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P3 Spaced learning
Forces for transport
Speed = Average Distance/Time
KM x 1000 = M
M / 1000 = KM
• increasing the speed, increases the
distance travelled in the same time
• increasing the speed, reduces the
time to cover the same distance.
distance = average speed × time
=(u + v)/2 × t
d is the distance
u is the starting speed
v is the finishing speed
t is the time taken
Average
Speed Cameras
Takes two photos, a certain time apart,
when the vehicle moves over marked lines
a know distance apart.
Use the
unit s on
the graph
combined
for speed
Speed
Graphs – distance / time graphs, how
the distance changes over time.
Gradient (steepness) = speed (steeper
faster)
Steady speed – straight diagonal line
(up or down)
Stationary – horizontal line
You need to be able to draw one.
Non – uniform speed:
Curved line upwards – acceleration
Curved line downwards - decceleration
Changing speed
Velocity – speed and direction
Objects moving in opposite
acceleration = change in speed / time taken
directions at the same
A change in speed per unit of time
speed, velocities have
Change in speed = end speed – start speed
identical magnitude but
opposite signs. E.g. +30m/s
- metres per second squared (m/s2)
- involves change in speed and/or direction
and – 30m/s
Relative velocity:
Velocity A – Velocity B e.g.
+30 m/s - +20 m/s =+10 m/s
OR
+30 m/s - -20 m/s =+50 m/s
Horizontal line - constant speed
Straight line (positive gradient) - constant positive acceleration (speeding up)
Straight line (negative gradient) - constant negative acceleration e.g. -2m/s (slowing
down) or deceleration
Steeper line (greater change in speed in given time)– higher acceleration
Curved line –up increasing acceleration –down decreasing acceleration
Gradient = acceleration
You need to be able to draw one
Calculate distance – area
under the graph (meters)
Force - newtons, N
Mass - kilograms, kg
Acceleration -metres per second
squared, m/s2
force = mass × acceleration
Speed and:
thinking distance – increases linearly
braking distance – increases as a
squared relationship e.g. x2 x4, x3 x9.
Thinking distance - the distance travelled between the need for braking occurring and the brakes
starting to act. Increased if: Tired, Distracted or not concentrating, Under the influence of alcohol or other
drugs, increased speed, distractions or lack of concentration.
Braking distance - the distance taken to stop once the brakes have been applied. Increased if: The
car's brakes or tyres are in poor condition, The road and weather conditions are poor (icy or wet roads, for
example)., increased speed, Friction, mass, speed, braking force.
Stopping distance - thinking distance + braking distance.
stopping distance = thinking distance + braking distance
Forces and motion
Resultant force is zero - stay at the same
speed.
Resultant force is not zero - speed up or slow
down, +ve or –ve.
Speed up - resultant force is in the same
direction as object is moving
Slow down - resultant force is in the opposite
direction
Road safety - Speed limits go no faster than safe for
normal conditions.
Road conditions- icy etc.
‘tail gates’ –drives too close
to the vehicle in front,
(inside thinking distance).
Work and Power
weight = mass × gravitational field strength
Weight -newtons, N
Mass -kilograms, kg
The gravitational field strength -newtons per kilogram, N/kg
Mass - how much stuff is in an object.
Weight - force acting on that stuff due to gravity.
gravitational field strength of the Moon is
about one-sixth of that of the Earth
Power -watts, W
Work done -joules, J
Time -seconds, s
Use and understand the
derivation of the power
equation in the form:
power = force × speed
Power = Work done / time
How quickly work is being done. Watts (W).
Cars:
• have different power ratings
• have different engine sizes
Affecting fuel consumption – environmental issues, cost
Work done = force × distance
Work done -joules, J
Force - newtons, N
Distance - metres, m
J also used for energy
Examples
• lifting weights
• climbing stairs
• pulling a sledge
• pushing a shopping trolley.
Depends on:
the size of the force in
newtons (N)
the distance travelled in
metres (m).
Energy on the move
(derivatives of) fossil fuels - fuels in road
transport: petrol, diesel. Will run out
Carbon dioxide - greenhouse gas (global
warming) Sulfur dioxide - cause of acid rain.
Alternatives - bio-fuels and solar energy.
• reduce pollution at the point of use
• produce pollution in their production
• may lead to an overall reduction in CO2
emissions.
Electricity used for road transport, battery
driven cars, solar power/cars with solar panels,
do not pollute at point of use.
Recognise that battery driven cars need to
have the battery recharged:
• this uses electricity from a power station
• cause pollution
Kinetic energy – depends on mass and speed
KE = ½ mv2
or
KE = ½ × m × v2
KE = the kinetic energy in joules, J
m = the mass in kilograms, kg
v = the speed in metres per second, m/s
kinetic energy proportional to speed squared,
braking distances proportional to the speed
squared. Rearrange equation for kinetic
energy. m = (2 × KE) ÷ v2
v2 = (2 × KE) ÷ m
Affect on fuel consumption:
Shape - wedge shape of sports car, deflectors on
lorries and caravans, roof boxes on cars, driving
with car windows open.
Other factors - Driven uphill a lot, Carrying large
loads or not, Driven at high speed, Driven over
rough road surfaces, Driven with underinflated
tyres. energy required to increase KE, energy
required to do work against friction, driving
styles and speeds, road conditions.
Crumple zones
Momentum = mass × velocity
Momentum - kilograms metres per
second, kg m/s
Mass - kilograms, kg
Velocity - metres per second, m/s
Force = change in momentum ÷ time
Force - newtons, N
Change in momentum - kilograms metres per
second, kg m/s
Time - seconds, s
Sudden change in momentum – large
force- cause injury
Change in momentum - the longer the time
taken, the smaller the force needed.
Car safety features
Risks and benifits
Falling safely
The energy of games and theme rides
Musical Chairs
Speed = Average Distance/Time
KM x 1000 = M
M / 1000 = KM
• increasing the speed, increases the
distance travelled in the same time
• increasing the speed, reduces the
time to cover the same distance.
distance = average speed × time
=(u + v)/2 × t
d is the distance
u is the starting speed
v is the finishing speed
t is the time taken
Average
Speed Cameras
Takes two photos, a certain time apart,
when the vehicle moves over marked lines
a know distance apart.
Use the
unit s on
the graph
combined
for speed
Speed
Graphs – distance / time graphs, how
the distance changes over time.
Gradient (steepness) = speed (steeper
faster)
Steady speed – straight diagonal line
(up or down)
Stationary – horizontal line
You need to be able to draw one.
Non – uniform speed:
Curved line upwards – acceleration
Curved line downwards - decceleration
Changing speed
Velocity – speed and direction
Objects moving in opposite
acceleration = change in speed / time taken
directions at the same
A change in speed per unit of time
speed, velocities have
Change in speed = end speed – start speed
identical magnitude but
opposite signs. E.g. +30m/s
- metres per second squared (m/s2)
- involves change in speed and/or direction
and – 30m/s
Relative velocity:
Velocity A – Velocity B e.g.
+30 m/s - +20 m/s =+10 m/s
OR
+30 m/s - -20 m/s =+50 m/s
Horizontal line - constant speed
Straight line (positive gradient) - constant positive acceleration (speeding up)
Straight line (negative gradient) - constant negative acceleration e.g. -2m/s (slowing
down) or deceleration
Steeper line (greater change in speed in given time)– higher acceleration
Curved line –up increasing acceleration –down decreasing acceleration
Gradient = acceleration
You need to be able to draw one
Calculate distance – area
under the graph (meters)
Force - newtons, N
Mass - kilograms, kg
Acceleration -metres per second
squared, m/s2
force = mass × acceleration
Speed and:
thinking distance – increases linearly
braking distance – increases as a
squared relationship e.g. x2 x4, x3 x9.
Thinking distance - the distance travelled between the need for braking occurring and the brakes
starting to act. Increased if: Tired, Distracted or not concentrating, Under the influence of alcohol or other
drugs, increased speed, distractions or lack of concentration.
Braking distance - the distance taken to stop once the brakes have been applied. Increased if: The
car's brakes or tyres are in poor condition, The road and weather conditions are poor (icy or wet roads, for
example)., increased speed, Friction, mass, speed, braking force.
Stopping distance - thinking distance + braking distance.
stopping distance = thinking distance + braking distance
Forces and motion
Resultant force is zero - stay at the same
speed.
Resultant force is not zero - speed up or slow
down, +ve or –ve.
Speed up - resultant force is in the same
direction as object is moving
Slow down - resultant force is in the opposite
direction
Road safety - Speed limits go no faster than safe for
normal conditions.
Road conditions- icy etc.
‘tail gates’ –drives too close
to the vehicle in front,
(inside thinking distance).
Work and Power
weight = mass × gravitational field strength
Weight -newtons, N
Mass -kilograms, kg
The gravitational field strength -newtons per kilogram, N/kg
Mass - how much stuff is in an object.
Weight - force acting on that stuff due to gravity.
gravitational field strength of the Moon is
about one-sixth of that of the Earth
Power -watts, W
Work done -joules, J
Time -seconds, s
Use and understand the
derivation of the power
equation in the form:
power = force × speed
Power = Work done / time
How quickly work is being done. Watts (W).
Cars:
• have different power ratings
• have different engine sizes
Affecting fuel consumption – environmental issues, cost
Work done = force × distance
Work done -joules, J
Force - newtons, N
Distance - metres, m
J also used for energy
Examples
• lifting weights
• climbing stairs
• pulling a sledge
• pushing a shopping trolley.
Depends on:
the size of the force in
newtons (N)
the distance travelled in
metres (m).
Exam questions