Download Week 3 Routine and Defensive_Natural Law

Physics, Mechanics and
Maintenance
“Who let the apple fall out of the
tree?”
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Physics
• Natural Laws you can’t change
• Measurable and predictable
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Friction
Inertia
Gravity
Kinetic energy
Force of impact
Skid control and Stopping distance
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What happens when you break
the laws of nature?
• The best of intentions cannot change the
laws of nature.
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Friction
• Resistance to motion
• Necessary to control vehicle
• Control of vehicle depends on friction to
tire on the surface of the road.
– AKA….traction
• Must know condition of road
– Effect on your tires
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Influences on Traction
• Wet, snow, ice, mud, loose gravel
– Condition of road surface
• Bumpy road
– Reduced friction thus control
• Hydroplaning
– Water between tires and road surface
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Hydroplaning
• Factors that influence
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Standing water
Depth of tread on tires
Design of tire tread
Speed of vehicle
Demands of vehicle
• Corners
• Hills
• Braking
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What is the surface made of?
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Dirt
Gravel
Asphalt
Cement
Brick
Misc.
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Dirt
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Dusty
Soft
Moisture effect
Rough
Limit speed
Not usually mapped
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Gravel
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Rough, can be washboard
Hard to steer
Hard on tires
Limit speed and traction
Potholes
Rock chips
Dusty
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Asphalt
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Most common
Usually smooth
Sloped for drainage
Good traction
Speed limited by other factors
Slick in adverse weather (snow, ice, rain)
Oil leeches out
Potholes are sharp edged
Rutted
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Cement
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Smooth with expansion joints
Good traction
Sloped for drainage
Speed limited by other factors
Slick in adverse weather
Different slab heights
Less pliable
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Brick
• Mostly decorative
• Less friction
• Rough ride
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Other Misc
• Metal
• Wood
• Mixture
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Bridges
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May be narrow
No shoulder
Freeze first
Metal are very
slippery, especially
when wet or oily
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Tire influence on traction
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Tread Wear
Tread pattern
Studs, siped
Tire pressure
Chains
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Inertia
• An object in motion tends to
stay in motion unless acted
upon by a force applied to
change its rate or direction.
• Traction is your way to
overcome inertia
– Not enough traction and you
crash
• Stopping
• Turning
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Corners
• Centrifugal force wants to go straight
• Traction needed to turn
– Reduced traction, reduce speed
– Snow, ice, etc.
• Banking for improved speed turn
– Lean into curve
– Reverse banking makes high hazard
• Guard rails present?
• What is your visibility around corner
– Can you stop in time?
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How fast to go around corner?
• Use good judgment to judge
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Curve radius
Bank
Surface
Condition
Speed
Visibility
Traffic volume
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Curve Radius
• Low speed curves (<40 mph)
– Constant curve
– With or without banking
• High Speed Curves (>40 mph)
– Gradual onset
– Increasing curve
– Gradual return to straight
– Banking
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Curve Radius (cont.)
• Combinations are Dangerous
– Require changes in speed and adjusted steering
– Heavy braking causes vehicle spin
• Posted speeds
– Recommended to be comfortable
– 15mph over usually OK
– Not if <25mph
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Let’s talk about Visibility!
• How far can you see?
– Are you overdriving your visibility?
– Stopping distance for conditions present
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Corners
Hills
Buildings
Vehicles (Trucks in particular)
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Gravity
• “Why did the apple fall?”
• Weight of vehicle is a big factor
– Acceleration and braking
• Uphill and Downhill
– Changes vehicle actions
• Change of weight distribution
– Center of gravity
– More on front or rear tires
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Kinetic Energy
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AKA momentum
At rest……….stored energy
In motion……….kinetic energy
K=1/2 mass X velocity squared
(KE=½ MV2)
• What is the most important factor?
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Let’s look at some examples:
• You are driving your ambulance 20 mph
• Now you accelerate to 40 mph
– How much more kinetic energy?
– 4 times the energy
• Now accelerate to 80 mph
– Now how much more kinetic energy
– 16 times more
– 16 times more potential for damage
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Force of Impact
• Influenced by
– Speed*****
– Weight
– Suddenness of stop
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Force of Impact
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What are you hitting?
Is it going to give any?
Is it adding KE to the equation
Who is bigger, moving faster?
Mechanical Engineering
– Vehicles are made to absorb energy
– Energy absorbed in vehicle is not in patient or
you!
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Skid Control
• Loss of traction=skid
• What do you do if you skid?
– Stop braking
– Turn into direction of skid
• Usually the back end of vehicle
– Be prepared for secondary skids
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Skid Prevention
• Causes of skids
– Over-accelerating
• Ease up on gas pedal
– Over-steering
• Inertia greater than traction
• Slow down and turn slower
– Over-braking
• Breaks lock up
• Release brakes
– Re-establish traction
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Stopping Distance
• “48 vehicle pile-up on I-80 due
to fog”
• Common problem on freeways
• Stopping Distance Factors:
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Perceive potential hazard
Identify unsafe situation
Make decision to stop
React by pressure on brake pedal
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Breaking Distance?
• Reaction time
– Mental alertness
– Anticipation
– Foot on brake before
• Brakes applied
• Friction stops vehicle
– Most variables
– Tires, Road surface,
etc.
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Examples tell the story
• At 55 mph
– Perception+reaction+braking=228feet
• At 65 mph
– Perception+reaction+braking=305feet
• That’s 100 yards!
• Many things can influence the braking
distance………….
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Influences to Stopping Distance
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Vehicle Speed
Perception time#
Reaction time#
#driver condition
Weather
Road conditions
Weight of Ambulance
Condition of tires *
Brake condition *
*Preventative Maint.
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Influences to Stopping Distance
• Brake ability
– Heat
– Dust
– Water
• Brake fade
– 700o liner – shoes melt
– Disc better than drum
– Less surface friction
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Type I Ambulance
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Type I Ambulances
Truck chassis with mounted
patient care box
· Box and cab are separated
· No walk through area
between patient compartment
and drivers compartment
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Type II Ambulance/Rescue
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Type II Ambulances
Van body
· Raised roof
· Walk area between cab
and patient compartment
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Type III Ambulance/Rescue
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Type III Ambulances
Patient care box
mounted on Van Chassis
· Walk through between
cab and patient care
compartment
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Following Distance
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Distance needed to stop in time!
Less traction=greater distance
Less visibility=greater distance
Heavier vehicle=greater stopping distance
Two easy rules (under ideal conditions)
– 4 second rule…
• Time to reach spot where lead vehicle is
– Car length rule
• 1 car length for each 10 mph
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Clues to help judgments
• Look for oil discoloration on road
– Usually means dip in road
• Scrapes on guardrails
– Wrecks, vehicle contact
• Shade on road
– Slick in frost conditions
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Read the Signs
• Highway Department Signs
• Use as guide to speed
• Pay attention to them!
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Loose gravel
Congestion Ahead
Slippery when wet
Safety Corridor
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A new line of work
• Painted surfaces are helpful
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Fog lines
No Passing lines (and lanes)
Solid lines versus intermittent
Merging lanes and Arrows
Reflectors
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Let’s talk just briefly on
Maintenance
• Brakes
• Tires
• Visibility (windows)
– Washer fluid
– Wiper blades
• Sirens and horns
• Panel lights
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What about the driver
• Effect on Perception and Reaction time
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Fatigue
Excitement
Illness
Medications
Pre-occupation/distraction
• Thinking about the call
– Horseplay
– Experience
• Know road and vehicle better
– Complacency********
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How to make the best out of a
bad situation!
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