Measuring Motion

Measuring Speed

There are a number of ways speed can be measured in the lab. One such way uses light gates, with the set up shown below.The air track helps to minimise friction so that the speed is as constant as possible.

• The vehicle is pushed with a given force and it travels through the light gates.
• Inside the light gate there is a beam of light that the card on vehicle cuts through.
• At this point the timer starts and then stops once the light is detected, this happens when the vehicle has travelled through the light gate.

﻿﻿Since we know the time it took, as well as the length of the card (measured before or after) we can use these two quantities to calculate the speed.

Typical Speeds

Typical speeds of various things vary due a number of reasons. These can include age, fitness, weather, terrain and distance travelled. Nonetheless there are some values you are expected to know:

It is not only moving objects that have varying speed. The speed of the wind and the speed of sound also vary. A typical value for the wind is about 12 m/s and the speed of sound in air is about 330 m/s.

What is the typical speed of the wind?
12m/s
Explanation: Don't forget to include units
A student says that cars typically travel at 70mph - is this true?