4th Post: Machines and mechanisms

·We say that a structure is stable when it remins in equilibrium even when a force is applied to it.

·Centre of gravity: It is the point where the weight of an object is considered to be concetrated.

·Machine: Is used to describe a set of elements or parts that work together and use energy to perform a task and obtain a result.

There are three components all machine has:

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

Driven element: Recived the force produced in the machine (in the case of scissors, the sheet of papper or the piece of fabric).

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

Mechanisms: Are devices that transmit and/or convert motion

Difference between motion transmission and motion conversion:

In motion transmition, the mechanism is fed energy from the driver element and simply tranfers it to the driven element.
In the motion converts, the mechanism converts the movement form the driver element into a movement that the driven element can use.

Lever: Is a rigid barthat can pivot on a point of support called a Fulcrum. It is used to lift load by applying force to a point on the bar.

Pulley: Are wheels with a grooved rim that are used to lift heavy loads.

Belt and puley systems: The system is made up of two pulley wheels joined by a belt that slots into the grooved rim of the wheels. Example: A motor

Gear: Is a mechanism consisting in two wheels with teeth. Example:

3 post:Stresses and rigidity

·Stresses: Are the physical demands that a body or object must withstand when one or more external force are appplied to it.

· Types of stresses:

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

·Tension(or Traction): This is caused by foces acting on a body that tend to stretch it.

·Bending: This is caused by forces acting on an element that make it curved or bend. It is done by supporting the two ends and applying force in the centre.

·Torsion: This is 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. Shear stress will tend to cut the material if it cannot twist or bend

·Ridigity: If a material is rigid, does not change shape when force is applied to it. By contrast, if the material does change shape, we say that it is deformable.

12. think about the following object and start whether they are rigid, plastic or elastic: ballon, empty drinks can, window frame, clay, catapult, door.
Rigid: Door, catapult.
Plastic: Window frame, empy drinks can.
Elastic: Clay, ballon.

2nd Post

·Definition of structure: A structure is a collection of elements arranged in an optimun way to support a body or an object.

·There are four types of structures:

·Mass structures: This ones are solid,heavy and very sturdy structures. Like walls, dams, etc.

·Frame structures: These structures are formed by columns and beams that act as supporting elements. An example is a structure of a building.

·Truss structures: These structures are composed of bars that form triangles. They are ligthweigth and sturdy

·Suspended structures: These are held in place by cables and suspenders attached to sturdy supports. Examples: Include suspension bridges, tents, marquees, etc.

 

Mass structure                                                          Frame structure  

Truss structures                                                           Suspended structures


·Force: A force is an influence that can deform a body or change it movement, or produce motion in a body at rest.

·Stresses: Are the physical demands that a body or object must withstand when one or more external force are appplied to it

    

Presentation

Hello our names are Miguel and Alexander and we are going to talk about structures