Measuring Speed (AQA GCSE Physics)

• The table below gives some typical speeds (in m/s) for various everyday scenarios

Typical Speeds Table

• Note that typical speeds of a person walking, running or cycling depends on a variety of factors, such as:
  • Age
  • Terrain
  • Fitness
  • Distance

• Similarly, typical speeds of transportation systems like cars or planes will depend on their:
  • Shape
  • Design
  • Cost
  • Purpose

Part (a)

• • The student’s claim is incorrect because 6 m/s is too fast
  • The typical speed that people walk at is about 1.5 m/s

Part (b)

• • Some factors that can affect the typical speeds of a person walking are:
    • The terrain might be wet, rocky or steep
    • The age of the person
    • The fitness of the person
    • The length of the walk or journey

• Moving objects aren’t the only things that have varying speeds
• The speed of sound and the speed of the wind also vary
• A typical value for the speed of sound in air is 330 m/s
  • Interestingly, the speed of sound in seawater is much faster, typically around 1500 m/s

• Speed is the distance travelled by an object every second
• The simplest way to measure the speed of an object, is to time how long it takes to travel a known distance and use the equation:

Choosing Equipment

• To ensure a result for speed is as accurate as possible, choose the appropriate equipment to measure the distance and time

Some simple equipment that can be used to measure distance and time

• To compare the average falling speed of a tennis ball to a plastic cone, for example, you could use:
  • A metre rule to measure the distance they fall from
  • A timer to measure how long they take to reach the ground

• It would not be practical to use a metre rule to measure the length of an athletics track though
• In this instance, a more appropriate piece of equipment would be a (long!) tape measure, or even better, a trundle wheel

A trundle wheel is ideal for measuring long distances

Using Lights Gates to Measure Time

• Light gates are pieces of digital equipment that allow times to be measured more accurately

Light gates can be used to accurately time the motion of objects in a laboratory

• A light gate can be used to start a timer when an object passes through it
• A flag on top of the moving object blocks a beam of light as it passes through the light gate, triggering the timer to start
• A second light gate (at some fixed distance away) can be used to stop the timer as the object passes through it

Single Light Gates to Measure Speed

• A single light gate can also be used to measure the speed of an object as it passes through

Example of using a single light gate to measure speed

• The timer measures how long the light gate is blocked for
• The distance travelled is given by the length of the flag passing through the light gate
• The two measurements for distance travelled and time taken can then be used in the equation for speed