UNIT 2 MECHANICS CHAPTER 4 KINEMATICS

Chapter 4A – Introduction to Mechanics

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

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

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

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

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

Chapter 4B – Kinematics: Describing Motion

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

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

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

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

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)

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

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

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