Transcript Week 3 Routine and Defensive_Natural Law

Physics, Mechanics and
Maintenance
“Who let the apple fall out of the
tree?”
1
Physics
• Natural Laws you can’t change
• Measurable and predictable
–
–
–
–
–
–
Friction
Inertia
Gravity
Kinetic energy
Force of impact
Skid control and Stopping distance
2
What happens when you break
the laws of nature?
• The best of intentions cannot change the
laws of nature.
3
4
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
5
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
6
Hydroplaning
• Factors that influence
–
–
–
–
–
Standing water
Depth of tread on tires
Design of tire tread
Speed of vehicle
Demands of vehicle
• Corners
• Hills
• Braking
7
What is the surface made of?
•
•
•
•
•
•
Dirt
Gravel
Asphalt
Cement
Brick
Misc.
8
Dirt
•
•
•
•
•
•
Dusty
Soft
Moisture effect
Rough
Limit speed
Not usually mapped
9
Gravel
•
•
•
•
•
•
•
Rough, can be washboard
Hard to steer
Hard on tires
Limit speed and traction
Potholes
Rock chips
Dusty
10
Asphalt
•
•
•
•
•
•
•
•
•
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
11
Cement
•
•
•
•
•
•
•
Smooth with expansion joints
Good traction
Sloped for drainage
Speed limited by other factors
Slick in adverse weather
Different slab heights
Less pliable
12
Brick
• Mostly decorative
• Less friction
• Rough ride
13
Other Misc
• Metal
• Wood
• Mixture
14
Bridges
•
•
•
•
May be narrow
No shoulder
Freeze first
Metal are very
slippery, especially
when wet or oily
15
Tire influence on traction
•
•
•
•
•
Tread Wear
Tread pattern
Studs, siped
Tire pressure
Chains
16
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
17
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?
18
How fast to go around corner?
• Use good judgment to judge
–
–
–
–
–
–
–
Curve radius
Bank
Surface
Condition
Speed
Visibility
Traffic volume
19
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
20
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
21
Let’s talk about Visibility!
• How far can you see?
– Are you overdriving your visibility?
– Stopping distance for conditions present
•
•
•
•
Corners
Hills
Buildings
Vehicles (Trucks in particular)
22
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
23
Kinetic Energy
•
•
•
•
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?
24
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
25
Force of Impact
• Influenced by
– Speed*****
– Weight
– Suddenness of stop
26
Force of Impact
•
•
•
•
•
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!
27
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
28
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
29
Stopping Distance
• “48 vehicle pile-up on I-80 due
to fog”
• Common problem on freeways
• Stopping Distance Factors:
–
–
–
–
Perceive potential hazard
Identify unsafe situation
Make decision to stop
React by pressure on brake pedal
30
Breaking Distance?
• Reaction time
– Mental alertness
– Anticipation
– Foot on brake before
• Brakes applied
• Friction stops vehicle
– Most variables
– Tires, Road surface,
etc.
31
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………….
32
Influences to Stopping Distance
•
•
•
•
•
•
•
•
Vehicle Speed
Perception time#
Reaction time#
#driver condition
Weather
Road conditions
Weight of Ambulance
Condition of tires *
Brake condition *
*Preventative Maint.
33
Influences to Stopping Distance
• Brake ability
– Heat
– Dust
– Water
• Brake fade
– 700o liner – shoes melt
– Disc better than drum
– Less surface friction
34
Type I Ambulance
35
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
36
Type II Ambulance/Rescue
37
Type II Ambulances
Van body
· Raised roof
· Walk area between cab
and patient compartment
38
Type III Ambulance/Rescue
39
Type III Ambulances
Patient care box
mounted on Van Chassis
· Walk through between
cab and patient care
compartment
40
Following Distance
•
•
•
•
•
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
41
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
42
Read the Signs
• Highway Department Signs
• Use as guide to speed
• Pay attention to them!
–
–
–
–
Loose gravel
Congestion Ahead
Slippery when wet
Safety Corridor
43
A new line of work
• Painted surfaces are helpful
–
–
–
–
–
Fog lines
No Passing lines (and lanes)
Solid lines versus intermittent
Merging lanes and Arrows
Reflectors
44
Let’s talk just briefly on
Maintenance
• Brakes
• Tires
• Visibility (windows)
– Washer fluid
– Wiper blades
• Sirens and horns
• Panel lights
45
What about the driver
• Effect on Perception and Reaction time
–
–
–
–
–
Fatigue
Excitement
Illness
Medications
Pre-occupation/distraction
• Thinking about the call
– Horseplay
– Experience
• Know road and vehicle better
– Complacency********
46
How to make the best out of a
bad situation!
47
48
49
50