Please enable JavaScript.
Coggle requires JavaScript to display documents.
Stopping Distances & Momentum - Coggle Diagram
Stopping Distances & Momentum
Stopping Distance
Definition
Distance travelled before a vehicle stops
Equation
Stopping Distance
=
Thinking Distance
+
Braking Distance
Thinking Distance
Distance travelled during reaction time
Affected By
Speed
Higher speed = greater thinking distance
Reaction Time
Tiredness
Alcohol
Drugs
Distractions
Braking Distance
Distance travelled after brakes applied
Affected By
Speed
Higher speed = greater braking distance
Road Conditions
Wet roads
Icy roads
Tyre Condition
Worn tyres
Brake Condition
Worn brakes
Faulty brakes
Braking and Friction
Brake pads press on wheels
Friction transfers energy
Kinetic Energy Store
↓
Thermal Energy Store
Higher Speed
More kinetic energy
Greater braking force needed
Greater stopping distance
Typical Stopping Distances
30 mph
23 m
50 mph
38 m
70 mph
75 m
Stopping Distance Graphs
Stopping distance increases with speed
Braking distance increases faster than thinking distance
Higher speed
Much larger braking distance
Much larger stopping distance
Leave Enough Space
Allows time to react
Allows safe stopping
Higher speed
More space needed
Reaction Time
Definition
Time taken to react to an event
Typical Values
0.2 s to 0.9 s
Affected By
Tiredness
Alcohol
Drugs
Distractions
Ruler Drop Test
Person drops ruler
Ruler caught as quickly as possible
Distance fallen measured
Longer distance
Longer reaction time
Improving Reliability
Repeat measurements
Calculate mean
Use same ruler
Same method each time
Momentum
Definition
Mass in motion
Vector quantity
Equation
Momentum = Mass × Velocity
p = mv
Units
kg m/s
Increasing Momentum
Greater mass
Greater velocity
Conservation of Momentum
Closed System
Total momentum before
=
Total momentum after
Applies To
Collisions
Explosions
Collision Example
Objects stick together
Momentum conserved
Explosion Example
Objects move apart
Momentum conserved
Changes in Momentum
Force changes momentum
Newton's Second Law
F = ma
Rate of Change of Momentum
Force = Change in Momentum ÷ Time
F = mΔv ÷ Δt
Larger Force
Faster change in momentum
Impact Forces
Large force
Short stopping time
Small force
Long stopping time
Safety Features
Purpose
Increase stopping time
Reduce force exerted
Crumple Zones
Car deforms
Increases stopping time
Seat Belts
Stretch slightly
Increases stopping time
Air Bags
Cushion impact
Increases stopping time
Other Examples
Bike helmets
Crash mats
Playground surfaces
Exam Equations
Stopping Distance
Thinking Distance + Braking Distance
Momentum
p = mv
Force
F = mΔv ÷ Δt
Exam Questions
Calculate momentum
Calculate force from change in momentum
Explain conservation of momentum
Compare thinking and braking distance
Explain factors affecting stopping distance
Explain reaction time
Explain how safety features reduce injury