# Statics example from Meriam ( SI improper )

• lakuzamalakuzam
In summary, the conversation discusses the concept of partial constraints and how they can affect the tension in a system. It is mentioned that the top of a cosine function is horizontal and that this can lead to high tension forces in a diagonal link when the body is rotated. This phenomenon is compared to using a chain to retrieve a vehicle from a ditch, where the tension in the chain increases when pulled taut. Ultimately, the conversation highlights the practical applications of understanding partial constraints in various systems.
lakuzamalakuzam

could not understand why it is partial constraints. Also, I don't understand how link works. Below here is what I am thinking i think it is totally wrong can someone explain what's wrong with my idea here.

Welcome to PF.

The blue rectangle is not fully constrained by the three links within the frame. The position of A is fixed by the first two links, but the diagonal link 3 may be stretched as the body is rotated slightly about A.

The top of the cosine function at zero, is horizontal. Because the line from A to link 3 is straight, very high tension forces could be present in link 3 if the body was rotated slightly.

Lnewqban
As @Baluncore stated, the tension on link 3 goes to infinity when its attachment points are co-linear with point A. The situation is similar to a rope or chain stretched tight between two supports. Try calculating the tension when pushing on the center of the rope/chain span.

A practical use of the phenomena is retrieving a vehicle from a ditch.
Two people with a chain, a tree, and something to block the wheels, can pull the vehicle out. Providing there is a portion of the chain not being supported (by the ground):
1. chain taught between tree and vehicle
2. person 1 stands on the middle of the chain, deflecting it
3. person 2 chocks the vehicle wheels so can't roll back down into the ditch
4. person 1 steps off the chain and repeats from step (1)
Upon completion, they choose a different route.

Cheers,
Tom

berkeman

## 1. What is statics and why is it important in engineering?

Statics is a branch of mechanics that deals with the study of forces and their effects on rigid bodies at rest. It is important in engineering as it helps engineers design structures and machines that can withstand external forces and remain in equilibrium.

## 2. What is the SI improper system of units used in statics?

The SI improper system of units is a metric system of units used in statics, which includes the meter (m) for length, kilogram (kg) for mass, and second (s) for time. It also includes the newton (N) for force and pascal (Pa) for pressure.

## 3. How is the concept of moment applied in statics?

The concept of moment is applied in statics to analyze the rotational equilibrium of an object. It is the product of the force and the perpendicular distance from the force to the point of rotation. Moments can be either clockwise or counterclockwise, and their sum must be equal to zero for an object to be in rotational equilibrium.

## 4. What is the difference between a scalar and a vector in statics?

In statics, a scalar is a physical quantity that only has magnitude, such as mass or temperature. A vector, on the other hand, has both magnitude and direction, such as force or velocity. In order to fully describe a force in statics, both its magnitude and direction must be specified.

## 5. How do you calculate the center of mass in statics?

The center of mass in statics can be calculated by finding the weighted average of the position of all the particles in an object. This is done by multiplying the mass of each particle by its distance from a reference point, and then dividing the sum of these products by the total mass of the object. The resulting point is the center of mass.

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