4º Post

Machines and mechanims

STABLE AND CENTRE OF GRAVITY

We say that a estructure is stable when it remains in equilibrium even when a force is applied to it.

 The centre of gravity is the point where the weight of an object is consdered to be concentrade.

We use the word machine to describe a set of elements or parts that work together and use energy to perform a task and use energy to perform a task and obtain a result.

Driver element: feeds energy to the machine (muscle strenght, in the case of scissors).

Driven element: receives the force produced in the machine (in the case of scissor, the sheet of paper or the piece of fabric).

Converting and/or transmitting element: transmits and/or converts (transforms) the motion (moviment) from the driver element to the driven element (in our example, two blades of the scissor).

MACHINE AND MECHANISMS

Devices that transmit and convert motion are called mechanisms.

*Explain the diference between motion transmission and motion conversion.

1.Motion transmission mechanisms. In this type, the mechanism is fed energy from the driver element and simply transfers it ot the driven element.

Examples: lever, pulleys, gears, worm gear...

2.Motion conversion mechanisms. In this type, the mechanism converts the movement from the driver element into a movement that the driven element can use.

Examples: cams, eccentric, srew and nut...

*What is a lever? Insert a picture.

A lever is a rigid bar that can pivot on a point of support called a fulcrum. It is used to lif load by applying force to a point on the bar. We call the aplied force effort, whereas the load to belifted or resistence that must be overcome is known as the resistance.

PULLEYS

Pulleys are used to lift heavy loads. They are wheels with a grooved rim.

Belt and pulley system:

This system is made up of two pulley wheels  joined by a belt that slot into the grooved rim of the wheels.  Examples: washing machines, cassette tapes...

Gear:

A gear is a mechanism consisting of two wheels with teeth.

Examples: a gear in a clock and gears in correction tape dispenser....

Tag machine:

2ºPost

  The basic stresses 

The basic stresses that a body may have to support are compression,tension,bending,torsion and shear.

 Compression:This is caused by forces acting on a body that tend to flatten it or reduce its length or thickness.

Tension:This is caused by forces acting on a body that tend to strech it.

Bending:This is caused by forces acting on an element that make it curve or bend.

Torsion:This caused by forces acting on a body that make it twist.

Shear: This is caused by two equal forces applied in opposite directions that act on lines of action close to each other.

What is rigidity?

If a material is rigid it does not change shape when force is applied to it.

Exercise 12: Think about the following objects and state whether they are rigid, plastic or elastic.

Ballon: Elastic  

Empty drinks can: Plastic

Window frame: Rigid 

Clay: Rigid 

Catapult: Rigid 

Door: Rigid

1.Structures :definition and types

STRUCTURES

A structure is a collection of elements arranged in an optimum way to support a body or an object. 

     Photo of a famous  structure in Spain:

    Types of stuctures:

Mass structures. These are solid, heavy and very sturdy strucutes. Examples include walls, dams,etc.

Frame structures. These structures are formen by columns and beams that act as supporting elements. One example might be the structure of a building.

Truss structures. These structure are composed of bars that form triangles. They are lightweight and sturdy. Examples  include cranes, electricity pylons, etc.

Suspended structure. These are held in place by cables and suspenders attached to sturdy supports. Examples include suspension bridges, tent, marquees, etc.

- A force is an influence that can deform a body or change its movement,or produce motion in a body rest.

-Stresses are the physical demands that a body or object must withstand when one or more external forces are applied to it 

Presentation

 Hi, we´re Ainhoa and Marian. We are going talking about structures and mechanisms.
:)