A while back I posted on the force differences between various magnitudes of earthquakes. When you start throwing numbers and math around many lose interest pretty quickly.
Here is another way of looking at it.
For comparative purposes only, if a strong man was holding a stack of 4 cars over his head representing the 4.2 earthquake this afternoon ( I have no idea how to convert the actual force of a 4 into a specific number of cars so don't worry about it).
To this strong man's right, is another man holding a stack of cars equal to a magnitude 6 earthquake, that man would be holding a stack of 800 cars over his head. A 6 is roughly 200 times more forceful than a 4 (4 cars X 200 times more force = 800 cars). A 4 is 200 times more forceful than a 2. An 8 is 100 times more forceful than a 7 and 800 times more forceful than a magnitude 1 (as a generalization).
Remember this is not a doubling or tripling of force as in a 100% or 200% increase (double = 100% triple = 200% etc), it is and actual multiplication of the of the overall force as if you added 200 separate but equal earthquakes together to get a total.
If you are close enough, and concentrating you can feel a 3. You can definitely feel a 4 and you don't have to be paying particular attention before you notice it. You will absolutely feel a 5 and at about 5.3 or so, you might even be able to hear the rumble of the seismic waves. At 6, it becomes harder to maintain your balance but you probably won't fall over. You watch pictures fall off the walls, cupboard doors swing open and you should have good sized waves in your swimming pool. 7 and above, you are probably going to sit down before you fall down because standing will be very difficult. Furniture will move across the room, stuff falls out of cupboards, support structures crack and collapse due to shaking and not being able to support the weigh any longer, and lots of other not so nice things.
Shake duration is also significant. Obviously a force applied to objects for 10 seconds has less of an effect than that same force being applied for 30 seconds or a minute. Shaking can and has lasted for a very long time (relatively speaking). In some strong earthquakes continuous shaking for 2 or more minutes is not unheard of. All of the quakes that have occurred here in the DR in the last 4 years have all lasted less than 12 seconds and this is indicative of load shifting within the ground and fault line equalization - lots of little shifts to even the stress out over a greater distance. When this pressure equalization process is no longer effective, then after a period of stress buildup, there is a rupture and that produces a big one.