A force is a vector quantity with a definite magnitude and a definite direction.  A "'force" can either push or pull an object. 

Effects of Forces: 

Forces can have different effects on objects according to the type of material the object is made of (rigid, elastic etc..):

  • A force could change the state of motion the object (make it move, make it go faster, stop it, or slow it down)

  • A force could change the shape of the object (deform it, resize it, reshape it, break it apart...)


Fundamental Forces:  

These are the fundamental forces known to us:

  • Force of gravity -- a very weak force
  • Strong Nuclear Force -- a very strong force (it holds the particles that make up the atoms together)
  • Weak Nuclear Force -- weaker than the strong nuclear force (it allows certain particles within the atom to be released making the atoms radioactive)
  • Electromagnetic Force -- a strong force (made up of the electrostatic force of attraction between two charged particles at rest, and the magnetic force produced when these particles move)
  • Electroweak Force -- This force is believed to be similar to the electromagnetic force believed to unify the electromagnetic forces and weak nuclear forces

Units of Force:

In the metric, the unit of force is The Newton (the symbol for the Newton is N).  

Measuring forces:

A simple way to measure Force directly is with a spring scale.  The amount of stretch on the spring within the spring scale determines the magnitude of the force.

A spring scale is calibrated in Newtons.  refer to the image below:

noteThe diagram shows a spring scale measuring the force of gravity on a medium-sized apple.  Its mass is about 100 g; its force of gravity is 1.0 N.  Another word for force of gravity is WEIGHT!

spring scaleOne Newton [1 N] is approximately the force of gravity ("the weight") acting on a medium sized apple allowed to free fall under the influence of gravity alone.  The Newton can be defined in more precise terms as the force that will stretch the spring of a spring scale when a 100 g mass is attached to its end.

noteNote: Do not confuse the term Mass with the term Weight.  Although in everyday language they are used to mean the same thing, in Physics we use mass (a scalar quantity) to mean the "amount of matter in an object"; whereas weight is a vector quantity and it measures  the gravitational pull on an object (i.e. The Force of Gravity on an object).