GP yeS please

You’ll need

Rope
Access to the internet
Something to mark positions on the ground (such as cones)

Before you begin

Depending on numbers, you may need to run this activity somewhere with lots of floor space, so your ‘satellites’ can move around freely in their groups and demonstrate how the system works.

Run the activity

Explain that everyone will be working together to demonstrate how the Global Positioning System (GPS) works. They’ll be doing this by finding a lost person.

The lost person will send signals to different satellites to measure the distance they are from them. For the purpose of his activity, groups can count steps to measure distance between satellites and the lost person.

Split into groups of four. Each group should move into some space and choose one person to be lost somewhere on Earth. The other three will be GPS satellites.
In each group, one satellite should position themselves somewhere in the activity area. The lost person should position themselves five steps away from that satellite. Both should take a length of rope the same distance as the space between them, and each holds an end.

Each person in each group could use a marker to remind them where they were standing, if they’ve had to move to get rope.

Holding onto the rope and keeping it fairly taut, the lost person should walk in a circle around the satellite. When everyone’s doing this, the person leading the activity should point out that this signal indicates that the lost person is somewhere within the circle. This isn’t very precise, so a second satellite is needed.
One of the other satellites in each group should stand on a spot about one step outside the five-step-sized circle. The person leading the activity should explain that the second satellite is six steps from the lost person. The lost person in each group should put down the first length of rope.
The second satellite and the lost person should take a length of rope the same length as the distance between them. Holding onto the rope and keeping it fairly taut, the lost person should walk in a circle around the satellite. When they reach the first rope where it was left, the lost person should stop and pick that up too.
The person leading the activity should explain that the lost person is now somewhere that’s five steps from the first satellite and six steps from the second. This limits the number of possible locations that the lost person can be. Adding a third satellite can narrow down the location even more.
The third and final satellite in each group should start at a point the same distance between from each of the other two satellites, so that they form a triangle shape. The lost person should put down their ends of rope. The person leading the activity should point out that this leaves them about five steps from the lost person.
The third satellite and the lost person should take a length of rope the same length as the distance between them. Holding onto the rope and keeping it fairly taut, the lost person should walk in a circle around the satellite until they reach the first and second ropes, which they should pick up.
The third distance allows us to ‘triangulate’ the position of the lost person. This involves making a triangle of points, the centre of which should be the lost person’s precise location. In the activity area, this should be the only spot where the lost person can hold all three lengths of rope.
Bring everyone back together and congratulate the groups on finding their lost friend!

Reflection

This activity explored the Global Positioning Satellite system. Does anyone know who owns the system? The GPS system is owned by the United States government, but is actually one of several systems known as the Global Navigation Satellite System (GNSS). Other countries that own satellite systems include China, France and Russia. India has a regional satellite system that only covers part of the globe (centred on India). Given what you now know about how GPS works, why might it be necessary for different countries around the world to control multiple satellites?

The accuracy of GPS can be affected by outside factors. The number of satellites that are able to provide a signal where you are, usually needs to be three or four to get a reading. Tall buildings, mountains and trees can affect the signal, as they block the line of sight between the satellite and GPS device. Those who were lost in the activity, imagine a huge mountain just appeared between you and the rope you were about to pick up. It might be time to head for more open ground.

The GPS system has changed how people find their way. Satellite navigation systems in cars and commercial vehicles rely on GPS. They help people explore new places safely and get deliveries to their destinations. GPS not only helps people know where they are, but it can be used by the emergency services to find lost or injured people. GPS is also used in scientific experiments, tracking markers left in the oceans or migrating birds. What other applications can you think of for GPS? Think about how it could be used to make a difference in education, business or to wider society?

Safety

All activities must be safely managed. You must complete a thorough risk assessment and take appropriate steps to reduce risk. Use the safety checklist to help you plan and risk assess your activity. Always get approval for the activity, and have suitable supervision and an InTouch process.