Force and Motion

What is Force?

A push or pull upon an object resulting from its interaction with another object, that can start or stop motion or deform an object.

Represented by \(\vec F\).

Nature of force

• Vector quantity
• SI unit is Newton (N). Other unit is dyne. 1 N = 100,000 dynes.

Types of Force

1. Contact Forces – through physical touching
   • Frictional Force: Opposes the relative motion of two surfaces in contact.
   • Tension Force: In a string, rope, or wire when it is pulled tight by forces acting from opposite ends.
   • Normal Force: Support force exerted upon an object in contact with another object.
   • Applied Force: Force applied to an object by a person or another object.
   • Air Resistance Force: Frictional force that acts upon objects while travelling through the air.
2. Non-Contact Forces: without actual touch between objects.
   • Gravitational Force: Attraction between any two objects with mass.
   • Electromagnetic Force: Force arising due to electric and magnetic fields.
   • Nuclear Forces:
     • Strong Nuclear Force: Keeps particles together in the nucleus of an atom.
     • Weak Nuclear Force: Responsible for radioactive decay.

Combination of forces

Action of multiple forces on a given object produces an effect which is equivalent to effect produced by a single force in magnitude and dimension. The single force is called as resultant force of all the applied forces. Resultant force is vector sum of all the forces applied. Resultant force is symbolized as \(\vec{F_{net}} = \vec{F_1} + \vec{F_2} + \vec{F_3} + … \vec{F_n} \)

Balanced and Unbalanced Forces

• Balanced Forces: group of forces which cancels effects of each other and there is no final effect on the object. Resultant force is zero. \(\vec{F_{net}} =0\). In this situation, the object is said to be in equilibrium.
• Unbalanced Forces: group of forces which produces a net effect on the object’s motion, shape etc. Resultant force is not zero. \(\vec{F_{net}} \neq 0\)