ANZAC soldiers used Drip rifles to trick the Turks during the evacuation of the Gallipoli peninsula. The idea was simple and clever.

Two kerosene tins were placed one above the other. The top tin was full of water and the bottom tin, with a trigger string attached to it, was empty.

At the last minute small holes were punched in the top tin. Water would drip into the bottom tin.

When the bottom tin became heavy, it would drop downwards pulling the trigger string with it and the rifle would fire.

Lots of drip rifles were timed to go off at different times to give the impression that the ANZACs were still in the trenches. In actual fact they were creeping down to the beaches to escape.

Drip Rifle at Bandiana 2007.jpg
Source: empirecall.pbworks.com
drip rifle 2
Source: www.abc.net.au

An Interesting Investigation...

Your challenge is to build a machine which uses two tin cans, one dripping into the other, as a time-delay switch to make something happen.

Here's what we came up with in the Allen Centre...

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BANG Model 1

Note the safety screw beneath the pin arm which is pulled out once the machine

is set up and ready.

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bang

BANG Model 1: How does it work?

Ask yourself a few questions to work it out...

The top tin can is dripping water into the bottom tin can, drip... drip... drip...

1. Why does the model use a cord for the water to drip down instead of just a hole in the tin?

2. What sequence of events happens when the bottom tin can gets heavy and drops down?

3. What is the purpose of the rock on the see-saw arm?

4. Why is there a nut on the arm holding the pin?

5. The two arms are attached by a string, hooked over a tiny nail at the end of the see-saw arm. Why?

6. What is the purpose of the screw at the top of the loop of string?

7. How critical is the position of the pin?

8. What size of the balloon makes the loudest BANG? Why?


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BANG Model 2

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bang

BANG Model 2: Much simpler but just as effective...


Now that you've worked out how BANG Model 1 works you will appreciate how much simpler is

BANG Model 2. You will also have worked out the purpose of the stone on the end of the arm.

So... a few more questions...

1.There's a nifty little handle attached to the bottom tin. Why?

2.The drip-cord is placed at the back of the tin instead of in the middle. Why?

3. When the bottom tin gets heavy, what is the sequence of events that pops the balloon?

4. What is the purpose of the screw beneath the arm?

5. What would be the effect if the screw through the arm was positioned closer to the stone?

6. What are the variables which could affect the timing of the BANG?


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Andrew's machine design...