4th post- Machines & Mechanisms

Machines & Mechanisms

 1-When a structure is stable ?

 We say that a structure is stable when it remainds in equilibrium even when a force is applied to it  

 2-When is the centre of gravity ?

  The centre of gravity is the point where the weight of an object is considered to be concentrated.

3-What is a machine ?

 We use the word machine to describe a set of elements or parts thet work together and use energy to perform a task and obtain a result.It has three components:

1-Driver element: feeds energy to the machine 

2-Driven element : recieves the force produced in the machine

3-Converting and/or trasmitting element-: trasmits and / or converts the motion from the driver element to the driven element,

4-What is mechanism ?

 Devices that transmit an/or convert motion.

Motion transmission mechanisms:the mechanism is feed enrgy from the driver element and simply transfers it to the driven elements.

We can class motion transmissions machines as:

• Linear transmission mechanisms. there are type ofsimple machine.
• Rotary transmission mechanisms. these include friction wheels ,belt and pulley systems ,gears, chain and sprocket systems,and woems gears.

  Motion conversion mechanisms. The mechanism converts the mpvement from the driver element into a movement that the driven element can use.Example:nuts and bolts.                                           

5-What is a lever ?

A lever is a rigid bar that can pivot on point of support called a fulcrum.

5-What is a pulley?

Is used to lift heavy loads.they are wheels with a grooved rim

6-Belt and pulley system

This system is made up of 2 pulley wheels joined by a belt that slots into the grooved rim of wheels.

7-Gear

A gear is mechanism consisting of two wheels with teeth.Example : correction tape

3rd post

Hello we are eva and lidia and this is the third post

Stresses:  Are the physical demands that a body or object must withstand when one or more external forces are applied to it.
These are the basic stresses:

1-Compression : this is a caused by forces acting on a body that tend to flatten it or reduce its length or thickness.It happends in stuctures that need to support weigths.

2-Tenssion: this is caused by forces acting on a body that tend to strech it.

3-Bending: this is caused by forces acting on a element that make it curve or bend.It is done by suporting to the two ends and applying force in the centre as shown in tyhe figure to the right.

4-Torsion: this is caused by forces acting on a body that make it twist.

5-Shear: this is caused by two equal forces applied in opposite that act on lines of action close to each other.Shear stress will tend to cut the material if it cannot twist or bend

Pg 95 ex 12

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

Ballon : elastic 

Empty drinks can : plastic

Window frame : rigid

Clay : rigid

Catapult: elastic

Door : rigid

2nd post

Hello this is our second post.

Structure is a collection of elements arranged in a optimun way to support a body or an object.
here we can see a picture of a well-know structrure:

There are diferents types of structures :

1-Mass structures: These are solid,heavy and very study structure.Exaples include walls,dams.Here you can see an image:

2-Truss structures: These structures are composed of bars that form triangles.They are lightweight and sturdy.Examples include cranes,electricity pylons.Here you can see a image:

3-Frame structures:These structures are formed by columns and beams that act as supporting elements.One example might be the stucture of a builiding.Here youy can see an image :

4-Suspended structures: These are held in place by cables and suspenders atached to sturdy supports.Examples include suspension bridge,tents,markets.Here you can see an image :

Force:is an influence thatcan deform a body o change is 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 foces are applied to it

Presentation

Hello,girls and boys we are eva and lidia and we are going to talk in this blog about structures.
we hope you like this blog!!