Physics 121
FALL SEMESTER 2016

INSTRUCTOR: Dr. Sharma

msharma102@yahoo.com

Chapter 2: Describing Motion (Kinematics in one direction)

• Kinematics: The description of how objects move.

• Reference Frame: The relevant frame which a measurement is being measured to.

Types of Quantities

1. Scalar Quantity: a quantity with magnitude (value) only.

2. Vector Quantity: a quantity with magnitude and direction.

1. Vector quantities are denoted with an arrow ()

• Distance: The total length of the path traveled between two points.

• Distance is a Scalar Quantity.

• Displacement: The change in position.

•  Displacement is a Vector Quantity.
•  A positive sign before the displacement value ( ) , indicates that the direction is towards (the positive x axis) towards (the east)
• A negative sign before the displacement value ( ), indicates that the direction is towards (the negative x axis) towards (the west)

• Average Speed: Measurement of the total distance an object travels divided by the time it takes to travel this distance.

• Speed is a Scalar Quantity         

• Average Velocity: Measurement of the displacement of an object divided by the total time it took for that displacement.

• Velocity is a Vector Quantity,  Unit:
•  A positive sign before the value of velocity ( ) , indicates that the direction is towards (the positive x axis) towards (the east)
• A negative sign before the value of velocity ( ), indicates that the direction is towards (the negative x axis) towards (the west)

• Important:

• Average Speed Average Velocity  in (magnitude) ,because     (DisplacementDistance)

• Average Acceleration: The change in velocity divided by the time taken to make to make this change.

• Acceleration is a Vector Quantity, Unit:
• Decceleration means: an object is slowing down (the magnitude of velocity is decreasing).
•  A positive sign before the value of acceleration ( ) , indicates that the direction of acceleration is towards (the positive x axis) towards (the east).
• A negative sign before the value of acceleration ( ), indicates that the direction of acceleration is towards (the negative x axis) towards (the west).

• Important:

• When the signs of both acceleration and velocity are (the same) , the object is accelerating.
• When the signs of acceleration and velocity are (opposite) , the object is decelerating.

Kinematic Equations:

Freely Falling Objects:

• Acceleration due to gravity
• We replace   in all of the the kinematic equations.
• Velocity = 0 , when the object is in it’s highest position
• The initial velocity up is equal to the final velocity down (assuming the object begins and ends at the same height above ground)