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EVD Physical Forces EVD Physical Forces Directly Influence Control Offer Boundaries If Maintained – safe operation If Exceeded – loss of control Ref. Unit IV LP 1 (Lesson 8) EVD 2 EVD Physical Forces Forces Acting on an Emergency Vehicle Velocity Friction Inertia Momentum Reaction Centrifugal Force Centripetal Force Ref. Unit IV LP 1 (Lesson 8) EVD 3 EVD Physical Forces Inclement Weather Excessive Acceleration Inappropriate Braking Sudden Direction change Ref. Unit IV LP 1 (Lesson 8) EVD 4 EVD Physical 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 5 EVD Physical Forces Velocity Control Acceleration + Acceleration Deceleration - Acceleration (Coasting) Braking Deceleration using Friction Ref. Unit IV LP 1 (Lesson 8) EVD 6 EVD Physical 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 7 EVD Physical 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 8 EVD Physical 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 9 EVD Physical 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 10 EVD Physical Forces Brakes Locking Wheels Threshold Braking Ref. Unit IV LP 1 (Lesson 8) EVD 11 EVD Physical 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 12 EVD Physical Forces Newton’s First Law: The Law of Inertia “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.” Ref. Unit IV LP 1 (Lesson 8) EVD 13 EVD Physical Forces Newton’s First Law: The Law of Inertia Objects resist change More Mass = More Inertia Ref. Unit IV LP 1 (Lesson 8) EVD 14 EVD Physical Forces Momentum Mass x Velocity Ref. Unit IV LP 1 (Lesson 8) EVD 15 EVD Physical Forces Newton’s Second Law: The Law of Momentum “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.” Ref. Unit IV LP 1 (Lesson 8) EVD 16 EVD Physical Forces Newton’s Second Law: The Law of Momentum More momentum = more energy to change 1 lb @ 1 ft/sec = 1 unit of momentum Momentum & Intertia: WORK AGAINST THE DRIVER Ref. Unit IV LP 1 (Lesson 8) EVD 17 EVD Physical Forces The Law of Conservation of Momentum “When two objects interact, exactly equal and opposite forces result; positive and negative forces balance out.” “For a collision occurring between two objects, the total momentum before the collision is equal to the total momentum after the collision.” Ref. Unit IV LP 1 (Lesson 8) EVD 18 EVD Physical Forces The Law of Conservation of Momentum Ref. Unit IV LP 1 (Lesson 8) EVD 19 EVD Physical Forces Reaction “For every action there is an equal and opposite ‘reaction.’” Ref. Unit IV LP 1 (Lesson 8) EVD 20 EVD Physical Forces Newton’s Third Law: The Law of Reaction “For every action there is an equal and opposite reaction.” Ref. Unit IV LP 1 (Lesson 8) EVD 21 EVD Physical Forces Newton’s Third Law: The Law of Reaction Tires push “backward” on the road Road pushes “forward” on vehicle Ref. Unit IV LP 1 (Lesson 8) EVD 22 EVD Physical Forces Centrifugal Force An inertial force which moves a body away from the center of rotation. Ref. Unit IV LP 1 (Lesson 8) EVD 23 EVD Physical Forces Centripetal Force Forces directing the body towards the center of rotation. Gravity Friction Ref. Unit IV LP 1 (Lesson 8) EVD 24 EVD Physical Forces Centripetal Force vs. Centrifugal Force Forces acting in direct contrast to Centrifugal force. Ref. Unit IV LP 1 (Lesson 8) EVD 25 EVD Physical Forces Directional Control Steering Turning “Tracking” curves Ref. Unit IV LP 1 (Lesson 8) EVD 26 EVD Physical Forces Potential Energy Capability – i.e. Coiled Spring Relative to position “Stored” energy Ref. Unit IV LP 1 (Lesson 8) EVD 27 EVD Physical Forces Kinetic Energy Relative to motion = ½mv2 m = mass v = velocity Ref. Unit IV LP 1 (Lesson 8) EVD 28 EVD Physical Forces Control ONLY VELOCITY & DIRECTION Ref. Unit IV LP 1 (Lesson 8) EVD 29 EVD Physical 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 30