Frictional force : opposes the relative motion between the contact surfaces of the objects. It is major necessity in our daily life such as writing on a paper(friction is present between the surface of pencil and paper through which it make possible to write) , friction facilitate us to walk , holding a glass of water,etc., These are all possible acts due to friction present. Friction can be acts as evil if we consider the amount of loss of energy in any process such as , the wear-and-tear of the tires of vehicles on the road during motion is due to friction, pushing of the heavy objects on the rough surface makes it difficult to move due to friction present. ★ So, overall we can say that friction is the necessary evil in the human life.

Salesforce is a leading CRM (Customer Relationship Management) software which is served form cloud. It has more than 800 applications to support various features like generating new leads, acquiring new leads, increasing sales and closing the deals. It is designed to manage the organization's data focused on customer and sales details. It also offers features to customize its inbuilt data structures and GUI to suit the specific needs of a business. More recently, it has started offering the IOT (internet of things) connectivity to the CRM platform.

Salesforce is a vast topic, so the tasks of a Salesforce Developer are equally varied.

A developer might: 

Customize the Salesforce environment to customize it for his/her client/customer. Integrate with other systems. Works on mobile or website applications. Develop apps to make lives for other Salesforce developers easier. 

Not necessary that the person works for Salesforce.com: The Customer Success Platform To Grow Your Business, Now lot of people say that they are Java Developers, do you think they work for Java ?

Its just that we are working on technology developed by Salesforce.