Transcript 2_4 On the Road

2_4 On the Road
06 April 2016
Look at the data for the BMW 3 Series below.
What is the connection between power and acceleration?
Model
318
320
325
330
335
Acceleration
0 – 62 mph in s
9.1
8.2
6.7
6.1
5.6
Power
kW
105
125
160
200
225
Mass
kg
1435
1445
1535
1555
1610
2_4 On the Road
06 April 2016
Any similarities?
Model
318
320
325
330
335
Acceleration
0 – 62 mph in s
9.1
8.2
6.7
6.1
5.6
Power
kW
105
125
160
200
225
Power x
Accn
956
1025
1072
1220
1260
Mass
kg
1435
1445
1535
1555
1610
2_4 On the Road
06 April 2016
• What is the resultant force at constant
velocity?
• What does the stopping distance of a
vehicle depend on?
• What factors increase stopping
distance?
The “Bloodhound” supersonic
car is aiming to go faster
than 1000mph! Not even a
plane has been that fast at
sea level!
Why do cars have a top speed?
What does this table tell you about
these cars?
X3
What must happen to the forces at top
speed for there to be no acceleration?
Model
Top speed, Power,
mph
kW
X3 2.0 D
127
130
120D
142
130
320D
143
130
520D
144
130
520D Tourer 139
130
120D
320D
520D
Tourer
Forces on cars
Air resistance
Force from engine
• No resultant force means no acceleration.
• Top speed is reached when the
_________ from the ________ equals
the _________ from the air resistance.
Stopping distances
Car travelling at 1000mph
Thrust force
Drag force
What happens if the thrust force reduces?
How much distance would this need to stop at 500 m/s?
Stopping distances
Car travelling at 1000mph
Thrust force
Drag force
What happens if the thrust force reduces?
Car slows down.
How much distance would this need to stop at 500 m/s?
Around 2.5 miles!
Highway code stopping distances
• Thinking distance = distance covered before brakes
are applied.
• Braking distance = distance covered while braking.
What can increase stopping distance?
Thinking distance
Braking distance
Summary
• Thinking distance is how far a car
travels before a driver hits the brakes.
• Braking distance is how far the car
travels while braking.
• Stopping distance is thinking distance +
braking distance.