Dynamics

The study of dynamics goes beyond the relationships between the variables of motion as illuminated in kinematics to the cause of motion, which is force. 

Newton's Laws of Motion

1. Newton's first law of motion, also called the law of inertia, states that an object at rest will stay at rest while an object in motion will stay in motion unless acted on by an external force. 
2. Newton's second law of motion states that if a net force acts on an object, it will cause an acceleration of that object. This law addresses the cause an effect relationship between force an motion commonly stated as F=ma. Force is measured in Newtons (N). 
3. Newton's third law of motion states that for every action there is an equal and opposite reaction. 

Mass and weight are different physical quantities. Mass is the measure of the amount of matter in an object.The force that the Earth exerts on an object of specific mass is called the object's weight. The expression for weight is W=mg, where g is acceleration due to gravity.

Free-body diagrams also called force diagrams are used to help better understand the relationship between force and acceleration in a particular case.  

                                 
Friction is the force opposing the motion of one body sliding or rolling over the surface of second object. There are two main types of friction: static and kinetic friction. 

1. Static friction is the force of friction when there is no relative motion between two objects in contact, such as a block sitting on an inclined plane. The magnitude of the frictional force is 
   F_s ≤ μ_s N,. 
2. Kinetic friction is the force of friction when there is relative motion  between two objects in contact. The magnitude of the friction force in this case is F _k ≤ μ_k N.

                         Applications in Real-Life

Ice Skating

Tides 

                             References:
http://www.cliffsnotes.com/study_guide/Dynamics.topicArticleId-10453,articleId-10417.html