Balanced and Unbalanced

Situation A (below) is a Balanced Free body diagram. It is balanced because all the forces (friction, Fapp, normal force, and gravity) "balance" each other on all sides. Horizontally the force it has the same net force, (between friction and Fapp) and vertically it has the same net force. (Norm and gravity)

Situation B however shows something that is unbalanced. This object is unbalanced because there is friction effecting the object, but no force going the opposite direction with the same amount of force.

Free Body Diagrams

This free body diagram a shows an object. This object could be a chair, a box, or some other thing. I'll say a box.

The forces shown on the diagram are Gravity, Friction, the normal force, and Fapp

Gravity is in the object Because objects always have gravity. (We will assume the box is on earth...)

The normal force is there because the box is actually on a table. The normal force is shown when an object is on a surface because it can't fall or accelerate down.

The Fapp force is there because there is a constant force pushing it to the right. 

The friction is there too, and since it is only "half" of the Fapp, the box is moving.

Vectors and Scalars

Scalar only has size, while Vector is Direction AND size. 

An example of a Scalar quantity is Time.

An example of a Vector is a change in temperature.

Four Forces

I was absent. I will get the notes when I get the chance.

Acceleration

The difference between a sports car and a school bus going from a complete stop to 30mph is huge (like the bus) because the amount of time it takes for the sports car to accelerate to 30mph is a lot less than the bus for many reasons. The bus was meant to hold large amounts of people, but not to race some sports car, which are made to be faster. The acceleration of the sports car will also be faster because they are better with wind resistance then a huge block with 30 people inside of it...

By the way,