Newton’s Laws of Motion
To understand Newton"s laws, we first need to know a little about motion and forces. We describe motion in terms of velocity and acceleration.
You are watching: Speed and direction of motion of an object
Velocity: The rate of change of displacement of an object (displacement over elapsed time) is velocity. Velocity is a vector since it has both magnitude (called speed) and direction. For example, if you drive 10 miles North in 0.25 hours (15 minutes), your velocity is 10 miles/0.25 hours = 40 mph in the northerly direction. For further explanation of vectors click here. 
Acceleration: The rate of change of velocity is acceleration. Like velocity, acceleration is a vector and has both magnitude and direction. For example, a car in straightline motion is said to have forward (positive) acceleration if it is speeding up and rearward (negative) acceleration if it is slowing down. We sometimes refer to negative acceleration as deceleration. 
Force: A force is a push or a pull on an object. 
Newton"s Laws of Motion
First Law: 
An object at rest or traveling in constant, straightline motion (a state of no acceleration) will remain at a constant velocity unless acted upon by an outside force. 
This law is illustrated in the movie below:

Second Law: 
The rate of change of momentum of an object is equal to the net force acting on the object. 
where
is the acceleration of the object and is the net force acting on the object. For more indepth discussion click here.A special case of this law occurs when the net force acting on an object is zero (
). In this case, the acceleration of the object is zero and it continues in its present state of motion in agreement with the 1st Law.Conversely, the 2nd Law tells us that a net or unbalanced force must be applied to an object to change its motion. Because a force is a vector (described by both a direction and a magnitude), the motion of an object can be altered in two ways:
If an unbalanced force is perpendicular to the direction of motion, it can cause the path of a moving object to change direction without altering is speed. This is the case on a merrygoround where passengers move in a circle. In circular motion, the direction of motion is constantly changing (unlike linear motion where the direction is fixed). To continue moving in a circle, merrygoround passengers must hold on tightly (apply an unbalanced force), or risk flying off of the ride.See more: What Class Am I If I Was Born In 2006 ) Vol 1, Grade Placement Rubrics
Example Problem: Cleared for Takeoff 
Third Law: 
For every force in nature, there is an equal, but opposite reaction. 
An example of the third law is illustrated below with two people on skateboards. Andy pushes on Bob in order to move Bob away from him. That is, Andy applies a force to Bob,
. In the process, however, Andy begins moving in the opposite direction. Thus, according to the 2nd Law, a force must have been applied to Andy by Bob (). The 3rd Law states that these forces are equal in magnitude an opposite in direction: