Engineering Mechanics Article:- 1

Basic of Engineering Mechanics

  Engineering mechanics is a very interesting subject. It is so important for engineers that I would even go the extent to say that if you know the basic mechanics, you are almost an engineer. 

    Engineering Mechanics of rigid body can be divided into three main parts

• Statics, 
• Dynamics 

Engineering mechanics focuses on the study of response of bodies under the action of forces. 

• What do these words mean ?
• What are bodies? 
• What is a response?
• What are forces?

What are bodies?  

    Bodies can be anything. It may be a table or a gadget or a building or an aircraft wing. 

What is a response?

Response means how bodies react when you apply forces.

For example, think of a chair. A chair maybe designed to withstand, 150kg . A man weigh 70 kg. So there is no problem if he sit on it. But if you overload the chair it may break. This is the response from the chair when a force is applied. 

There is always a response. But sometimes you can see and feel the response because it is large. Sometimes you don’t see because the response is small. 

For example, consider a rubber band. If you pull this, it expands. You can see the response of the rubber band under the action of the force that you are applying. It responds by increasing its length. So bodies are any objects that we want to study. Response is how bodies react when forces are applied. Now that we have a better understanding of bodies and the response, It is time for us to develop an understanding of forces.

What are forces? 

You probably have heard a simple definition of a force as early . It is stated as: Force is a push, or a pull. This simple definition is still true and we will continue to use it. 

For simplicity we can classify forces into two categories: 

• Contact forces 
• Non-contact forces. 

1.Contact forces
As the name implies contact forces occur when two bodies are in physical contact. For example, the force that you was applying on this rubber band is a tensile force.

Contact forces are 

• Tension forces 

    The forces acting away from each other are Tensile Forces. The force that balances the force applied on it. It acts on ropes or string. When the string is stretched due to application of some force, a force of tension is developed in the string, which counters the effect of action force. This force is also equal and opposite to action force. e.g. stretching or straightening of rope during tug of war.

• Compression forces

    The forces acting towards each other are compression forces.

• Normal forces

    Any Applied force

• Friction forces

The force which acts between the two surfaces in contact, which opposes the relative motion in between them. e.g. a ball comes to relative rest after rolling for some time.

• Spring forces

    Also know as restoring force, is the force that enables elastic bodies to restore their original shapes. e.g. a compressed spring comes back to its original state when the external force is withdrawn.

• Air resistance forces

    The force acts by air resisting to the movement of object.

• and any applied force. 

2. Non-contact forces are weight, which is a gravitational force, electric forces and magnetic forces. There are also strong nuclear and weak nuclear forces. They play an important role in quantum mechanics.

Let us talk a little bit more about forces & reaction. What If you apply a force on the wall, 

What happens? 

You can see applying a force but there is no visible change in the wall. Wall is not moving and it is staying, where it was. 

So what’s happening? 

The force that applying is being resisted by the wall, and that’s why the wall is not moving. This resistance force, or reaction force is equal and opposite to the force applied. So there are two forces here. The force that applied. The reaction force from the wall. I can extend this logic to our weight. Realize we are standing on the floor. This means our weight is pushing onto the floor. If the floor is not pushing back, then we will not stay on the floor. We will keep falling. Can you imagine that? So I can say force does not exist alone. Forces always occur in pairs. So now that we have developed the definitions for body, response and forces. We will continue it in next article