EVD
Physical Forces
EVD 2
EVDPhysical Forces
Directly Influence Control
Offer Boundaries If Maintained – safe operation If Exceeded – loss of control
Ref. Unit IV LP 1 (Lesson 8)
EVD 3
EVDPhysical Forces
Forces Acting on an Emergency Vehicle Velocity Friction Inertia Momentum Reaction Centrifugal Force Centripetal Force
Ref. Unit IV LP 1 (Lesson 8)
EVD 4
EVDPhysical Forces
Inclement Weather Excessive Acceleration Inappropriate Braking Sudden Direction change
Ref. Unit IV LP 1 (Lesson 8)
EVD 5
EVDPhysical Forces
Velocity (Speed) “Rate of change of position in
relationship to time
V = 35 feet every second (35 ft/sec) V = 55 miles every hour (55 MPH)
Ref. Unit IV LP 1 (Lesson 8)
EVD 6
EVDPhysical Forces
Velocity Control Acceleration
+ Acceleration Deceleration
- Acceleration (Coasting)
Braking Deceleration using Friction
Ref. Unit IV LP 1 (Lesson 8)
EVD 7
EVDPhysical Forces
Friction “Resistance to motion between to
moving objects that are in contact with each other.” Generates HEAT
Steering Friction Tire/Road Friction Brake Friction
Ref. Unit IV LP 1 (Lesson 8)
EVD 8
EVDPhysical Forces
Friction Tire/Road
Greatest – Stationary Ok – Motion on Dry, Smooth Road Least – Locked/Spinning
Locked – Wheel NOT turning Spinning – Wheel FREE turning
Ref. Unit IV LP 1 (Lesson 8)
EVD 9
EVDPhysical Forces
Friction Brakes
Brakes on Drums / Pads on Discs Friction Generates Heat
Heat Causes Brake Fade Will Break-down Bonding Material Heat/Expand Brake Fluid
Ref. Unit IV LP 1 (Lesson 8)
EVD 10
EVDPhysical Forces
Brakes Shoes / Drums
90%-10% / Contact-Cooling Excessive Heat = Less Contact
Pad / Disc 85%-15% / Cooling-Contact Excessive Heat = More Contact
Ref. Unit IV LP 1 (Lesson 8)
EVD 11
EVDPhysical Forces
Brakes Locking Wheels Threshold Braking
Ref. Unit IV LP 1 (Lesson 8)
EVD 12
EVDPhysical Forces
Inertia “The force it takes a moving object to
stay in motion in the same direction.”
Ref. Unit IV LP 1 (Lesson 8)
EVD 13
EVDPhysical Forces
Newton’s First Law:
The Law of Inertia
Ref. Unit IV LP 1 (Lesson 8)
“An object continues in its state of rest, or uniform motion in a straight line,
unless it is acted upon by a net external force.”
EVD 14
EVDPhysical Forces
Newton’s First Law:
The Law of Inertia
Ref. Unit IV LP 1 (Lesson 8)
Objects resist change More Mass = More Inertia
EVD 15
EVDPhysical Forces
Momentum Mass x Velocity
Ref. Unit IV LP 1 (Lesson 8)
EVD 16
EVDPhysical Forces
Newton’s Second Law:
The Law of Momentum
Ref. Unit IV LP 1 (Lesson 8)
“When an unbalanced force acts on an object, the object will be accelerated. The
acceleration will vary directly with the applied force and will be in the same
direction as the applied force. It will vary inversely with the mass of the object.”
EVD 17
EVDPhysical Forces
Newton’s Second Law:
The Law of Momentum
Ref. Unit IV LP 1 (Lesson 8)
More momentum = more energy to change
1 lb @ 1 ft/sec = 1 unit of momentum Momentum & Intertia:
WORK AGAINST THE DRIVER
EVD 18
EVDPhysical Forces
The Law of Conservation of Momentum
Ref. Unit IV LP 1 (Lesson 8)
“For a collision occurring between two objects, the total momentum before the collision is equal to the
total momentum after the collision.”
“When two objects interact, exactly equal and opposite forces result; positive and negative forces
balance out.”
EVD 19
EVDPhysical Forces
The Law of Conservation of Momentum
Ref. Unit IV LP 1 (Lesson 8)
EVD 20
EVDPhysical Forces
Reaction “For every action there is an equal and
opposite ‘reaction.’”
Ref. Unit IV LP 1 (Lesson 8)
EVD 21
EVDPhysical Forces
Newton’s Third Law:
The Law of Reaction
Ref. Unit IV LP 1 (Lesson 8)
“For every action there is an equal and opposite reaction.”
EVD 22
EVDPhysical Forces
Newton’s Third Law:
The Law of Reaction
Ref. Unit IV LP 1 (Lesson 8)
Tires push “backward” on the road Road pushes “forward” on vehicle
EVD 23
EVDPhysical Forces
Centrifugal Force An inertial force which moves a body
away from the center of rotation.
Ref. Unit IV LP 1 (Lesson 8)
EVD 24
EVDPhysical Forces
Centripetal Force Forces directing the body towards the
center of rotation. Gravity Friction
Ref. Unit IV LP 1 (Lesson 8)
EVD 25
EVDPhysical Forces
Centripetal Force vs. Centrifugal Force Forces acting in direct contrast to
Centrifugal force.
Ref. Unit IV LP 1 (Lesson 8)
EVD 26
EVDPhysical Forces
Directional Control Steering Turning “Tracking” curves
Ref. Unit IV LP 1 (Lesson 8)
EVD 27
EVDPhysical Forces
Potential Energy Capability – i.e. Coiled Spring Relative to position “Stored” energy
Ref. Unit IV LP 1 (Lesson 8)
EVD 28
EVDPhysical Forces
Kinetic Energy Relative to motion = ½mv2
m = mass v = velocity
Ref. Unit IV LP 1 (Lesson 8)
EVD 29
EVDPhysical Forces
Control ONLY
VELOCITY & DIRECTION
Ref. Unit IV LP 1 (Lesson 8)
EVD 30
EVDPhysical Forces
Control Velocity
Acceleration Change in Velocity + Acceleration = increase - Acceleration = decrease
(Deceleration) Double Mass = Double Acceleration Generally thought of in the +
Ref. Unit IV LP 1 (Lesson 8)
EVD
Vehicle Characteristics
EVD 32
EVDVehicle Characteristics
Weight GAWR
Gross Axle Weight Rating GVWR
Gross Vehicle Weight Rating
Ref. Unit IV LP 2 (Lesson 9)
EVD 33
EVDVehicle Characteristics
Weight GVW Distribution
Ref. Unit IV LP 2 (Lesson 9)
+/- 7%
2/3
1/3
EVD 34
EVDVehicle Characteristics
Weight Center of Gravity
Ref. Unit IV LP 2 (Lesson 9)
EVD 35
EVDVehicle Characteristics
Suspension Axles
Rated to carry GVW Springs
Rated to carry GVW Wheels
Load rated hub Tires
Rated to carry GVW
Ref. Unit IV LP 2 (Lesson 9)
EVD 36
EVDVehicle Characteristics
Suspension Tires
40 sq. in. Road Contact 4/32 Min. Tread
Ref. Unit IV LP 2 (Lesson 9)
EVD 37
EVDVehicle Characteristics
Brakes ABS
Wet/icy roads Works with disc and drum
Auxiliary NFPA 1901 – 36,000 lbs. Engine (“Jake”) > 20 mph Automatic Transmission Retarders Driveline Retarders
Ref. Unit IV LP 2 (Lesson 9)
EVD 38
EVDVehicle Characteristics
Water/Liquid Surge NFPA 1901 NFPA 1902 Baffling
Ref. Unit IV LP 2 (Lesson 9)