Distance and displacement
When planning a trip around NSW, you would need to consider the distance, or how far away places to visit are. you would also need to consider the amount of time you have. In this case, distance would be measured in kilometers, and your time in days and weeks.
You also need to consider where you will end your journey. Your displacement is the straight line distance between your finishing and starting points.
Speed
Speed is a measure of how fast something moves. An object moves faster when it travels a greater distances in a certain time, or covers a set distance in a shorter time.
Speed is measured in kilometers per hour.
Average speed
Average speed is a measure of how fast something moves overall. The average speed ignores the stops and changes in speed that happen in any journey and instead assumes that the object was traveling at the same speed for the whole time.
Instantaneous speed
This is the speed that you are traveling, at a specific time.
In a car the instantaneous speed is measured by its speedometer. The instantaneous speed of a car can also be measured using a mobile speed camera.
Measuring speed
There are many different ways of measuring speed. Fixed speed cameras operate using two electronic sensors embedded in a each lane of a road. A car that travels over one sensor is timed as it travels over a second sensor.
A motion sensor sends out pulses of radiation, such as ultrasonic sound waves, microwaves or infrared radiation. The reflection of this radiation from an object provides data about its position and speed.
A ticker timer is another device that can be used to measure speed. When the timer is attached to an object moving in a straight line, dots record its motion.
Speed and driving
When driving a car, it is vital to stay alert. If a child runs onto the road, or a car breaks down in front of you, you need to react and apply the brakes as quickly as possible.
The time it takes for someone to react to an emergency is known as their reaction time. For a person who is alert and concentrating, this reaction time is typically 0.15-0.3 Seconds.
Consider an emergency that happens while driving. During the reaction time the car is still traveling at the speed it was traveling at just before the emergency. A car traveling at 100km/hr will cover 4-8m before the driver even starts to apply the brakes or swerve. This distance is known as the reaction distance.
A driver’s reaction time is slowed by distractions in the car.
Distractions:
- Other people in the car
- Texting someone or speaking to them on the phone
- Changing the radio takes your eyes off the road
Additional factors such as a person’s age, fatigue and the influence of drugs and alcohol also slow a person’s reaction time.