Force moves the sales process forward. Areas of force include accurate and timely information, a good understanding of the problem, your ability to listen and overall responsiveness. Friction slows down the sales process. Essentially, when your prospect has to jump through too many hoops or faces obstacles or inconveniences throughout the sales process, this creates friction which makes your job more difficult.
Audible is an Amazon-owned producer of audiobooks and spoken-word entertainment. This platform builds awareness and brings potential subscribers into their sales funnel by partnering with authors of books featured on the platform to promote their audiobook using a free one-month trial for the service. When users sign up for the free trial, they are given 30 days to use the service before being automatically enrolled in a monthly subscription.

The marketing funnel depicts the steps of a hypothetical buyer through his decision-making process. The funnel is widest at the top and then gradually grows more narrow. The earliest models depicted a customer entering the funnel as a novice and then sliding down the funnel and through the steps of awareness, interest, desire and action, meaning a purchase.
For example, when a customer finds you organically through a Google search for example, that means you have some element of authority. When you have authority, prospects are more likely to enter into your funnel because they know that if they found you relevantly, that whatever it is that you're providing must be of a great value. That's just the nature of SEO and organic search. 
Entry sources – Monitoring the sources from which people are entering your funnel can be useful data to track, as it gives you ideas for expanding the reach of your marketing campaigns. If, for example, you see that a large number of your prospects are coming from a single guest blog post you did, you can upgrade and expand on it, add a free consultation opportunity on that blog post, and/or find similar guest author positions.

In marketing automation, Ryan Deiss, co-founder of Digital Marketer, often describes the sales funnel as a multi-step, multi-modality process that moves prospective browsers into buyers. It's multi-stepped because lots must occur between the time that a prospect is aware enough to enter your funnel, to the time when they take action and successfully complete a purchase.