Hello,
To my Dearly appreciated Readers,

May I wish you a wonderful day amidst the chaos of the year.

Now, on to the point of my blog, let me address the concept of today. This post will discuss free body diagrams, as well as the parts that make them up.

Concept 1: Force diagrams (AKA Free body Diagrams AKA FBD's)

What are force diagrams?

Well, they are the diagrams that explain how the forces (such as tension, gravity, pull, push, and friction) interact with objects on our planet. A free body diagram is composed of multiple parts. The central part is a dot or circle, which represents the item that forces are acting upon, and only that one item.
Please note the example below:

Image taken from: wikipedia

The f weight in this example ends up actually being Fg in all that we do, however it does show us what a free body diagram looks like for an object sitting at a table


 On our planet, the force of gravity is labeled as g= 9.81 (or less precisely 10).

Concept 2: newton's 1st law.

There are three laws that govern forces as we know it  so far, but we have only covered 2. These laws are Newton's 1st law, and Newton's 3rd law.

Newton's 1st law is that "An object at rest stays at rest and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced force." (physics classroom.)

This means that any object such as a ball, a bike, anything really wants to do what it is currently doing. This means that any object moving will stay moving but any object that is not moving (at rest) will stay at rest. The only exception is if an outside (aka unbalanced) force acts upon it which means that something affects it such as pushing or pulling, blowing, moving it, etc...

This applies to life in that a ball won't move unless you touch or kick it, a ball won't fly through the air unless you throw it. 

In fact , a ball flying through the air is only affected by one force the whole time, that is the force of gravity. From the start of the throw the ball goes through 3 stages, going up, being perfectly in the middle, and coming down but no matter what the only aspect that matters is that gravity is the only thing acting on it. 
Thus the free body diagram is:

In another example, a skydiver is also only affected by gravity until they open their parachute up. In the first few seconds, the speed of the man is steady, but once they open their parachute, their descent slows  as the air resistance of the parachute starts to try and counter-balance gravity. Thus we see the chronicle of events, with first their initial jump from the plane, then when they have just opened their parachute but it is not fully expanded, to when it has slowed their descent considerably but not halted it.

All objects on the earth, at rest, or experiencing constant velocity have balanced forces. The FBD for at rest and at constant velocity look the same. They are shown below. 

Concept 3. 
The relationship between mass and weight (g=9.81n/ kg but we tend to use 10 for basic problems).

Weight in Newtons is the result of mass times the force of gravity. This is depicted in the formula:
w=mg.

We tend to use 10 for the force of gravity, but the exact number allowed is 9.81. Mass is only taken in kg thus any weight in grams must be multiplied by .01 to then become in kilograms which we can convert to newtons.

Thus if an object has a mass 2.5 kg, we can solve for weight by inserting the mass into our formula (w=mg) as w=10*2.5 or alternatively w=2.5*10.
Thus weight equals 25 newtons for the object.



Concept 4. Friction force and normal force on objects.
Friction force is the force that stops us from endlessly accelerating from one single push, as it helps slow us down. Normal force is what is counter to gravity, stopping us from sinking straight into the earth.

Friction is affected by surface material and weight, surface area doesn't matter.


Concept 5. Here is an example of a balanced force diagram. The umbrella is perched atop the bike and weighs 40 newtons. The bike weighs 200 newtons. The action reaction pairs are:

found via google images, umbrella on bike.

The umbrella 

Umbrella pulls bike up.
Bike pulls umbrella down.

Bike pulls earth up.
Earth pulls bike down.


The formula for an action reaction pair is:
Object 1 exerts force on object 2 in a direction.
Object 2 exerts equal force on object 1 in opposite direction.