1. UNIT 2 MECHANICS
CHAPTER 4 KINEMATICS

2. Chapter 4A – Introduction to Mechanics

3. Historical Development of Mechanics
Make sure to READ when answering your homework questions!!
Mechanics
The scientific study of forces and motion, which consists of kinematics, dynamics, and statics
Kinematics
The science of describing how things move
Involves measurements and calculations of position, time , velocity, acceleration, and displacement
Dynamics
Study of how forces affect an object’s motion
Newton’s three laws for the basis of dynamics
Statics
The description of how stationary objects react to pushes and pulls

4. Physical Systems
In science, scientists must first clearly define what they are going to study.
They need a boundary
Everything in this boundary is called the system
Everything outside this boundary is considered the surroundings
Most of the time scientists are interested in how the surroundings affect the system

5. What should our frame of reference be?
Frames of Reference
Point of reference
A stationary location from which we choose to make our observations
Frame of reference
Geometric space containing the point of reference, also called the reference frame
What should our frame of reference be?
The Bible

6. Kinds of Reference Frames
Fixed reference frame
The system is in motion
Accelerated reference frame
The system is not moving at a constant motion, it is accelerating
Rotational reference frame
The system is revolving
Coordinate axis
An imaginary line that contains an origin as a point of reference and is marked off in distance units
One dimensional

7. Time Intervals/Scalars and Vectors
A span of time during which a phenomenon is observed, calculated by subtracting the initial time from the final time
Always a positive value
t = Tf Ti
Delta tee
Scalar
Any measurable quantity that can be completely described with a single piece of information
Positive, negative, or zero
Represented by an italicized symbol
Vector
Represented by a bold symbol or a half arrow above the scalar symbol
Requires two pieces of information to describe them completely, scalar value and a direction

8. Chapter 4B – Kinematics: Describing Motion

9. Kinematics only deals with how an object moves
What is Motion?
Kinematics only deals with how an object moves
Measures positions, speed, velocity and acceleration
We need to describe how things move before we can explain the causes of the motion

10. Distance and Displacement
A positive scalar quantity representing the linear dimension a moving object covers during a time interval
Displacement
A vector quantity that describes the net distance and direction of motion
Magnitude
The size of any quantity expressed as a positive number in appropriate unit

11. Formula: speed = distance/time (average speed)
Speed and Velocity
Speed
Rate of motion of a system
Magnitude of velocity
Always a scalar quantity (no direction)
Represented by symbol v
Always positive
Formula: speed = distance/time (average speed)
v = d t

12. Speed and Velocity Velocity
The rate of displacement of a system
Vector quantity
Represented by v
Formula: velocity = displacement/time interval (not necessarily distance)
v = d t

13. Calculations
Make sure you use significant digits!
DON’T PEAK at the answers!!!
Example 4-1 (pg 82)
Example 4-2 (pg 83)
Example 4-3 (pg 83)

14. Formula acceleration = velocity/time a =
The rate of change of the speed or velocity during a given time interval
Vector or scalar
Formula acceleration = velocity/time
a = v t

15. More Calculations
Example 4-4 (pg 84)
Example 4-5 (pg 85)

16. Motion in Two and Three Dimensions
Our study in this course will only be one dimensional
Motion in real life is two or three dimensional
Two dimensions (x, y)
In a plane
Players on a soccer field, cars on a road, ships on the ocean (horizontal)
Thrown ball, falling bomb (vertical)
Three dimensions (x, y, z)
Occurs in all three spatial dimensions: length, width, and height
Roller coaster, aircrafts, thunderstorms
Definitions are the same, math more complicated (trigonometry)
You will study this in physics