Motion, Speed, Motion, Speed, Velocity and Velocity and AccelerationAcceleration

VECTORS AND SCALORSVECTORS AND SCALORSORIGIN - POINT AT WHICH BOTH ORIGIN - POINT AT WHICH BOTH VARIABLES ARE AT 0 (ZERO)VARIABLES ARE AT 0 (ZERO)

MAGNITUDE – SIZEMAGNITUDE – SIZE

VECTORS – DIRECTION (represented by VECTORS – DIRECTION (represented by arrows)arrows)

SCALARS – QUANTITIES W/OUT DIRECTION SCALARS – QUANTITIES W/OUT DIRECTION (ex distance m, time s, temp C) (ex distance m, time s, temp C)

RESULTANT – SUM OF VECTORSRESULTANT – SUM OF VECTORS

6m east plus 2 m east = 8m east6m east plus 2 m east = 8m east►Resulatant subtracting vectorsResulatant subtracting vectors

►A - B = A+(-B)A - B = A+(-B) A = 20 m westA = 20 m west B = 5 m eastB = 5 m east

15m15m

Time Interval/DisplacementTime Interval/Displacement

►Time interval - change in time =final Time interval - change in time =final time –initial time ….time –initial time ….

►formulaformula

►Displacement - Change in distance = Displacement - Change in distance = final distance – initial distancefinal distance – initial distance

►formulaformula

MotionMotion

►MotionMotion – an object’s change in – an object’s change in position relative to a reference pointposition relative to a reference point

Reference PointReference Point

►The Earth’s surface is used as a The Earth’s surface is used as a common reference pointcommon reference point

►A moving object can be used as a A moving object can be used as a reference point as wellreference point as well

SpeedSpeed

►SpeedSpeed is the distance traveled divided is the distance traveled divided by the time interval during which the by the time interval during which the motion occurredmotion occurred

►Normally, objects do not travel at a Normally, objects do not travel at a constant speedconstant speed

►Average Speed - Average Speed - total distancetotal distance

total timetotal time

Which Distance?Which Distance?

► Farmer Jones drives 6 miles down a straight Farmer Jones drives 6 miles down a straight road. he turns around and drives 4 miles road. he turns around and drives 4 miles back. What was his average speed for this back. What was his average speed for this trip if it took 1 hour?trip if it took 1 hour?

                                            

              

Your answer to this problem Your answer to this problem depends on your interpretation of depends on your interpretation of "distance traveled". You could say:"distance traveled". You could say:

► The The total distancetotal distance traveled by Farmer Jones is traveled by Farmer Jones is 10 miles. Therefore his average speed is 10 mi/hr. 10 miles. Therefore his average speed is 10 mi/hr.

► The The net distancenet distance traveled by Farmer Jones is 2 traveled by Farmer Jones is 2 miles. Therefore, his average speed is 2 mi/hr. miles. Therefore, his average speed is 2 mi/hr.

► There are good reasons to use either There are good reasons to use either interpretation - it's mostly a matter of preference. interpretation - it's mostly a matter of preference. We will interpret "distance traveled" to be We will interpret "distance traveled" to be net net distancedistance ( (also calledalso called displacement).displacement). Farmer Farmer Jones' average speed was 2 mi/hr.Jones' average speed was 2 mi/hr.

VelocityVelocity

►VelocityVelocity is the speed of an object in a is the speed of an object in a particular directionparticular direction

► Imagine two birds leave the same tree Imagine two birds leave the same tree at the same time. The both fly at at the same time. The both fly at 10km/hr for 5 minutes. Why don’t 10km/hr for 5 minutes. Why don’t they end up at the same place?they end up at the same place?

VelocityVelocity

►VelocityVelocity appears to be very similar to appears to be very similar to speed, however, when describing the speed, however, when describing the velocity of an object you need to velocity of an object you need to provide a magnitude and a directionprovide a magnitude and a direction

►MagnitudeMagnitude – the speed of the object – the speed of the object►DirectionDirection – the direction the object is – the direction the object is

movingmoving►Pg 43 demoPg 43 demo

VelocityVelocity

►Ex) A bus has a velocity of 35miles/hr Ex) A bus has a velocity of 35miles/hr heading westheading west

Resultant VelocityResultant Velocity

►An object can have a resultant velocity An object can have a resultant velocity if it is experiencing more than one if it is experiencing more than one motion.motion.

►For example if a person walks down For example if a person walks down the center of a bus while it is in motion the center of a bus while it is in motion there are two velocities occurring.there are two velocities occurring. 1. The movement of the bus1. The movement of the bus 2. The movement of the person inside the 2. The movement of the person inside the

busbus

ExampleExample

15 m/s + 1 m/s = 14 m/s

ExampleExample

15 m/s + =1 m/s 16 m/s

AccelerationAcceleration

►AccelerationAcceleration is the rate at which is the rate at which velocity changes over timevelocity changes over time An object accelerates if its speed, direction, An object accelerates if its speed, direction,

or both changeor both change

►Average acceleration = final velocity – starting

velocitytime it takes to change

velocity

AccelerationAcceleration

►ExampleExample A car on the highway is traveling 55 mi/hr A car on the highway is traveling 55 mi/hr

and it passes another car. In order to and it passes another car. In order to pass, the car has to accelerate to 65 pass, the car has to accelerate to 65 mi/hr. The car reaches this velocity 40 mi/hr. The car reaches this velocity 40 seconds later. What is the average seconds later. What is the average acceleration of the car?acceleration of the car?

Acceleration and VelocityAcceleration and Velocity

►As velocity As velocity increasesincreases, so does , so does accelerationacceleration

►As velocity As velocity decreasesdecreases, so does , so does accelerationacceleration

►When direction changes, so does When direction changes, so does accelerationacceleration

►When there is a When there is a constant velocityconstant velocity, , there is no accelerationthere is no acceleration