Average vs Instantaneous Speed

Slide 16 / 159

It might take 3 hours to travel 300 km in a car. What would the
average speed of the car be? Calculate it now.

Does that mean the car was going
that speed for the whole 3 hours
of the trip?

When you go on a trip in the car,
do you go the same speed the
whole time? Talk to a partner
about this.

Average vs Instantaneous Speed

s = d / ts = 300 / 3 s = 100 km/hr

no, it's just an average

Slide 17 / 159

Average vs Instantaneous Speed

Have you ever run a mile? Do you think you ran at the exact same
speed the entire mile?

Think about
what runners
do at the
very end of a
race.

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Average vs Instantaneous Speed

When you ride on the bus
to school, does the bus
driver travel at the same
speed the entire trip?

School buses and other
vehicles have
speedometers that
measure the speed of the
vehicle at a specific
moment in time.

Do speedometers measure average speed or instantaneous speed?

Since a car's speed can change at any second, the speedometer measures

instantaneous speed. They can travel 25 mph one moment and be at 0 mph
stopped at a red light the next. It does not record overall speed of the whole trip.

Slide 19 / 159

3 Your teacher times your mile run at 7.5 minutes,
that means your speed was 0.13 mile/min. Was this
your average speed or your instantaneous speed?

AAverage
Speed

BInstantaneous
Speed

*You ran an average of 0.13 mi/min,

you could've ran faster one lap and
slower the next, etc. Whenever someone
records the entire trip it's most often

average speed.

Slide 20 / 159

4 A student has built a model car that is designed to
run at a constant speed. What should the student
measure to test whether the car runs at a constant
speed, average or instantaneous speed?

A Average Speed

B Instantaneous Speed

*If the car truly travels at a

constant speed, then its speed

every single second should be
the exact same. The best way
to test this is to measure its
instantaneous speed every

second and if it stays the same
then we know it worked.

Slide 21 / 159

5 A swordfish travels for two hours. The first
hour he covers 110 kilometers, and the
second hour he covers 84 kilometers. What
is the average speed of the swordfish?

A

110 km/h

B

84 km/h

C

97 km/h

D

194 km/h

Hint: Remember that
Average speed is total
distance travelled divided
by total time

*speed is distance divided by time so we must add
the distances together first before we can solve this

110 + 84 = total distance of 194 km

s = d / ts = 194 / 2s = 97 km/h

Slide 22 / 159

6 A dog walks outside to go the bathroom every day.
On a given day, she walks 75 meters before she finds
a spot to use the bathroom. She walks at an average
speed of 2.5 meters per second. How long does it take
her to find a place to use the bathroom?

A

30 seconds

B

2 minutes

C

188 seconds

D

90 seconds

*solve for time

t = d / st = 75 / 2.5t = 30 s

Slide 23 / 159

Velocity

Velocity is another way to measure motion. Simply put, velocity

is the speed of an object with a direction included.

Runner's speed: 10 km/hr
Runner's velocity: 10 km/hr to the East

What do you notice about the units for speed and velocity?

*the units are the same, since velocity is speed we should be using

the speed units, just add a direction after

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Why is velocity important?

Have you ever been in an airplane? Would would be the consequence of

a pilot only knowing the speed of other nearby planes?

Tornadoes travel at about 170 km/h.
Why is knowing the velocity of a
tornado important?

Overall, knowing velocity is so important
because if we only knew the speed of tornadoes
or storms, etc., we wouldn't know the direction
it is going to hit in order to warn people to get
to safety.

Also, planes wouldn't know the direction of other planes and could crash.
This is also helpful in sports...for example, football kickers or golfers need to know the velocity of

the wind so they know which direction the need to hit the ball in order to make up for the wind.

Slide 25 / 159

7 Carlos and Gina are riding on their horses to go
into town. They travel 70 meters in 7 seconds going
west. What is their velocity?

A

490 m/s west

B

10 m/s west

C

490 m/s

D

10 m/s

*remember velocity is SPEED with a direction,
so anytime I ask you to solve for velocity, you
should use the SPEED formula!!

s = d / ts = 70 / 7s = 10 m/s

*now to make it velocity, add a direction!

Slide 26 / 159

8 A car travels 100 km/h west for 2 hours. The car
then travels 50 km/h east for one hour. What is the
car's final position relative to its starting position?

A

50 km west

B

150 km west

C

250 km west

D

50 km east

Hint: Find the distance
and direction traveled for
each leg of the trip first.
Draw these distances on
a number line using 0km
as the starting point.

*blue is the start, purple is the end, so they end 150 km west

*this is a challenge question - I won't put number lines on any quiz/test