Speed And Motion

Measuring Speed

Speed is measured in metres per second (m/s), kilometres per hour (km/h) and miles per hour (mph).

To work out speed: S = D÷T (distance  ÷ time)

The faster the speed of an object, the greater the distance travelled, the shorter the time taken.

To work out distance: D = SxT (speed x time)

To work out acceleration: a = (V-U) ÷ T (where V is final speed and U is initial speed)

Speed Cameras

- Speed cameras generally take two pictures of a vehicle a certain amountain of time apart. The     position of the vehicle in relation to the distance markings on the road in the two pictures can       be used to calculate the vehicle's speed. 

Speed of car = Distance travelled between pictures ÷ Time takin between 1st and 2nd picture

Distance-Time Graphs

The slope of a distance time graph shows the increasing speed of an object. The steeper the gradient (slope), the greater the speed.

When the line in the distance-time graph is horizontal, this means that the object is moving at a constant speed.

What is Relative Speed?

e.g 1: Two cyclists are moving towards each other at the speed of 4m/s, the first cyclist sees the other moving towards him appearing to be moving towards him at a speed of 8m/s.

e.g 2: Two cyclists are moving in the same direction, the one at the font going at 6m/s and the one at the back going at 4m/s. The cyclist at the front appears to be moving away from the other st a relative speed of 2m/s, increasing the gap between them.

Speed-Time Graphs 

The slope on a speed-time graph represents the accelaration of an object. A constant acceleration increases the speed.

Thinking distance

The thinking distance is the distance travelled in between the driver realising he needs to break, and actually braking.

Sometimes, factors that affect the thinking distance are: tiredness/fatigue, medications, alcohol, road and car distractions and greater speed.

Breaking distance

The breaking distance is the distance taken for the driver to stop once the brakes are applied. 

Sometimes, factors that affect the braking distance are: bold/worn tyers, wet weather (rain), the surface and the amount of people in the car (weight).

The stopping distance can be much further for faster cars, so you need to keep your distance from the car in front (especially in bad weather) and keep to the speed limit.

Stopping distance = thinking distance + braking distance