science teacher needs help

If you are the science teacher sending students to my college, I'd suggest that you take an English I class that teaches you how to spell "matter", "aluminum", "opened", and "sufficient".

Also punctuation, but I guess I can't expect that from a high school teacher.

Jim

Elementary school actually, sorry, I'm tired it has been a long day. Thanks for your help with my spelling and punctuation and complete lack of assistance on my problem.

The projectile must be detected by light. For example an LED light source on one side and a photodetector on other. Then some transistors that turn on - amplify - increase current - to trip the relay when light bean is interrupted. Sorry, but you will need some basic electronic knowledge.

Build> Elementary school actually, sorry, I'm tired it has been a long day.

Actually the identical demonstration was televised in a lecture on introductory physics to a lecture class at Cal Tech. His series is regularly televised on the (oh Lord, we have a spelling critic present in our readership) but still I'll give it a try. It was on the Annenberg Foundation's (sp?) education channel on cable.

He used a an electro-magnetically suspended doll and a simple suction-cup plunger projection plastic gun to demonstrate this rather basic point: All objects accelerate and fall at the same rate, whether or not they have an initial horizontal velocity.

In this demonstration it appered that he had used nothing more complex than a simple microswitch attached to the gun's trigger to open the circuit powering the suspension magnet. No additional electronic are either required nor desired for such a simply demonstration.

And yes, he hit the target about 3/4 of the way down before it hit the ground!

Cute demonstration, but very basic and I would seriously doubt that it would convey any knowledge of significance to as elementary school audience.

Hope this helps... Harry C.

Use an optical switch - These are sometimes used on shop doors. They typically work by bouncing a beam of light or IR light from a reflector. When someone walks through the beam it's broken and a bell sounds.

^^^^^^^^ aluminium

Ian

Your foil carries current to a relay that holds a set of contacts open until the foil breaks . . . not much of a circuit. I think you'd want to try that idea for problems too. I imagine the foil may deflect the projectile also.

You might ram the projectile out of the barrel with a pneumatic cylinder and have it make a connection when it protrudes past the barrel.

Use a different projectile - a ball bearing drops down a long groove and is deflected upward by a bend in the groove and shorts a set of contacts inlaid into the guide groove. (or inlaid into the barrel of your air gun if the projectile can be conductive)

A photo switch is the obvious choice.

Surplus center has a nice one for $19.95 Tiny physical / beam size and good range.

• Supply voltage 10-30 VDC * 150 mA current switching rating * Visible red beam * NPN sinking output * 8 m (26 ft.) max. range * Two bolt mounts on 1" centers * Size of each: 15/16" x 1/2" x 1-3/8"

The circuit is maintained while the beam is intact and opens when blocked so you'd still need a relay - of 80 ohms or greater coil resistance if run at 12 volts

Surplus Center puts out a pretty good paper catalog with all manner of interesting tinker toys. American Science and Surplus is another inexpensive toy source. I don't see any photo switches though.

Another idea; Drop the blow gun for a catapult and let the catapult arm close a switch when it reaches the end of its travel. Simple and inexpensive.

A small wind up spring or different springs for different velocity or weight projectiles.

Yes I saw this demo in A101 physics at college. It used a tin can for the target and a small ball bearing shot out of a spring powered cannon for the projectile. If you did the same it would trivialize the switch problem. I actually remember this experiment quite vividly and it was very dramatic as the projectile and target were at opposite sides of the lecture room. The distance was around 40' and the little cannon was quite powerful. Richard

The Golden Rule: "He with the gold gets to make the rule." http://66.102.7.104/search?q=cache:890Ux45HUjsJ:en.wikipedia.org/wiki/Aluminum+handbill+*-domination-of-production-of-the-metal+Charles-Martin-Hall

Thanks, I am looking into a photoswitch arrangement. I have an older student whho is looking into using a LEGO light sensor as a possibility. I need to finish this project by Friday so ordering something throught the mail is not possible.

http://66.102.7.104/search?q=cache:890Ux45HUjsJ:en.wikipedia.org/wiki/Aluminum+handbill+*-domination-of-production-of-the-metal+Charles-Martin-Hall

Wikipedia is real swell but not The Oracle; for the moment can't we just agree that outside North America it's 'aluminium'? Sheesh!

Ken

No Ian, it's "aluminum" and not "aluminium." See for example:

Kindest regards, Harry C.

It's aluminium.

Cheers.

Ken

("Let's call the whole thing off")

Cheers.

Ken

What amazes me sometimes is the way teachers ignore the opportunity to 'teach' kids to think, and to solve problems.

This project seems to be an ideal one for the kids to derive a solution, help with the design, and then test the gear and the theory it demonstrates.

I would be most surprised if the kids weren't able to rig a simple circuit for such a device,

David - who shakes his head > I need a simple solution for a classroom science project. I am a

suggest

This is a demonstration for a 5th grade science class.

They have constructed a majority of the apparatus, but have been stumped (me too) as to how to solve the trigger problem.

What level of technical expertise do you think 10 year olds have to find a solution for a problem such as this?

It needs to be completed by Friday (as stated earlier).

Rick - who shakes his head at the presumption and arrogance of some people

It doesn't mean it, but it is spelt that way (-ium) in most English speking countries.

Bye. Jasen