What is speed?What is speed?

Watch the toy car: (pull back car)Watch the toy car: (pull back car) What did you see?What did you see?

The car changed positions.The car changed positions. How does what you saw define the term How does what you saw define the term

SPEED?SPEED? How fast an object is moving or changing How fast an object is moving or changing

positions.positions. Speed is the rate at which distance is covered.Speed is the rate at which distance is covered.

Why is speed referred to as a RATE?Why is speed referred to as a RATE? Rate is a clue that something is changing in a Rate is a clue that something is changing in a

time period.time period. Heart rateHeart rate Interest rateInterest rate Dropout rateDropout rate

What is a SCALAR QUANTITY?What is a SCALAR QUANTITY? A quantity in which direction is either n/a or A quantity in which direction is either n/a or

not specified.not specified. temperaturetemperature

What are the units of speed?What are the units of speed? any distance unit / any time unitany distance unit / any time unit

mphmph km/hkm/h cm/daycm/day

What are the most common units we will What are the most common units we will use for speed?use for speed? meters per second m/smeters per second m/s kilometers per hour km/hkilometers per hour km/h

Examples of speeds:Examples of speeds:

km/hkm/h mphmph m/sm/s2020 1212 664040 2525 11116060 3737 17178080 5050 2222100100 6262 2828120120 7575 3333

The speed equationThe speed equation:: In words:In words:

speed=distance / timespeed=distance / time In symbols:In symbols:

s= d/ts= d/tThe wheel:The wheel:

Cover the unknownCover the unknown

ds t

Let’s look at other types of Let’s look at other types of speed:speed: How can you tell a car’s speed at a How can you tell a car’s speed at a

given instant in time?given instant in time? look at the speedometerlook at the speedometer

What is this type of speed called?What is this type of speed called? instantaneous speedinstantaneous speed

Example-Bus ride to school this Example-Bus ride to school this morningmorning

In riding the bus this morning, the driver In riding the bus this morning, the driver has an idea of how long it will take to has an idea of how long it will take to cover a certain distance. The bus did not cover a certain distance. The bus did not travel the same speed during the whole travel the same speed during the whole trip. What is the type of speed the driver trip. What is the type of speed the driver is concerned with?is concerned with? AVERAGE SPEEDAVERAGE SPEED What is the formula for this type of speed?What is the formula for this type of speed?

average speed = total distance / total timeaverage speed = total distance / total time

s = ds = dtt/t/ttt What does the bar over the s indicate?What does the bar over the s indicate?

averageaverage

Watch your teacher:Watch your teacher: How is this type of speed different How is this type of speed different

than what you have seen so far?than what you have seen so far?covered same distance with each step

Watch the car: (battery operated Watch the car: (battery operated car)car) What would you call this type of What would you call this type of

speed?speed?constant speedconstant speedequal distances in equal amounts of timeequal distances in equal amounts of time

How does the driver of an automobile How does the driver of an automobile ensure they are traveling at this type of ensure they are traveling at this type of speed?speed? Cruise controlCruise control

What are the parts of a car that control What are the parts of a car that control speed?speed? gas pedal (accelerator)gas pedal (accelerator) brake pedal (decelerator)brake pedal (decelerator)

NO MATTER WHAT TYPE OF SPEED WE NO MATTER WHAT TYPE OF SPEED WE ARE TALKING ABOUT WE ARE STILL ARE TALKING ABOUT WE ARE STILL INTERESTED IN THE CHANGE OF INTERESTED IN THE CHANGE OF POSITION IN A GIVEN AMOUNT OF TIME.POSITION IN A GIVEN AMOUNT OF TIME.

Sample Problems:Sample Problems: 1. 1. What is the average speed of a marble What is the average speed of a marble

that rolls 45 centimeters in 5 seconds?that rolls 45 centimeters in 5 seconds? GG

d= 45cmd= 45cm t= 5st= 5s

UU s =?s =?

EEs = ds = dtt/t/ttt

SS s = 45cm / 5s = 9cm/ss = 45cm / 5s = 9cm/s

SS s = 9cm/ss = 9cm/s