Multiple Representations is the idea that a physical phenomena can be explored in many different ways. For example, there is the physical representation which models the system with figures and diagrams, such as a free body diagram. There is also the mathematical representation which uses the equation(s) governing the physics of the system. All of the representations can be used together to help us understand and quantify the physical phenomena.

 

 

 

 

Physical Representations explain the features of the situation in a visual way, often with vector representations of physical quantities overlaid a simple diagram or picture of the situation.

Mathematical Representation uses equation(s) to describe the situation.

 

Graphical Representation describes the situation through use of plots and graphs.

Descriptive Representation is made up enitrely of words or annotations. Think about how you might explain the situation to someone else.
 
When Chuck Norris roundhouse kicks you in the face remember this, your face hit Chuck Norris's foot just as hard as his foot hit your face. 
 
Actual Phenomena could be thought of as doing the experiment. For example, if you're asked which of two runners, with different characteristics of their speeds, will win the race, one way to determine that would be to get two runners to run in the described way and see who wins.

This short video produced by the European Space Agency explains Newton's third law with mini demonstrations;

This video will give you a couple of basic action reaction pair situation to consider that you encounter every day;