Chapter 2 Linear Motion

CHAPTER 2

Linear Motion

Learning outcomes

The student will be able to:

·         1.Understand the concept of linear motion

·        2. Define linear motion, uniform and non-uniform motion

·         3.Describe distance, displacement, speed, velocity, average velocity, acceleration and deceleration.

·        4. Apply the concept of linear motion in solving the related problems.

·         5.Illustrate velocity-time graph.

·        6. Determine the velocity, acceleration and displacement from the graph

     INTRODUCTION

      Motion is the process of something moving or changing place, or even just changing position. There are a lot of factors involved every time something moves. There are fewer factors involved if an object moves at the same speed in a straight line. However, most movement involves changing the speed of the movement and changing directions.

     If the position of a body is not changing with respect to a coordinate system and the set of physical reference points, the body is said to be at rest, motionless, immobile, stationary, or to have constant position. An object's motion cannot change unless it is acted upon by a force.

      Linear motion is the motion that is natural to an object: moving in a straight line in one direction. The direction can either be in a horizontal, vertical or inclined direction. Linear motion can be uniform or non-uniform motion.

     Uniform Motion is movement in a straight line at a constant velocity or a body is said to have a uniform motion if it travels equal distances in equal intervals of time, no matter how small these intervals may be. The uniform motion according to Newton’s First Law is a body with no net force acting on it will either remain at rest or continue to move with uniform speed in a straight line.

       Examples of uniform motions 

A car moving in a straight line at a constant speed

A moving bullet

A train going along the tracks at   steady speed

A ship steaming on a straight course at steady speed

      Examples of non uniform motions 

A roller coaster ride

Throwing a softball

 A crawling snake

 A racing horse

     DISTANCE AND DISPLACEMENT

      Distance is simply the total path length traversed in moving from one location or point to another. Distance is a scalar quantity because it has magnitude but no direction. It is always positive. 

     Displacement is the distance between two locations measured along the shortest path between two points in a specified direction. Displacement is a vector quantity because it has magnitude and direction.

	Distance	Displacement
Definition	Total path length traversed in moving from one location or point to another	The shortest path between two points in a specified direction.
Quantity	Scalar	Vector
SI unit	Meter (m)
Symbol	d	s

      SPEED AND VELOCITY

   

    Speed is a physical quantities which measure how fast an object is moving or rate of change in distance.

      Speed is a scalar quantity. It’s SI unit is meter per second or ms^-1 @ m/s and symbolized as v.

      Velocity tells you how fast and in what direction an object moves. It is can also be defined as rate of change of displacement. Velocity is a vector quantity. It’s SI unit is meter per second or ms^-1 @ m/s and symbolized as v.

	Speed	Velocity
Definition	Speed is a physical quantities which measure how fast an object is moving or rate of change in distance.	Velocity tells you how fast and in what direction an object moves orrate of change of displacement.
Quantity	Scalar	Vector
SI unit	Meter per second (ms-1)	Meter per second (ms-1)
Symbol	v	v

      ACCELERATION AND DECELERATION

     Acceleration is defined as the rate of change of velocity. Average acceleration is equals to the change in velocity divided by the time taken to make the change. It's SI unit for acceleration is  ms^-2 @  m/s.² 

      Acceleration is a vector quantity and symbolized as a.

	Acceleration	Deceleration
Definition	Acceleration is rate of change of velocity. It's mean final velocity is greater then initial velocity	Deceleration  is rate of change of velocity. It's mean initial velocity is greater then final velocity
Quantity	Vector	Vector
SI unit	Meter per second2 (ms-2)	Meter per second2 (ms-2)
Symbol	a	-a
Others	Positive value	Negative Value

      EQUATION OF LINEAR MOTION 

      

v² = u² + 2as

s = ut  +  ½ at²

v =  u  + at

s = ½ (v + u ) t

     MOTION IN GRAPH

     Velocity-time graph