We get the concept of Balanced and Unbalanced force from Newton’s Laws of Motion. 1st Law of Motion states that –An object continues to be in its state of rest or of uniform motion in a straight line until some unbalanced force is acted upon.
Force acting upon in a body is either balanced or unbalanced. Let us explain with an examples of balanced forces -
Image of Balanced force
Place a Brick on a table. Apparently we don’t find any force acting on that brick when it is at rest. But fact is that there are two forces acting upon that brick.(a) Gravitational force is pulling downward –F2 (b) the force of the table in upward direction +F1.
The resultant force acting on the book is
FR = +F1+ (-F2)
= +F1 – F2
These two forces balance each other so the brick can be at rest position. This is called equilibrium position.
Image of Unbalanced force
If you push the brick the brick starts moving .Now one more force is working on the brick that is unbalanced force. Due to this unbalanced force book changes its state. So this is not in equilibrium position. This unbalanced force causes friction and acceleration. This unbalanced force exerts opposite direction of book’s movement. One more practical example of balanced and unbalanced force is tag war .When both of the team have equal strength the rope mostly stays in same place. Because no unbalanced force is there and resultant force is zero.
But when one team wins in tug of war then there must be an unbalanced force present.As we know that unbalanced force causes change in motion.
F2 `>` F1
So the resultant force is F2
A bullet of mass 0.07 kg moving with a speed of 50m s-1 enters a heavy wooden block and stopped after a distance 50 cm. What is the average unbalanced force exerted by the block on the bullet?
Solution: The retardation of bullet is,
By 2nd law of motion the retarding force will be
= 0.07X 100 Kg m s-2
= 7 N
Check this topic Equations for Force it may help you to solve your physics problems.
Till now we have discussed that unbalanced force should be in opposite direction. But it can be in same direction also. If you and your friend push a big table the resultant force will be the sum of the forces and in the same direction. Actually two unbalanced force (one is your and another is your friend) is acting on that table.