’s trajectory is concave, then calculate the support reaction force by adding to the free fall acceleration the ratio of the square of the velocity and the radius of curvature of the trajectory, and multiply the resulting result by the mass of the body N=m (g+v²/R).
If the friction force and friction coefficient are known, calculate the support reaction force by dividing the friction force by this coefficient N=Ftr/μ.

Testing online

What you need to know about strength

Force is a vector quantity. It is necessary to know the point of application and direction of each force. It is important to be able to determine which forces act on the body and in what direction. Force is denoted as , measured in Newtons. In order to distinguish between forces, they are designated as follows

Below are the main forces operating in nature. It is impossible to invent forces that do not exist when solving problems!

There are many forces in nature. Here we consider the forces that are considered in the school physics course when studying dynamics. Other forces are also mentioned, which will be discussed in other sections.

Gravity

Every body on the planet is affected by the Earth's gravity. The force with which the Earth attracts each body is determined by the formula

The point of application is at the center of gravity of the body. Gravity always directed vertically downwards.

Friction force

Let's get acquainted with the force of friction. This force occurs when bodies move and two surfaces come into contact. The force occurs because surfaces, when viewed under a microscope, are not as smooth as they appear. The friction force is determined by the formula:

The force is applied at the point of contact of two surfaces. Directed in the direction opposite to movement.

Ground reaction force

Let's imagine a very heavy object lying on a table. The table bends under the weight of the object. But according to Newton's third law, the table acts on the object with exactly the same force as the object on the table. The force is directed opposite to the force with which the object presses on the table. That is, up. This force is called the ground reaction. The name of the force "speaks" support reacts. This force occurs whenever there is an impact on the support. The nature of its occurrence at the molecular level. The object seemed to deform the usual position and connections of the molecules (inside the table), they, in turn, strive to return to their original state, “resist.”

Absolutely any body, even a very light one (for example, a pencil lying on a table), deforms the support at the micro level. Therefore, a ground reaction occurs.

There is no special formula for finding this force. It is denoted by the letter , but this force is simply a separate type of elasticity force, so it can also be denoted as

The force is applied at the point of contact of the object with the support. Directed perpendicular to the support.

Since the body is represented as a material point, force can be represented from the center

Elastic force

This force arises as a result of deformation (change in the initial state of the substance). For example, when we stretch a spring, we increase the distance between the molecules of the spring material. When we compress a spring, we decrease it. When we twist or shift. In all these examples, a force arises that prevents deformation - the elastic force.

The elastic force is directed opposite to the deformation.

When connecting springs in series, for example, the stiffness is calculated using the formula

When connected in parallel, the stiffness

Sample stiffness. Young's modulus.

Young's modulus characterizes the elastic properties of a substance. This is a constant value that depends only on the material and its physical state. Characterizes the ability of a material to resist tensile or compressive deformation. The value of Young's modulus is tabular.

Read more about the properties of solids here.

Body weight is the force with which an object acts on a support. You say, this is the force of gravity! The confusion occurs in the following: indeed, often the weight of a body is equal to the force of gravity, but these forces are completely different. Gravity is a force that arises as a result of interaction with the Earth. Weight is the result of interaction with the support. The force of gravity is applied at the center of gravity of the object, while weight is the force that is applied to the support (not to the object)!

There is no formula for determining weight. This force is designated by the letter.

The support reaction force or elastic force arises in response to the impact of an object on the suspension or support, therefore the weight of the body is always numerically the same as the elastic force, but has the opposite direction.

The support reaction force and weight are forces of the same nature; according to Newton’s 3rd law, they are equal and opposite in direction. Weight is a force that acts on the support, not on the body. The force of gravity acts on the body.

Body weight may not be equal to gravity. It may be more or less, or it may be that the weight is zero. This condition is called weightlessness. Weightlessness is a state when an object does not interact with a support, for example, the state of flight: there is gravity, but the weight is zero!

It is possible to determine the direction of acceleration if you determine where the resultant force is directed

Please note that weight is force, measured in Newtons. How to correctly answer the question: “How much do you weigh”? We answer 50 kg, not naming our weight, but our mass! In this example, our weight is equal to gravity, that is, approximately 500N!

Overload- ratio of weight to gravity

Archimedes' force

Force arises as a result of the interaction of a body with a liquid (gas), when it is immersed in a liquid (or gas). This force pushes the body out of the water (gas). Therefore, it is directed vertically upward (pushes). Determined by the formula:

In the air we neglect the power of Archimedes.

If the Archimedes force is equal to the force of gravity, the body floats. If the Archimedes force is greater, then it rises to the surface of the liquid, if less, it sinks.

Electrical forces

There are forces of electrical origin. Occurs in the presence of an electrical charge. These forces, such as the Coulomb force, Ampere force, Lorentz force, are discussed in detail in the Electricity section.

Schematic designation of forces acting on a body

Often the body is modeled as a material point. Therefore, in diagrams, various points of application are transferred to one point - to the center, and the body is depicted schematically as a circle or rectangle.

In order to correctly designate forces, it is necessary to list all the bodies with which the body under study interacts. Determine what happens as a result of interaction with each: friction, deformation, attraction, or maybe repulsion. Determine the type of force and correctly indicate the direction. Attention! The amount of forces will coincide with the number of bodies with which the interaction occurs.

The main thing to remember

1) Forces and their nature;
2) Direction of forces;
3) Be able to identify the acting forces

Friction forces*

There are external (dry) and internal (viscous) friction. External friction occurs between contacting solid surfaces, internal friction occurs between layers of liquid or gas during their relative motion. There are three types of external friction: static friction, sliding friction and rolling friction.

Rolling friction is determined by the formula

The resistance force occurs when a body moves in a liquid or gas. The magnitude of the resistance force depends on the size and shape of the body, the speed of its movement and the properties of the liquid or gas. At low speeds of movement, the drag force is proportional to the speed of the body

At high speeds it is proportional to the square of the speed

The relationship between gravity, the law of gravity and the acceleration of gravity*

Let's consider the mutual attraction of an object and the Earth. Between them, according to the law of gravity, a force arises

Now let's compare the law of gravity and the force of gravity

The magnitude of the acceleration due to gravity depends on the mass of the Earth and its radius! Thus, it is possible to calculate at what acceleration objects will fall on the Moon or on any other planet, using the mass and radius of that planet.

The distance from the center of the Earth to the poles is less than to the equator. Therefore, the acceleration of gravity at the equator is slightly less than at the poles. At the same time, it should be noted that the main reason for the dependence of the acceleration of gravity on the latitude of the area is the fact of the Earth’s rotation around its axis.

As we move away from the Earth's surface, the force of gravity and the acceleration of gravity change in inverse proportion to the square of the distance to the center of the Earth.

Ground reaction force. Weight

Let's place the stone on the horizontal lid of a table standing on the Earth (Fig. 104). Since the acceleration of the stone relative to the Earth is equal to a bullet, then according to Newton’s second law, the sum of the forces acting on it is zero. Consequently, the effect of gravity m · g on the stone must be compensated by some other forces. It is clear that under the influence of the stone the table top is deformed. Therefore, an elastic force acts on the stone from the side of the table. If we assume that the stone interacts only with the Earth and the table top, then the elastic force should balance the force of gravity: F control = -m · g. This elastic force is called ground reaction force and are denoted by the Latin letter N. Since the acceleration of gravity is directed vertically downwards, the force N is directed vertically upwards - perpendicular to the surface of the table top.

Since the table top acts on the stone, then, according to Newton’s third law, the stone also acts on the table top with a force P = -N (Fig. 105). This force is called weight.

The weight of a body is the force with which this body acts on a suspension or support while being stationary relative to the suspension or support.

It is clear that in the case considered, the weight of the stone is equal to the force of gravity: P = m · g. This will be true for any body resting on a suspension (support) relative to the Earth (Fig. 106). Obviously, in this case, the suspension attachment point (or support) is motionless relative to the Earth.

For a body resting on a suspension (support) that is motionless relative to the Earth, the weight of the body is equal to the force of gravity.

The weight of the body will also be equal to the force of gravity acting on the body if the body and the suspension (support) move uniformly in a straight line relative to the Earth.

If the body and the suspension (support) move relative to the Earth with acceleration so that the body remains motionless relative to the suspension (support), then the weight of the body will not be equal to the force of gravity.

Let's look at an example. Let a body of mass m lie on the floor of the elevator, the acceleration a of which is directed vertically upward (Fig. 107). We will assume that only the force of gravity m g and the floor reaction force N act on the body. (The weight of the body acts not on the body, but on the support - the floor of the elevator.) In a reference frame stationary relative to the Earth, the body on the floor of the elevator moves with elevator with acceleration a. According to Newton's second law, the product of body mass and acceleration is equal to the sum of all forces acting on the body. Therefore: m · a = N – m · g.

Therefore, N = m · a + m · g = m · (g + a). This means that if the elevator has an acceleration directed vertically upward, then the modulus of the floor reaction force N will be greater than the modulus of gravity. In fact, the floor reaction force must not only compensate for the effect of gravity, but also give the body acceleration in the positive direction of the X axis.

Force N is the force with which the elevator floor acts on the body. According to Newton's third law, a body acts on the floor with a force P, the modulus of which is equal to the modulus N, but the force P is directed in the opposite direction. This force is the weight of the body in the moving elevator. The modulus of this force is P = N = m (g + a). Thus, in an elevator moving with acceleration directed upward relative to the Earth, the modulus of body weight is greater than the modulus of gravity.

This phenomenon is called overload.

For example, let the acceleration a of the elevator be directed vertically upward and its value equal to g, i.e. a = g. In this case, the modulus of the body's weight - the force acting on the floor of the elevator - will be equal to P = m (g + a) = m (g + g) = 2m g. That is, the weight of the body will be twice as much as in an elevator, which is at rest relative to the Earth or moves uniformly in a straight line.

For a body on a suspension (or support) moving with acceleration relative to the Earth directed vertically upward, the weight of the body is greater than the force of gravity.

The ratio of the weight of a body in an elevator moving with acceleration relative to the Earth to the weight of the same body in an elevator at rest or moving uniformly in a straight line is called load factor or, more briefly, overload.

Overload coefficient (overload) - the ratio of body weight during overload to the force of gravity acting on the body.

In the case considered above, the overload is equal to 2. It is clear that if the acceleration of the elevator was directed upward and its value was equal to a = 2g, then the overload factor would be equal to 3.

Now imagine that a body of mass m lies on the floor of an elevator, the acceleration of which a relative to the Earth is directed vertically downward (opposite to the X axis). If the elevator acceleration modulus a is less than the gravitational acceleration modulus, then the elevator floor reaction force will still be directed upward, in the positive direction of the X axis, and its modulus will be equal to N = m (g - a). Consequently, the modulus of the body’s weight will be equal to P = N = m (g - a), i.e., it will be less than the modulus of gravity. Thus, the body will press on the floor of the elevator with a force whose modulus is less than the modulus of gravity.

This feeling is familiar to anyone who has ridden a high-speed elevator or swung on a large swing. As you move down from the top, you feel your pressure on the support decrease. If the acceleration of the support is positive (the elevator and the swing begin to rise), you are pressed harder against the support.

If the acceleration of the elevator relative to the Earth is directed downward and is equal in magnitude to the acceleration of gravity (the elevator falls freely), then the floor reaction force will become equal to zero: N = m (g - a) = m (g - g) = 0. B In this case, the elevator floor will stop putting pressure on the body lying on it. Consequently, according to Newton’s third law, the body will not put pressure on the floor of the elevator, making a free fall together with the elevator. Body weight will become zero. This condition is called state of weightlessness.

The state in which the body's weight is zero is called weightlessness.

Finally, if the acceleration of the elevator towards the Earth becomes greater than the acceleration of gravity, the body will be pressed against the ceiling of the elevator. In this case, the body weight will change its direction. The state of weightlessness will disappear. This can be easily verified if you sharply pull down the jar with the object in it, covering the top of the jar with your palm, as shown in Fig. 108.

Results

The weight of a body is the force with which this body acts on a tray or support while being stationary relative to the suspension or support.

The weight of a body in an elevator moving with acceleration directed upward relative to the Earth has a modulus greater than the modulus of gravity. This phenomenon is called overload.

Overload coefficient (overload) - the ratio of the body weight during overload to the force of gravity acting on this body.

If the body weight is zero, then this state is called weightlessness.

Questions

What force is called the ground reaction force? What is body weight called?
What is the weight of the body applied to?
Give examples when body weight: a) is equal to gravity; b) equal to zero; c) more gravity; d) less gravity.
What is called overload?
What state is called weightlessness?

Exercises

Seventh-grader Sergei stands on bathroom scales in his room. The instrument needle is positioned opposite the 50 kg mark. Determine the modulus of Sergei's weight. Answer the other three questions about this power.
Find the overload experienced by an astronaut who is in a rocket rising vertically with acceleration a = 3g.
What force does an astronaut with mass m = 100 kg exert on the rocket indicated in Exercise 2? What is this force called?
Find the weight of an astronaut with mass m = 100 kg in a rocket that: a) stands motionless on the launcher; b) rises with acceleration a = 4g, directed vertically upward.
Determine the magnitude of the forces acting on a weight of mass m = 2 kg, which hangs motionless on a light thread attached to the ceiling of the room. What are the moduli of the elastic force acting on the side of the thread: a) on the weight; b) on the ceiling? What is the weight of the weight? Directions: Use Newton's laws to answer the questions.
Find the weight of a load of mass m = 5 kg suspended on a thread from the ceiling of a high-speed elevator if: a) the elevator rises uniformly; b) the elevator descends evenly; c) the elevator rising upward at a speed v = 2 m/s began braking with an acceleration a = 2 m/s 2 ; d) the elevator going down at a speed v = 2 m/s began braking with an acceleration a = 2 m/s 2 ; e) the elevator began to move upward with acceleration a = 2 m/s 2 ; e) the elevator began to move downward with an acceleration a = 2 m/s 2 .

NEWTON'S LAWS TYPES OF FORCES. Types of forces Elastic force Friction force Gravity force Archimedes force Tension force of a thread Support reaction force Body weight Universal force. - presentation

Presentation on the topic: "NEWTON'S LAWS TYPES OF FORCES. Types of forces Elastic force Friction force Gravity force Archimedes force Tension force of a thread Support reaction force Body weight Universal force.” - Transcript:

1 NEWTON'S LAWS TYPES OF FORCES

2 Types of forces Elastic force Friction force Gravity force Archimedes force Force of thread tension Support reaction force Body weight Force of universal gravitation

3 Newton's laws. 1 LawLaw2 LawLaw3 Law

4 1 Newton's law. There are reference systems called inertial, relative to which free bodies move uniformly and rectilinearly. Laws

5 2 Newton's law. The product of a body's mass and its acceleration is equal to the sum of the forces acting on the body. Laws

6 3 Newton's law. The forces with which bodies act on each other are equal in magnitude and directed in one straight line in opposite directions. Laws

7 SSSS IIII LLLL AAAAA V in the SSSS Oil MMMM IIII Rrrr NNNN LLC GGG LLC TTTT YAYAYA YAYAYA TTTT EDUE NNNNNNEII YAYAIAYA. G – gravitational constant. m – body mass r – distance between the centers of bodies.

8 SSSS iiiii lllll aaaa in v in ssss eee mmmm iii rrrr nnnn ooooo yyyy ooooo t t t t yayyy yyyy oooo tttt eee nnnn iii yay - – - – pppp rrrr eeee tttt yayay zhzhzh eee nnnn eeee eee t t t t eee lllll d d d d rrrrr uuu yyyy k k k k d d d d rrrrr uuuu yyyy uuuu. NNNNN aaaa pppp rrrrr aaaa vvvv lllll eee nnnn aaaa p p p p ooooo p p p p prrrr yay mmmm oooo yyyy. SSSS OOOOEEED DDDD III NNNNNNEY Yuyuyuye EDUSHSHSHSHEYE YIYY TCTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTSYYYY TO T T T TOEEELLL.

9 ССССaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaall

10 N NN Ground reaction force – (N) – the action of support on the body, directed perpendicular to the support. Ground reaction force

11 Frictional force Frictional force This is the action of a surface on a moving or trying to move body, directed against the movement or possible movement. If the body does not move, then the frictional force is equal to the applied force. If the body is moving or just starting to move, then the friction force is found according to the formula: - friction coefficient N - support reaction force Friction force

12 Elastic force Elastic force Elastic force is the action of an elastically deformed body. Directed against deformation.

13 Action of a body on a support or suspension WEIGHT |P|=|N| |P|=|T|

14 Archimedes' force The Archimedes' force is the force with which a liquid acts on a body immersed in it. THE POWER OF ARCHIMEDES

15 GRAVITY Force Gravity is the force with which the earth acts on a body, directed towards the center of the earth.

Support reaction force law

Rice. 7. Tensile forces

If the ground reaction becomes zero, the body is said to be in a state weightlessness. In a state of weightlessness, the body moves only under the influence of gravity.

1.2.3. Inertia and inertia. Inertial reference systems.

Newton's first law

Experience shows that any body resists attempts to change its state, regardless of whether it is moving or at rest. This property of bodies is called inertia. The concept of inertia should not be confused with the inertia of bodies. Inertia bodies is manifested in the fact that in the absence of external influences, bodies are in a state of rest or rectilinear and uniform motion until some external influence changes this state. Inertia, unlike inertia, does not have a quantitative characteristic.

Dynamics problems are solved using three basic laws, called Newton's laws. Newton's laws are satisfied in inertial reference systems. Inertial reference systems (ISO)- these are reference systems in which bodies, not affected by other bodies, move without acceleration, that is, rectilinearly and uniformly, or are at rest.

Newton's first law (law of inertia): There are such reference systems (so-called inertial systems), for which any material point, in the absence of external influences, moves uniformly and rectilinearly or is at rest. According to Galileo's principle of relativity all mechanical phenomena in different inertial reference systems proceed in the same way and no mechanical experiments can establish whether a given reference system is at rest or moves rectilinearly and uniformly.

1.2.4. Newton's second law. Body impulse and force impulse.

Law of conservation of momentum. Newton's third law

Newton's second law: acceleration acquired by a material point under the action of one or more forces is directly proportional to the acting force (or the resultant of all forces), inversely proportional to the mass of the material point and the direction coincides with the direction of the acting force (or resultant):

. (8)

Newton's second law has another form of notation. Let us introduce the concept of body momentum.

Body impulse(or simply, impulse) - a measure of mechanical movement determined by the product of body mass
at his speed , i.e.,
. Let's write down Newton's second law - the basic equation for the dynamics of translational motion:

Let us replace the sum of forces with its resultant
and the entry for Newton’s second law takes the following form:

, (9)

and Newton’s second law itself can also be formulated as follows: the rate of change of momentum determines the force acting on the body.

Let's transform the last formula:
. Magnitude
got the name impulse of force. Impulse force
determined by the change in body momentum
.

A mechanical system of bodies that is not acted upon by external forces is called closed(or isolated).

Law of conservation of momentum: the momentum of a closed system of bodies is a constant quantity.

Newton's third law: the forces arising during the interaction of bodies are equal in magnitude, opposite in direction and applied to different bodies (Fig. 8):

. (10)

Rice. 8. Newton's third law

From Newton's 3rd law it follows that When bodies interact, forces arise in pairs. In addition to Newton’s laws, the complete system of laws of dynamics must include principle of independent action of forces: the action of any force does not depend on the presence or absence of other forces; the combined action of several forces is equal to the sum of the independent actions of the individual forces.

Normal ground reaction force

Wikimedia Foundation. 2010.

See what “Normal ground reaction force” is in other dictionaries:

Sliding friction force- The force of sliding friction is the force that arises between contacting bodies during their relative motion. If there is no liquid or gaseous layer (lubricant) between the bodies, then such friction is called dry. Otherwise, friction... ... Wikipedia

Strength (physical quantity)- The request for "power" is redirected here; see also other meanings. Force Dimension LMT−2 SI units ... Wikipedia

Force- The request for "power" is redirected here; see also other meanings. Force Dimension LMT−2 SI units newton ... Wikipedia

Amonton's Law- Amonton Coulomb's law is an empirical law that establishes a connection between the surface friction force that occurs during relative sliding of a body with the normal reaction force acting on the body from the surface. Friction force, ... ... Wikipedia

Law of Friction- Sliding friction forces are forces that arise between contacting bodies during their relative motion. If there is no liquid or gaseous layer (lubricant) between the bodies, then such friction is called dry. Otherwise, friction... ... Wikipedia

Static friction- Static friction, adhesion friction is the force that arises between two contacting bodies and prevents the occurrence of relative motion. This force must be overcome in order to set two contacting bodies in motion each other... ... Wikipedia

walking man- The request “Upright walking” is redirected here. A separate article is needed on this topic. Human walking is the most natural human locomotion. An automated motor act carried out as a result of complex coordinated activity... ... Wikipedia

Upright walking- Walking cycle: support on one leg, double support period, support on the other leg. Human walking is the most natural human locomotion. An automated motor act that occurs as a result of complex coordinated activity of skeletal ... Wikipedia

Amonton-Coulomb law- the friction force when a body slides on a surface does not depend on the area of contact of the body with the surface, but depends on the force of the normal reaction of this body and on the state of the environment. The sliding friction force occurs when a given sliding... ... Wikipedia

Coulomb's law (mechanics)- Amonton Coulomb's law, the force of friction when a body slides on a surface does not depend on the area of contact of the body with the surface, but depends on the force of the normal reaction of this body and on the state of the environment. The sliding friction force occurs when... ... Wikipedia

Normal reaction strength- the force acting on the body from the side of the support (or suspension). When bodies come into contact, the reaction force vector is directed perpendicular to the contact surface. The following formula is used for calculation:

$|\vec N|= mg \cos \theta,$

Where $|\vec N|$ - modulus of the normal reaction force vector, $m$ - body mass, $g$ - acceleration of gravity , $\theta$ - the angle between the support plane and the horizontal plane.

According to Newton's third law, the modulus of the normal reaction force $|\vec N|$ equal to body weight modulus $|\vec P|$ , but their vectors are collinear and oppositely directed:

$\vec N= -\vec P.$

From the Amonton-Coulomb law it follows that for the modulus of the normal reaction force vector the following relation is true:

$|\vec N|= \frac(|\vec F|)(k),$

Where $\vec F$ - sliding friction force, and $k$ - friction coefficient.

Since the static friction force is calculated by the formula

$|\vec f|= mg \sin \theta,$

then we can experimentally find such an angle value $\theta$ , at which the static friction force will be equal to the sliding friction force:

$mg \sin \theta = k mg \cos \theta.$

From here we express the friction coefficient:

$k = \mathrm(tg)\ \theta.$

Write a review of the article "The Power of Normal Reaction"

An excerpt characterizing the strength of a normal reaction

All historians agree that the external activities of states and peoples, in their clashes with each other, are expressed by wars; that directly, as a result of greater or lesser military successes, the political power of states and peoples increases or decreases.
No matter how strange the historical descriptions are of how some king or emperor, having quarreled with another emperor or king, gathered an army, fought with the enemy army, won a victory, killed three, five, ten thousand people and, as a result, conquered the state and an entire people of several millions; no matter how incomprehensible it may be why the defeat of one army, one hundredth of all the forces of the people, forced the people to submit, all the facts of history (as far as we know it) confirm the justice of the fact that greater or lesser successes of the army of one people against the army of another people are the reasons or, according to at least significant signs of an increase or decrease in the strength of nations. The army was victorious, and the rights of the victorious people immediately increased to the detriment of the vanquished. The army suffered defeat, and immediately, according to the degree of defeat, the people are deprived of their rights, and when their army is completely defeated, they are completely subjugated.
This has been the case (according to history) from ancient times to the present day. All Napoleon's wars serve as confirmation of this rule. According to the degree of defeat of the Austrian troops, Austria is deprived of its rights, and the rights and strength of France increase. The French victory at Jena and Auerstätt destroys the independent existence of Prussia.

Methods determination of support reactions are studied in the course of theoretical mechanics. Let us dwell only on the practical issues of the method of calculating support reactions, in particular for a simply supported beam with a cantilever (Fig. 7.4).

We need to find the reactions: , and . The directions of reactions are chosen arbitrarily. Let's direct both vertical reactions upward, and the horizontal reaction to the left.

Finding and checking support reactions in a hinged support

To calculate the values of the support reactions, we compile static equations:

The sum of the projections of all forces (active and reactive) onto the axisz is zero: .

Since only vertical loads (perpendicular to the axis of the beam) act on the beam, then from this equation we find: horizontal motionless reaction.

The sum of the moments of all forces relative to support A is equal to zero:.

For the moment of force: we consider the moment of force to be positive if it rotates the beam relative to a point counterclockwise.

It is necessary to find the distributed resultant. The distributed linear load is equal to the area of the distributed load and is applied in this diagram (in the middle of a section of length ).

The sum of the moments of all forces relative to support B is equal to zero:.

The minus sign as a result says: the preliminary direction of the ground reaction was chosen incorrectly. We change the direction of this support reaction to the opposite (see Fig. 7.4) and forget about the minus sign.

Checking support reactions

The sum of the projections of all forces onto the axisymust be equal to zero: .

Forces whose direction coincides with the positive direction of the y-axis are projected onto it with a plus sign.