Radar is the detection of objects using radio or sound waves which bounce back off an object in its path. Eighty years ago radar was first developed and six years later it helped to change the course of the Second World War and, in particular, helped the RAF win the Battle of Britain.
Radar has been around since bats evolved so the scientists had only to discover a way of directing sound waves and then a way to interpret their reflection.
In these activities, the pupils will gain an understanding of how sound helps us to locate position and how echoes are formed.
Year 3 to Year 6
- Understand how we can locate the position of a person or sound using the stereo capability of our ears
- Recognise that sound is reflected off some surfaces to form echoes
- Learn how bats use echo location to navigate and find their food
It’s often said that when we lose the use of one or more of our senses, others are heightened. In this activity the pupils will be able to test the theory and see if they can detect a solid object in a room just through sound.
This doesn’t work with everyone so you may have to try it on a few students.
You’ll need to be in a room with no furniture and nothing that absorbs sound like curtains or carpet – the school hall will do.
Ask the class to sit silently on one side of the hall then blindfold a volunteer, move them randomly around the hall to disorientate them then ask them to clap, one clap at a time and listen to the sound before taking a step forward. Repeat this and they should find that as they approach a wall, the sound changes. Make sure someone walks with them to stop them falling or walking into a wall. What is happening is that sound waves diffuse in the air but as you approach a solid object, the sound wave has a much shorter distance to travel, reflect and travel back to your ears making the sound clearer.
Bats use a similar technique to locate obstacles to their flight and to detect small objects close by which might be food.
Few people realise why humans have two ears and why they’re placed where they are on our heads. In this activity, the pupils will gain an understanding of why two ears are better than one!
Blindfold a pupil and ask them to stand in the middle of a room. Ask them to place a hand firmly over one ear. Now ask another pupil to stand around four metres away in any direction from the blindfolded pupil and say “Hi”. Ask the blindfolded pupil to point to where the sound was coming from. Invariably, the direction they indicate is incorrect. Ask them to change which ear is covered and to repeat the process. You’ll find the same result occurs.
When both ears are uncovered, most pupils will be accurate in determining where the sound came from.
This works very similarly to how we judge distance and position with our eyes; by triangulating the position of the sound and the direction of travel of the sound waves to our ears.
In a big room such as a school hall or sports hall where there are solid, flat surfaces and no sound deadening material, you’ll find that sound echoes.
Ask the pupils to stand at one end of the hall and ask one of them to clap once. They should hear the sound of their clap followed shortly after by the reflected sound of the clap – this is what we call an echo.
Tell the pupils that the sound is travelling towards the wall as a wave and being bounced or reflected off it, similar to how an ocean wave bounces off a harbour wall or a rock.
Ask them why they think they hear the echo slightly after the initial clap. The delay is the time that the sound wave takes to reach the wall and reflect back to our ears. The speed of sound at sea level is 340m per second so if you are 20m from the reflecting wall, the sound will take about a ninth of a second to return – enough time for us to hear the delay and therefore the echo.
Ask the students to try the clap in different parts of the hall, facing flat surfaces, into corners or lying down, facing up into the air. Does this make a difference to what they hear?
In a large enough room, the pupils might hear multiple echoes, gradually fading out. Ask them if they can explain why this is (the waves keep reflecting off walls in front of us and behind us, losing some energy each time before returning to our ears.