Stopping+a+Moving+Vehicle

= Stopping a Moving Vehicle  = The process of stopping a moving motor vehicle can be broken into three phases: recognition, reaction and braking. During each of these phases, the motor vehicle will travel a certain distance. The sum of these individual distances is known as the //stopping distance.// It is the stopping distance that determines whether the vehicle will be able to stop safely or not. = Recognition and reaction  = In order to stop safely, first the driver needs to recognise that there is a reason to stop. This might happen if the driver sees any of the following: a traffic light changing to red, a stop sign, a pedestrian stepping onto the road or an oncoming car swerving into the wrong lane. The time that it takes a driver to recognise the need to stop will depend on a number of factors. These include the driver’s level of alertness or distraction, fatigue, visibility, blood alcohol concentration, and driving experience.

Recognition time is difficult to measure by itself, so it is often combined with reaction time (which is the time between when a driver recognises a hazard and when the driver reacts to the hazard by braking or swerving) and given as a //recognition/reaction time//.

A moving vehicle will travel a certain distance during the recognition/reaction time. This distance is known as the //reaction distance// (‘recognition’ is dropped for convenience). Reaction distance is directly proportional to the speed of the vehicle; that is, the faster the vehicle is going, the longer the reaction distance. If a hazard is closer than the reaction distance, it cannot be avoided. Fortunately, there are few hazards that appear suddenly at such short distances. In Australia, one example is the case of a kangaroo hopping out onto a highway. e Units on pa59. See Velocity on page 570. = Braking  = Braking occurs between the instant when the brakes are applied and the moment when the vehicle comes to a complete stop. The distance the vehicle travels in this time—the //braking distance//—depends on the initial speed, the condition of the road (including surface water or ice), the condition and tread-pattern of the tyres, the amount of pressure applied to the brakes by the driver and the use of brake assistance technology like an anti-locking brake system (ABS)

= Performance Test Calculations  =


 * ** Speed ** || ** Reaction Distance (m) ** |||| ** Braking distance (m) ** |||| ** Stopping Distance (m) ** ||
 * ** (km/h) ** ||  ** m/s) **  ||   ||  ** DRY **  ||  ** WET **  ||  ** DRY **  ||  ** WET **  ||
 * 40 ||  11.1  ||  22.2  ||  6.6  ||  9.2  ||  29  ||  31  ||
 * 60 ||  16.7  ||  33.3  ||  15.6  ||  21.5  ||  49  ||  55  ||
 * 80 ||  22.2  ||  44.4  ||  28.7  ||  39.0  ||  73  ||  83  ||
 * 100 ||  27.8  ||  55.6  ||  45.5  ||  61.5  ||  11  ||  117  ||
 * 120 ||  33.3  ||  66.7  ||  66.2  ||  89.3  ||  133  ||  156  ||

= Questions  = // 1. // // What is meant by reaction distance? //  // 2. //// From the laws of physics we know that Velocity = distance / time. Re-arrange this equation to show how you could work out time if you know velocity and distance // // T = // // 3. //// What is the reaction distance of a car travelling at 11.1 m/s? // // 4. //// Work out the reaction time? // // 5. //// What factors affect braking distance? // // 6. //// Draw a scatter graph of braking distance versus speed for a car under wet conditions. // // 7. //// What is the shape of this graph? // // 8. //// Use this graph to interpolate the braking distance for a car driving at 70 km/h? // // 9. //// Examine the data and write a sentence to **compare** braking distance in DRY weather with WET weather. //  // 10. //// What is meant by stopping distance? How is it calculated? //  // 11. //// If the driver had a faster Reaction time, explain how this would affect Stopping distance? //  // 12. //// What are some of the factors that affect reaction time? //

Clearly not all cars have the same Braking distance. Braking distances for cars are measured using the standard 100 – 0 test. As the name suggests this involves measuring the distance it takes for the car to come to rest if the brakes are applied when the car is travelling at 100 km/h


 * ** Car ** || ** Braking Distance (m) ** ||
 * BMW M3 ||  30.6  ||
 * Mazda MX5 ||  31.7  ||
 * Porsche 911 Carrere ||  36.7  ||
 * Mercedes Benz C32 AMG ||  36.4  ||
 * Ford FalconXR8 ||  35.3  ||
 * Holden Monaro CV8 ||  37.1  ||

 // 13. //// Rank the cars from Best to Worst according to their Performance in the 100 – 0 test //

 14. // Make a list of all the factors that affect Stopping Distance //.