CARSSpeed and Acceleration

Speed Speed

To be able to:

All Most Some

Define what speed is..

(MYP 2/3)

Use the speed formula triangle to calculate speed

(MYP 3/4)

Analyse speed and time graphs

(MYP 5/6)

Starter – Describe how your car over comes/uses the forces acting upon it…

Use your research to help you

Criteria A C E

Put the following in order …Put the following in order …1. of speed2. in some creative way you choose

m/s100m runner 100m/10s 10.0Bicycle to school 8 mph 3.6cheetah 70 mph - a sneeze can outrun a cheetah 31.3Concorde cruising speed 2100km/h 583.3Inter-city train 125 mph 55.9Marathon runner 2hr 10min / 26 mi 385 y 5.2snail "A garden snail named Archie, owned by Carl Branhorn of Pott Row,

England, covered a 13 inch course in 2 minutes at the 1995 World Snail Racing Championships, held in Longhan, England."

0.003

sneeze 150 kmh A sneeze is a result of a sudden relaxation of the diaphragm together with the intercostal muscles that expand our lungs and abdominal muscle contraction. This results on a mass compression effect of the lungs on a short onset and causes a violent expulsion of air in the form of the sneeze

41.7

sound in air at NTP (vacuum?!) 344.0Sports car on M6 80 mph 35.8

To work out the speed of an object you need to know:

Distance, Time and SpeedDistance, Time and Speed

the distance travelled

how long it took to travel that distance.

Average speed is calculated using this equation:

Speed can be measured in different units, e.g. m/s, km/h, km/s, miles per hour.

The units of distance and time used will determine the units to be used for speed.

d

s × t

formula triangle

Calculating Average Calculating Average SpeedSpeed

total distance

total time

average speed =

Speed formula triangleSpeed formula triangle

0.5 h=

10 km

A girl takes 30 minutes to travel around a cross-country ski course, a distance of 10 km. Calculate her average speed

in km/h.

= = 2020 km/hkm/h

Speed calculation Speed calculation exampleexample

d (distance in km)average speed (in km/h) t (time in h)

=

10 km

1,800 s10,000 m

= = = 5.65.6 m/sm/s

Sometimes the units have to be changed in a speed calculation.

30 × 60

Speed calculation example – Speed calculation example – units units

Calculate the average speed of the skier in m/s.

d (distance in m)average speed (in m/s) t (time in s)

=

10 km

= 3.6 km/h x 0.5 h

distance (km) = speed (km/h) x time (h)

A boy sets off for a walk around his village at an average speed of 3.6 km/h. How far will he travel in 30 minutes?

Give your answer in km.

Distance calculationDistance calculation

= = 1.8 km1.8 km

How long would it take the boy to walk 200 m to the church, if his average speed was 1.6 m/s?

Time calculation – Question 1Time calculation – Question 1

200 m

1.6 m/s =

time =distance

speed

= 125= 125 secondsseconds

Car graphing activity – animationCar graphing activity – animation

Distance–time graphDistance–time graph

Calculating speed from the Calculating speed from the gradientgradient

The slope of a graph is called the gradient.

The gradient of the line in adistance–time graph equals the speed.

It is difficult to calculate the gradient of ‘realistic’ graphs because the line is curved.

Simple graphs use straight lines only, making it easy to calculate the gradient.

time

dis

tan

ce

time

dis

tan

ce

What is the speed of the object between points A and B?

time (s)

dis

tan

ce (

m)

0 21 3 4 5 6 7 8 90

10

20

30

40

50

60

70

A

B the object has moved

60 m (70 - 10 )

it took 3 s to move this distance (6 - 3)

speed = distance/time

= 60/3

= 20= 20 m/sm/s

What’s the speed?What’s the speed?

1. Time how long it takes you to run 100 m.

Speed experiment – instructionsSpeed experiment – instructions

total distance

total time

average speed =

3. Repeat the experiment for each member of your group.

2. Then calculate your average speed for the run.

4. What was the fastest average speed for your group?

Name distance (m) time (s) average speed (m/s)

Conclusion

The fastest member of the group, with an average speed of ___________, was _____________.

Speed experiment – results Speed experiment – results

100100

100100

100100

100100

100100

Speeding up vs slowing downSpeeding up vs slowing down

HomeworkHomework

What is the top speed of your car? What is the top speed of your car? What features does it have to What features does it have to enable it to have this speed? enable it to have this speed?

Add to your Scrap book.Add to your Scrap book.

Speed Speed

To be able to:

All Most Some

Define what speed is..

(MYP 2/3)

Use the speed formula triangle to calculate speed

(MYP 3/4)

Analyse speed and time graphs

(MYP 5/6)

Starter – Describe how your car over comes/uses the forces acting upon it…

Use your research to help you

Criteria A C E

Acceleration Acceleration To be able to:

All Most Some

Explain what acceleration is.

(MYP 2/3)

Use the formula triangle to solve acceleration problems.

(MYP 3/4)

Think about how your cars is designed to improve its acceleration.

(MYP 5/6)

Criteria A C E

The acceleration is the rate in which an object slows down or speeds up.

A train accelerates in a straight line from rest. As it does, its velocity

increases.

The brakes on this motorcycle are causing it to slow down.

This is negative acceleration or deceleration.

What is acceleration?What is acceleration?

The acceleration of an object can be calculated using this equation:

change in speed time taken

acceleration =

Acceleration is measured in metres per second per second (m/s2).

Change in speed is measured in metres per second (m/s).

Time taken is measured in seconds (s).

How is acceleration calculated?How is acceleration calculated?

Using a formula triangleUsing a formula triangleA formula triangle helps you to rearrange a formula. The

formula triangle for acceleration (a), speed (s) and time (t) is shown below.

x

Cover the quantity that you are trying to work out, which gives the rearranged formula needed for the calculation.

So to find acceleration (a), cover up a…

…which gives the formula…

a =a =ss

tt

A racing car accelerates from rest to a speed of 60 m/s in a time of 4 seconds. What is the acceleration of the car?

= = 1515 m/sm/s22

change in speed

time takenacceleration =

= 60

4

Acceleration problemAcceleration problem

A hungry cheetah spots a gazelle and decides to chase it. The cheetah accelerates at 10 m/s2 from rest until it reaches

20 m/s. How long did this take?

acceleration = change in speedtime taken

= 2010

= = 22 ss

Acceleration problemAcceleration problem

time taken = change in speed

acceleration

Acceleration problems calculationsAcceleration problems calculations

HomeworkHomework

Acceleration of your car? Acceleration of your car? How fast can it go 0-60?How fast can it go 0-60?

0-100? 0-100?

Add to your Scrap book.Add to your Scrap book.

Acceleration Acceleration To be able to:

All Most Some

Explain what acceleration is.

(MYP 2/3)

Use the formula triangle to solve acceleration problems.

(MYP 3/4)

Think about how your cars is designed to improve its acceleration.

(MYP 5/6)

Criteria A C E

Reaction Times Reaction Times To be able to:

All Most Some

Understand what reaction time is.

(MYP 2/3)

Explain what can affect reaction time.

(MYP 3/4)

Discuss the social and economical implications of speed limits.

(MYP 5/6)

Criteria A C E

Reaction TimeReaction TimeThe time it takes you to respond to a stimulus.

e.g. time between seeing a red light and applying the brakes.

Under test condition, reaction time is approximately 0.75 s

In real conditions it’s about 1 s

Reaction DistanceReaction Distance

The distance the car travels in this time.

Stopping Distances Stopping Distances

To be able to:

All Most Some

Understand what stopping and thinking distances are

(MYP 2/3)

Explain what can affect stopping and thinking distances

(MYP 3/4)

Discuss the social and economical implications of speed limits

(MYP 5/6)

Starter – Why do we have speeding limits

Criteria A C E

Speed and SafetySpeed and SafetyWhy are speed limits important?

Why have speed limits?Why have speed limits?Speed limits are an important part of road safety. They aim to prevent drivers from driving at speeds that are unsuitable

and unsafe.

The speed limit of a particularroad depends on a range offactors, such as how straight or curved it is, and its location.

The faster a vehicle is driving, the longer it will take to stop – the overall distance this takes is the stopping distance.

stopping distance = thinking distance + braking distance

Thinking distance is the distance a car travels before the brakes are applied.

Braking distance is the distance a car travels whilst the brakes are being applied.

Stopping distance = thinking distance + braking distance

Stopping distance

Braking distance

Thinking distance

How long does it take a moving vehicle to stop?

The stopping distance is the sum of the thinking distance and the braking distance.

Stopping DistanceStopping Distance

Can you match up the words with their Can you match up the words with their definitions?definitions?

Stopping distance

Friction

Thinking distance

Braking distance

One of the forces the road exerts on the tyres as the car is stopping.

The distance a car travels whilst it is braking.

The distance a car travels before the brakes are applied.

The sum of thinking distance and the braking distance.

What factors affect braking and thinking What factors affect braking and thinking distance?distance?

Thinking distanceThinking distance Braking distanceBraking distance

Speed of car

Speed of car Speed of car

Road conditions

Road conditions

Drugs and alcohol

Drugs and alcohol

Tiredness

Tiredness

Medication

Medication

Condition of tyres

Condition of tyres

Condition of brakes

Condition of brakes

Braking Car Question:Braking Car Question: A car is moving along an open road. Suddenly, a A car is moving along an open road. Suddenly, a

sheep walks into the road.sheep walks into the road.

a) What do we call the distance the car travels before the driver puts their foot on the brakes?

b) Name one factor that could increase the distance the car travels in this time.

c) The braking distance is 35m for the car. If the stopping distance is 50m, how far did the car travel before the driver put their foot on the brakes?

Thinking distance

Medication, drugs/alcohol, speed of car, tiredness

Thinking distance = Stopping distance – braking distance

= 50m – 35m

= 15m

This graphing experiment shows a movie of a car travelling along a straight road.

Copy the results table shown on the next slide and complete it as the movie is playing.

Record the distance the car has travelled every five seconds.

Then graph your results.

Note that there are teacher’s notes, in “Notes View” on this slide.

Car Graphing ActivityCar Graphing ActivitySee teacher’s notes

Results table for Results table for Distance / Time Distance / Time

GraphGraph

Time (s)Time (s) Distance (m)Distance (m)00

55

1010

1515

2020

2525

3030

3535

4040

4545

5050

5555

Results table for Results table for Distance / Time Distance / Time

GraphGraph

Time (s)Time (s) Distance (m)Distance (m)0

5

10

15

20

25

30

35

40

45

50

55

0

904

76

186

234

484

634

784

994

974

16

994

Stopping DistancesStopping Distances

Stopping Distances Stopping Distances

To be able to:

All Most Some

Understand what stopping and thinking distances are

(MYP 2/3)

Explain what can affect stopping and thinking distances

(MYP 3/4)

Discuss the social and economical implications of speed limits

(MYP 5/6)

Criteria A C E

alcohol

other drugs and some medicines

tirednessdistractions, such asmobile phones

speed

What affects thinking What affects thinking distance?distance?

The thinking distance is the distance a vehicle travels in the time it takes for a driver to react to a situation and apply the

brakes.

What factors will affect thinking distance?

weather

condition of tyres/brakes

What affects braking What affects braking distance?distance?The braking distance is the distance a vehicle takes to stop

once the driver has applied the brakes.

What factors will affect braking distance?

condition of road

speed

Factors affecting stopping Factors affecting stopping distancesdistances

How do speed cameras How do speed cameras work?work?

There are several types of speed camera., They use different methods to calculate the speed of a vehicle.

Gatso speed cameras use radar to detect the speed of a vehicle, then take two photos (half a second apart) to

provide visual evidence. Lines marked on the road indicate how far the vehicle has travelled in that time.

Truvelo speed cameras are activated by pressure detector cables in the road. The cables are 10 cm apart and a computer calculates how long it

takes the vehicle to pass from one to another, and therefore the speed of the vehicle.

Speeding and speed Speeding and speed camerascameras

Stopping a car…Stopping a car…

Braking distance

Too much alcohol

Thinking distance

Tiredness

Too many drugs

Wet roads

Driving too fast

Tyres/brakes worn out

Icy roads

Poor visibility

Stopping Distances Stopping Distances To be able to:

All Most Some

Understand what stopping and thinking distances are

(MYP 2/3)

Explain what can affect stopping and thinking distances

(MYP 3/4)

Discuss the social and economical implications of speed limits

(MYP 5/6)

Criteria A C E

ReviewReview