Sir Isaac Newton and Forces 
Newton's Second Law of Motion
Newton's Third Law of Motion
Force equals mass times acceleration (F=m*a)
When this refers to force, it refers to the net force, or Fnet
The net force is all of the force vectors combined. Sometimes all the forces will cancel out and the net force will be zero.
Mass is the amount of matter in an object, and although it is often confused with weight, they are very different.
Acceleration is the rate at which velocity changes. It is NOT the speed at which an object is moving. Acceleration is often written as m/s^2
Sir Isaac Newton was born in 1642 in England, and was a mathematician, physicist, theologian, and author. He came up with the three laws of motion.
Force is measured in a unit called a Newton, named after Isaac Newton.
1 Newton (N) = 1 kg * m/s^2 (acceleration)
Newton's First Law of Motion
An object at rest will remain at rest, and an object in motion will remain in motion, until acted upon by an outside force.
There are many different types of force. There is net force, but there is also normal force, applied force, force of friction, force of drag, force of gravity, force of tension, and many more.
For every action, there is an equal and opposite reaction
This means that in every interaction between an object, there is a pair of forces acting on the two interacting objects
Normal force is a force that acts on any object that is sitting on a physical surface, perpendicular to the surface it's sitting on. Because Newton's third law states that "for every action, there is an equal and opposite reaction", normal force is the equal (in size) and opposite (in direction) to gravity. This is often represented by free body diagrams.
Force of tension occurs when an object is hanging from a rope, chain, or something similar. It acts similarly to normal force, equal in force and opposite in direction to gravity. When an object is hanging in the air, normal force does not affect it, because it is not on a surface, so tension basically replacees normal force.
The force of gravity is a force that applies in every situation on earth (literally). The force of gravity is 9.8 N. To find the force of gravity on a specific object, you have to know the mass of the object. Fg= 9.8 (m). So, if you have a 50 kg object, the Fg will be 490.
Free Body Diagrams (FBD), are diagrams that represent the forces acting on an object at any one point in time. They only represent a moment, but they show all the forces in that moment. They help to show the equal and opposite forces acting on an object.
If a soccer ball is sitting on grass, and gravity is pointing downwards (toward the center of the earth), with a force of 4.5 N, then the normal force will be pointing up towards the sky (opposite in direction), with a force of 4.5 N (equal in size), because for every action, there is an equal and opposite reaction
Inertia is the tendency of an object to resist a change in motion. In other words, objects want to keep doing what they're doing, The faster an object is moving, the more inertia it has. If you've ever tried to stop a soccer ball that was kicked at you, it's easy, because it's only moving a few m/s. However, trying to stop a car moving 30 mph is a different matter.
In physics, a force is any interaction that, when unopposed, will change the motion of an object
In many situations, a force that is acting on an object is friction. Friction is a force that opposes motion between two surfaces that are in contact, and there are two types of friction, static friction and kinetic friction.
Static friction is determined by the static coefficient of friction and the normal force. Static friction is only really used to determine how much force you need to push an object with to move it.
Kinetic Friction has a different coefficient of friction than static friction, and it is always less than the static coefficient of friction because once an object is moving it is easier to keep it in motion than it is to start it. The force of kinetic friction is determined the same way as static friction, by multiplying the coefficient of kinetic friction by the normal force.
A coefficient of friction is the measurement of the degree of slip resistance of a floor surface, and ranges from 0 to 1. The higher the number, the less slippery the surface. The coefficient of friction is a number that is measured in a lab, and there are thousands, between the many, many surfaces that there are, like glass on wood, and kinetic and static coefficients, which are different.
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this is how to calculate weight, because the definition of weight is "the force of gravity on an object"
When all forces acting on an object are balanced, this is a state known as equilibrium.
Balanced forces are when all of the forces acting on an object cancel each other out, like the FBD to the right. When this happens, it means that an object is either stationary or moving at a constant speed. Since you are given no more information by the free body diagram, you don't know.
Unbalanced forces are forces acting on an object that combine and have a net force that is not zero
The force of drag is a force acting opposite to the relative motion of any object moving with respect to a surrounding fluid, gas or liquid.
The equation for drag is Fd = 1/2 D V^2 Cd A
Force of drag equals one half times density of fluid times velocity squared time coefficient of drag times cross sectional area
The coefficient of drag is similar to the coefficient of friction, in that it is measured in a lab based on the shape of the object
The cross sectional area is the area of an object when you are looking directly at it. For example, the cross sectional area of a bullet is a circle, although the nose is cone shaped, when you look at it head on it is a circle, and this is how the coefficient of drag is determined
The density of fluid varies depending on what fluid it is. For example, the density of water is 1000 kg/m^3, meaning that in one meter cubed of water, it contains 1000 kg of water.
From the side, a cylinder looks like this, (left) but it's cross sectional area looks like this (right)
The Greek letter mu is used to represent the coefficient of friction