Transcript Chapter 5

5.1 GRAVITY AND ENERGY OF MOTION
Gravity
 Is a force that pulls all objects toward the center of earth
 Effects of Gravity
 When you drive uphill your car can lose speed as it works against the force of
gravity. You must increase power (accelerate) to maintain speed
 The force of gravity also tends to increase the speed of cars going downhill. You
need a longer distance in which to stop.
5.1 GRAVITY AND ENERGY OF MOTION
Center of Gravity
 The point around which all an object’s weight is evenly balanced
 Most cars have a low center of gravity so they will handle well in turns
 A car will handle differently when its center of gravity is raised. It will be less
stable in curves and during quick maneuvers
5.1 GRAVITY AND ENERGY OF MOTION
Energy of Motion (Kinetic Energy)
 The energy an object has because it is moving
 The faster a car moves the more energy of motion it will have. The car will be
harder to control
 Mass=Weight A vehicle’s energy of motion doubles when its weight doubles.
When the vehicles weight doubles, the vehicle needs about twice the distance to
stop
 Velocity=Speed A vehicle’s energy of motion is proportional to the square of its
increase in speed. When the vehicle’s speed doubles, the vehicle needs about
four times the distance to stop. When, the vehicle’s speed triples, the vehicle
needs nine times the distance to stop.
 Kinetic Energy Video - http://www.youtube.com/watch?v=vl4g7T5gw1M
5.2 FRICTION AND TRACTION
Friction
 The gripping action which keeps, each tire from slipping when the tires rest or move on the road
Traction
 Friction or gripping power between a tire and the road. Traction allows a car to grip the road so
it can speed up, slow down, and turn
 http://www.youtube.com/watch?v=06W4qvhZEEc
Tread
 The grooved surface of a tire that grips the roadway. In rain it allows the water to flow through
the grooves and away from the tire
 Bald tires – worn out tread
 Overinflated – only the center of the tire provides traction
 Underinflated – only the outside edges of the tire provide traction
 Two areas of the roadway that freeze first – bridges, shady areas
 Show Video –Advanced Auto Parts (Tire Safety – 1:21 min) or
http://www.youtube.com/watch?v=zA6MUlVNkLM
5.2 FRICTION AND TRACTION
Curves – Factors that affect the control you have over your car in a curve
 Speed – adjust speed before entering the curve. Follow any posted advisory speed
limit signs
 Sharpness of a Curve – use lower speeds for sharper curves
 Bank of a Curve – a curve that is higher on the outside than it is on the inside. This
tilt improves control by working with the force of gravity
 Load – a vehicle’s load determines its ability to handle curves
 http://www.youtube.com/watch?v=1STGU6BeND8
BANKED CURVE
5.3 STOPPING DISTANCE
Total Stopping Distance
The total distance it takes to stop a car
Includes:
Perception distance
+ reaction distance
+braking distance
=total stopping distance
http://www.youtube.com/watch?v=mDWCen_09o8
5.3 STOPPING DISTANCE
Factors that affect braking distance
 Speed
 The higher the speed, the longer the braking distance
 Car Condition
 Cars with worn tires, bad shock absorbers, old brakes need a longer distance to
brake
 Roadway Surface
 Rain, snow, ice, gravel, leaves – increases braking distances
 Driver Reaction
 Hills
 Load
5.4 CONTROLLING FORCE OF IMPACT
Force of Impact
 The force with which one moving object hits another
Three factors determine how hard the force of impact will be when a car hits another
object
 Speed
 Weight
 Distance between impact and stop
5.4 CONTROLLING FORCE OF IMPACT
10 Safety Devices that protect you in an accident
Seatbelt
Air Bag
Front and Rear crush areas
Energy Absorbing bumpers
Side door beams
Reinforced Windshield
Energy Absorbing steering wheel and column
Padded Dash
Head Restraints
Child safety seats
Drive Right Video Chapter on Natural Laws