*attractive force- the attraction of a negatively charged object with a positively charged object.

*repulsive force- the repulsion of two objects with the same charge. 

*propulsion- the use of force to drive an object forward.  

*friction-  a force that resists the movement of objects.  It occurs when any two objects make contact.  

*Newton's First Law of Motion- states that an object in motion will remain in motion and an object in rest will remain ant rest until an outside force acts upon it.  

*sliding friction- the type of friction that occurs when any two surfaces slide over each other.  

*rolling friction- the friction produced when an object roles over a surface.  

*aerodynamics- the study of how objects move through gases, especially in the atmosphere.   

*drag- the force that opposes the movement of an object through a fluid.  

*streamlined- to be designed with the least amount of resistance to fluid flow.  

*Newton's Third Law of Motion- states that for every action there is an equal and opposite reaction.   

*Kinetic Energy- the energy of motion.  it can be calculated as;  

*Potential Energy- stored energy that has the potential to do work.  It is associated with position. 

*poles- the two ends of a magnet where the magnetic force is greatest.

*mass- the amount of matter contained in a object. 

*acceleration- a change in velocity. 

*gravity- a force of attraction between all objects in the universe, especially the attraction between earth and the objects near its surface.