Your kit!
GPS (Global Positioning System)
What is GPS?
The global positioning system is a satellite-based navigation system made up of a network of satellites put into orbit by the U.S. Department of Defence. GPS was originally intended for military use, but in the 1980s the government made the system available for civilian use.
How does GPS work?
GPS satellites circle the earth in a very precise orbit and transmit a signal to the earth. Your GPS receiver works out how long it took for the signal to reach it from the satellite and this tells it how far away the satellite is. By comparing the signals from 3 satellites your receiver can calculate exactly where it is on the Earth (using triangulation – ask your Maths teacher!).
Why is PEACH Project using GPS?
When we receive your GPS receiver back we can download data that tells us where and when you went outdoors. It also records how fast you were travelling and when you moved from place to place. We put your GPS data together with the data from all the other children in the study so that we can answer questions like:
- Where are children most active (school? garden? parks and playing fields?)
- How much time do children spend outdoors after school?
- Do children who walk home from school spend more time playing outdoors?
What data do you download?
The data we download consists of a table with lots of numbers on it. We can use this in complicated statistical mathematics to help us answer our experimental questions. It is possible to turn some data into maps to show how children use open spaces. Although we do this with the data from some children, so that we can use the maps in talks and on posters, we don’t do this with everybody’s data.
Can you see how having a park nearby gave this child the opportunity for lots of physical activity?
GPS facts
- There are 24 satellites in the GPS system and they are orbiting the Earth at about 20,000 kilometres above us.
- The satellites are travelling at about 11,000 kilometres per hour.
- Small rocket boosters keep each satellite on the correct path.
- The satellites are powered by solar energy and have backup batteries on board to keep them running if there is a solar eclipse.
- A GPS satellite weighs approximately 900 kilograms and is about 5 metres across with its solar panels extended.
- Each satellite is built to last about 10 years and replacements are constantly being built and launched into orbit.
Accelerometers
What is an accelerometer?
An accelerometer is an electromechanical device that measures acceleration forces such as movement or vibration. The Actigraph accelerometers we use in PEACH Project count the number of movements you make every 10 seconds and stores this as numbers. The numbers can tell us how much you were moving about during each 10 seconds that you were wearing the monitor.
How do accelerometers work?
The accelerometers use the piezoelectric effect – ‘piezo’ comes from the Greek word for ‘squeeze’ and this describes how they work. Each accelerometer contains a crystal that produces a very small electrical charge when it is flexed or squeezed. The crystal is attached to a weight and when you move, the weight wants to stay still (inertia – ask your Science teacher!). This pulls, pushes or squeezes the crystal and it produces a charge. The accelerometer also contains a chip and this records the movements so that we can download them later.
Why is PEACH Project using accelerometers?
The GPS receivers can tell us where you were active, but not how active you were when you were there. This is what the accelerometers will tell us. We will put all the data from all the PEACH children together to answer questions such as:
- How active are children?
- What time of day are children active or inactive?
- Which groups are most active? Children who walk to school? Children who live in different areas of Bristol?
What data do you download?
Similar to the GPS data, the data we download from the accelerometers consists of tables of numbers. We can put this through complicated statistics to answer some of the questions above. It is possible to turn some of the data into graphs and we sometimes do this for posters and presentations, but we don’t do it with everybody’s data.
Accelerometer facts
- The new Nintendo Wii and Sony Playstation 3 gaming systems use accelerometers in their controllers.
- IBM and Apple have recently started using accelerometers in their laptops to protect the hard drives from damage. If you accidentally drop the laptop, the accelerometer detects the fall and switches the hard drive off.
- Accelerometers are used to activate airbags at just the right time in car crashes.