Speed

3 brothers who all act differently

Rate and Speed

• A rate can generally be described as any change of any sort over time

• Speed is a kind of specialized rate, it is the change in distance over time

• Speed = Distance /Time

• Because the unit for distance is meter and the unit for time is seconds, the unit for speed is meter per second (m/s)

(The term “per” means “divided by”)

SPEED

• PLEASE NOTE SPEED CAN’T BE NEGATIVE, IT IS ALWAYS POSITIVE

• SPEED DOES NOT HAVE A DIRECTION

• Think about, when you are traveling in reverse, does the speedometer read a negative number – NO!!

The 3 Headed-Speed Monster• There are 3 different kinds of speed

–Instantaneous Speed–Average Speed–Constant Speed

• Instantaneous Speed is how fast an object is traveling at any given moment in time, this is difficult to determine without calculus

• When a radar gun tracks your speed this is instantaneous speed

Average Speed• Average speed is equal to total distance

traveled over the total time it took to do it• Average Speed = Total Distance/Total

Time• Average speed is used for calculating

things like trip speed where there may be stops, slow downs and changes in instantaneous speed

Constant Speed

• Constant Speed is a rate that does not change

• Examples of constant speed are setting your cruise control or the hands on a clock

• Note the with constant speed, every “instant” is the same speed, so instantaneous speed is easy to determine

Set it and forget it

Speed vs. Velocity

Directionally challenged Steve has a hard time with velocity!!

Velocity• Velocity is equal to distance divided by time

– Velocity = Distance / Time• The unit for speed and velocity is m/s (meters

per second)• Velocity always has a direction, this is usually

indicated with a negative or positive sign– Positive = moving forward– Negative = moving backward

• Velocity = Speed + direction

Direction

• Any value that is expressed as a number and a direction is called a VECTOR!

• Velocity is a vector• Speed is NOT a vector

–Why?–Speed has NO DIRECTION

Velocity is a vector quantity, it has a direction!

Vectors!? Direction!?

• Problem:– A storm is 10 km away and is moving at a

speed of 60 km/h. Should you be worried?

It depends on the storm’s direction!

The Parallel Parker• A car parking in parallel is initially traveling

forward so the speed and velocity is positive• The car then stops, now the velocity and the speed is

0.• The car then shifts into reverse and travel at a speed

of 1m/s, what is its velocity?• -1m/s (note the negative sign to indicate the car is

traveling in reverse)• The car then stops again so its velocity and speed

are 0.• Finally the car pulls forward and the speed and

velocity are both positive

Vocab Movie Poster• Pick one word from

your list• On Your Poster…

– Vocab word– Graphics/Pictures/words

that help to represent your definition

– Be creative & have fun

A movie poster generates excitement and A movie poster generates excitement and desire to see the movie, do the same desire to see the movie, do the same

for your word!for your word!

Learning Target:Learning Target: I will I will compare speed and velocitycompare speed and velocity

What does it mean to go “fast”? Can that mean something different for

different people? Explain…

Share Your Poster

• Each group member will share poster– Explain your Explain your

word & Graphicsword & Graphics– Take QuestionsTake Questions