phy chap1 moment and position

• Vector quantity : A quantity that has both magnitude and direction is called a vector quantity.


  eg; velocity, force, acceleration, weight
• scalar quantity : A quantity that has only magnitude is called a scalar quantity.


  eg; length, mass, time, temperature, energy, distance, speed
• Speed : Speed is defined as the distance travelled per unit time.


  speed= distance/time
• Velocity : Velocity is defined as the distance travelled per unit time in given direction.


  v=d/t (or) v= s/t
• speed - instantaneous speed, average speed
• Acceleration : Acceleration is change in velocity per unit time.


  a= change in velocity/time (or) a= v-u/t
• gradient = rise/run = distance/time = speed
• Average speed : Average speed is found dividing the total distance, a body has travelled by the time, it has taken.


  speed may vary from moment to moment during this time.
• Instantaneous speed : Instantaneous speed is the speed at which the body is traveling at a moment in time.
• average speed = initial velocity+ final velocity/2
• Newton's First Law : "If net force = 0 then acceleration = 0".


  if no net external force acting upon a body, a particle at rest will remain at rest and a particle in motion at a constant velocity will continue to move with the same constant velocity . So there is no acceleration.
• Newton's Second Law : The net external force acting upon a particle is equal to the product of the mass and the acceleration of the particle.


  F=ma
• Friction : The force between two contact surface that acts to resist the motion of the body is called the friction
• v= u + at


  v² = u² + 2as
• s = ut + 1/2at²
• Drag : Object experience friction when they move through a liquid or a gas. This force is called drag.