# Comparing the speed of light and sound

Discussion in 'Science' started by 1nancy, Mar 5, 2011.

1. ### 1nancy

I wonder if anyone can help?
I'm a primary teacher working in Y6 and for an observed lesson in a couple of weeks time I'd like the children to investigate which travels faster, sound or light. This will be at a very basic level.
I've found an activity where you divide the class as far apart as you can - across the school field or playground. One team then shine a torch and blow a whistle at the same time. The idea is that the other team should see the light fractionally before they hear the whistle.
I know that this isn't the most scientific of investigations, but as a quick, practical way of showing that light travels faster than sound, would it work?
Usually I'd test science investigations out for myself before doing them in class, but I live by myself so this one's a bit tricky!
Thanks for any help or ideas.

2. ### 1nancy

I wonder if anyone can help?
I'm a primary teacher working in Y6 and for an observed lesson in a couple of weeks time I'd like the children to investigate which travels faster, sound or light. This will be at a very basic level.
I've found an activity where you divide the class as far apart as you can - across the school field or playground. One team then shine a torch and blow a whistle at the same time. The idea is that the other team should see the light fractionally before they hear the whistle.
I know that this isn't the most scientific of investigations, but as a quick, practical way of showing that light travels faster than sound, would it work?
Usually I'd test science investigations out for myself before doing them in class, but I live by myself so this one's a bit tricky!
Thanks for any help or ideas.

3. ### rachel_g41Occasional commenter

I've done something similar with secondary children to measure the
speed of sound. I've never tried the light/whistle thing though - how can you be sure that they're really being blown/shone at the same time?. We
burst a balloon instead - the children at a distance can both see and hear it.
You have to be a good distance apart, even at 100m the time delay is only 1/3 of a second.
We've
had some excellent results when timing this though tbh I think it's a
fluke as it's very difficult to time properly and what we measure is
more likely to be children's reaction time than actual time delay.

4. ### 1nancy

We can't be sure that they're being blown/shone at the same time, but I'm hoping that this will provide some differentiation. My higher ability children will point this out, which will provide APP evidence for some of the Sc1 skills. I can then challenge them to come up with a more accurate way of carrying out the investigation.
I like the idea of a balloon, though. I might try both as part of the same investigation.
Thanks.

5. ### phlogistonStar commenter

We used to be able to use a starting pistol - smoke and sound.
Key thing is to make the distance big enough for the sound to take a measurable / discernable time to travel. Will a balloon bursting be audible at 100m?

P

6. ### blazerStar commenter

Does the PE dept have a starting pistol or other starting device? You will need about a 100 meter distance to see/hear any appreciable difference. Of buy some fireworks and get an assistant to let one off 100m away from the class they can see the flash/smoke and then hear the bang.

7. ### rial7263

Get a large drum from the music dept. and strike it at a distance. They will see it before they hear it, give it a really good whack, (make sure you hit it and not a child), get your interviewers/observer to stand with the kids if you do not have a TA. It always works for me but beware if it's windy as it does not work then.

8. ### blazerStar commenter

You can also do it with a couple of pieces of wood. Get two 6" lengths of 2 x 2 ( 15 cm of 50mm x 50mm).

A volunteer stands about 100m away and bangs the two pieces of wood together above their head. about half a second later you hear the crack.

To measure the speed of sound we stand at the bottom of our school field. The back fence is about 95m from the building (we say it is 100m). get a volunter to clap once, you will hear the cho . Then get then to clap in rythym. They have to time their claps so that they make the second clap in time with the echo from the 1st. Once they have established a regular rythym you time 10 claps stopping the clock when you hear the 10th echo. So you have effectivly timed how long it takes sound to cover 2000 metres (10 claps 100m out and 100m back). speed = distance /Time You can usually get a good approximation of the 330 m/sec

9. ### teachsci1

If you fill it with hydrogen and oxygen it will. Not much use at a primary school as I'm guessing you won't have access to these gases.

10. ### missmunchieNew commenter

If it's a rainy day have a back up plan!
I taught speed of sound to year 9 and used the two microscopes one metre apart method, whix&iexcl;ch meant that we could do the whole lesson indoors. Anyway, this is not what I would expect someone to do in Primary.
As a plenary I showed a YouTube clip of thunder and asked the children to start their stopwatches when they saw the flash and stop them when they heard the rumble.
The clip I found had about a 2 second difference, you might be able to find some more or just show the same one a few times to get an average.
In year 9 they had to calculate the distance of the observer (camera) from the lightning, but in year 6 you just want them to notice the difference in time between the two events.