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P2.1.3 Forces and braking
P2 Physics
Mr D Powell
Connection
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•
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Connect your learning to the
content of the lesson
Share the process by which the
learning will actually take place
Explore the outcomes of the
learning, emphasising why this will
be beneficial for the learner
Demonstration
• Use formative feedback – Assessment for
Learning
• Vary the groupings within the classroom
for the purpose of learning – individual;
pair; group/team; friendship; teacher
selected; single sex; mixed sex
• Offer different ways for the students to
demonstrate their understanding
• Allow the students to “show off” their
learning
Activation
Consolidation
• Construct problem-solving
challenges for the students
• Use a multi-sensory approach – VAK
• Promote a language of learning to
enable the students to talk about
their progress or obstacles to it
• Learning as an active process, so the
students aren’t passive receptors
• Structure active reflection on the lesson
content and the process of learning
• Seek transfer between “subjects”
• Review the learning from this lesson and
preview the learning for the next
• Promote ways in which the students will
remember
• A “news broadcast” approach to learning
Mr Powell 2012
Index
P2.1.3 Forces and braking
a) When a vehicle travels at a steady speed the resistive forces balance the driving force.
b) The greater the speed of a vehicle the greater the braking force needed to stop it in a
certain distance.
c) The stopping distance of a vehicle is the sum of the distance the vehicle travels during
the driver’s reaction time (thinking distance) and the distance it travels under the
braking force (braking distance).
e) When the brakes of a vehicle are applied, work done by the friction force between the
brakes and the wheel reduces the kinetic energy of the vehicle and the temperature of
the brakes increase.
f) A vehicle’s braking distance can be affected by adverse road and weather conditions
and poor condition of the vehicle.
d) A driver’s reaction time can be affected by tiredness, drugs and alcohol.
Mr Powell 2012
Index
a) When a vehicle travels at a steady speed the resistive forces
balance the driving force.
For any car travelling at constant velocity, the resultant force
on it is zero.
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This is because the motive force of its engine is balanced by
the resistive forces (i.e. friction and air resistance) on it.
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A car driver uses the accelerator pedal (also called the gas
pedal) to vary the
motive force of the engine.
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The resistive forces change to meet to the rise or fall.
Mr Powell 2012
Index
b) The greater the speed of a vehicle the greater the braking
force needed to stop it in a certain distance.
The braking force needed to stop a vehicle in a certain distance
depends on:
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the velocity of the vehicle when the brakes are first applied
the mass of the vehicle.
We can see this using the equation F = ma in which the braking force is
the resultant force.
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The greater the velocity, the greater the deceleration needed to
stop it in a certain distance. So the braking force must be greater
than at low velocity.
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The greater the mass, the greater the braking force needed for a
given deceleration.
Mr Powell 2012
Index
c) The stopping distance of a vehicle is the sum of the distance
the vehicle travels during the driver’s reaction time (thinking
distance) and the distance it travels under the braking force
(braking distance).
Travel this whilst thinking
about applying the
brakes
Now this when you
actually have your foot
on the brakes
Mr Powell 2012
Index
d) A driver’s reaction time can be affected by tiredness, drugs
and alcohol.
f) A vehicle’s braking distance can be affected by adverse road
and weather conditions and poor condition of the vehicle.
Poorly maintained vehicles, for
example with worn brakes or
tyres, take longer to stop because
the brakes and tyres are less
effective.
The faster a vehicle is
travelling, the further it
travels before it stops. This
is because the thinking
distance and the braking
distance both increase with
increased speed.
Tiredness, alcohol and drugs all
increase reaction times. So they
increase the thinking distance
(because thinking distance =
speed x reaction time).
Therefore, the stopping distance
is greater.
In adverse road conditions,
for example on wet or icy
roads, drivers have to brake
with less force to avoid
skidding. Stopping distances
are therefore greater in poor
road conditions.
Mr Powell 2012
Index
e) When the brakes of a vehicle are applied, work done by the
friction force between the brakes and the wheel reduces the
kinetic energy of the vehicle and the temperature of the brakes
increase.
Kinetic Energy = ½ mv2
As you slow the KE is
transferred into
thermal by friction
between the discs
and pads
Mr Powell 2012
Index
Summary Questions...
Mr Powell 2012
Index
Consolidate – How can you explain these things...
P2.1.3 Forces and braking Part I
a) When a vehicle travels at a steady speed the resistive
forces balance the driving force.
b) The greater the speed of a vehicle the greater the
braking force needed to stop it in a certain distance.
c) The stopping distance of a vehicle is the sum of the
distance the vehicle travels during the driver’s reaction
time (thinking distance) and the distance it travels under
the braking force (braking distance).
Consolidate – How can you explain these things...
P2.1.3 Forces and braking Part II
e) When the brakes of a vehicle are applied, work done by
the friction force between the brakes and the wheel
reduces the kinetic energy of the vehicle and the
temperature of the brakes increase.
f) A vehicle’s braking distance can be affected by adverse
road and weather conditions and poor condition of the
vehicle.
d) A driver’s reaction time can be affected by tiredness,
drugs and alcohol.