Kinematics Motion Day 1

Frame of Reference The object or point from which movement is determined A. Movement is relative to an object that appears stationary B. Earth is the most common frame of reference Using clip from movie, Top_Secret_Train_Station_Gag.mp4Top_Secret_Train_Station_Gag.mp4

Scalar versus Vector Scalar - magnitude only (e.g. volume, mass, time) Vector - magnitude & direction (e.g. weight, velocity, acceleration)

Pictorial Representation An arrow represents a vector – Length = magnitude of vector – Direction = direction of vector This arrow could represent a vector of magnitude 10 point to the “right”

Speed is a Rate In this case, rate implies a time dependence. Examples: – The number of laps you swim per hour – The number of times you sneeze per day – The number of vacations taken per year So speed is defined as the rate of motion With our definition of motion we have: Speed = rate of change in position

Speed The average speed of an object is defined as the total distance traveled divided by the total time elapsed – Speed is a scalar quantity

Velocity The average velocity of an object is defined as the total displacement traveled divided by the total time elapsed – Velocity is a vector quantity

Speed, cont Average speed is the total distance divided by the total time SI units are m/s

Velocity It takes time for an object to undergo a displacement The average velocity is rate at which the displacement occurs generally use a time interval, so let t i = 0

Velocity continued Direction will be the same as the direction of the displacement (time interval is always positive) + or - is sufficient Units of velocity are m/s (SI) Other units may be given in a problem, but generally will need to be converted

Acceleration Change in velocity divided by the change in time

Acceleration Changing velocity (non-uniform) means an acceleration is present Acceleration is the rate of change of the velocity Units are m/s 2 (SI), cm/s 2 (cgs), and ft/s 2 (US Cust)

Average Acceleration Vector quantity When the sign of the velocity and the acceleration are the same (either positive or negative), then the speed is increasing When the sign of the velocity and the acceleration are in the opposite directions, the speed is decreasing

Kinematic Equations Used in situations with uniform acceleration Homework: Rearrange each equation to solve for the other variables