In this STEM activity, students have to design and build a contraption that automatically bursts a balloon when a person walks through a trip wire which triggers the contraption. The trip wire isn’t there to trip the person walking; it’s there to be tripped and to trigger the contraption.
To build their contraption, students can use retort stands, boss-heads, clamps, rulers, cups, plasticine, icy-pole sticks, sticky tape, straws, pins, string, and, of course, a balloon.
Watch the 6-minute video that explains the task!
Watch the Teacher Guide on Vimeo on Demand. It contains lots of examples of the amazing contraptions that students have designed and built over the years and it gives teachers who want to run this activity plenty of tips.
The Teacher Guide is free for all teachers.
Just send an email to learning@liacoseducationalmedia.com and we’ll send you a Promo Code that will allow you to view the Teacher Guide for free. (Please use your school email address, not a gmail account or anything like that!)
The Trip Wire Balloon Bursters activity is quite similar to the Gallipoli Balloon Bursters activity so be sure to check that out if you haven’t already seen it. Both require a fair amount of engineering.
A Gallipoli Balloon Burster is a water-powered contraption that automatically bursts a balloon after a small time delay. It’s based on the “drip rifle” which was set up by Australian and New Zealand Army Corps soldiers in the trenches of Gallipoli in World War I.
The Drip Rifle hurt no-one but it saved thousands of lives!
Below is (more or less) the transcript of the Trip Wire Balloon Bursters Instructions video.
In this practical activity, students have to design and build a contraption that automatically bursts a balloon when a person walks through a trip wire which triggers the contraption. The trip wire isn’t there to trip the person walking; it’s there to be tripped and to trigger the contraption.
This is just one example of a set up but I’ve pixelated the contraption itself because it’s best if you design and build your own of course.
Trip wires are used in a variety of settings. For example, soldiers in a jungle who have to set up a camp at night, sometimes surround their camp with a series of trip wires that are attached to hand grenades.
A grenade is attached to a tree, not with sticky tape like I’m doing here but with a thin metal strap and the trip wire is attached to the grenade’s pin. The other side of the trip wire is attached to another tree.
If an enemy soldier walks between the trees and pulls on the trip wire, the trip wire pulls on the pin, which triggers the grenade, and the grenade explodes. I just can’t imagine what it would be like to be a soldier.
This footage shows some soldiers doing a training exercise. They’re not using grenades here but rather a device called a trip flare. Using flares is much safer than using grenades, because grenades can accidentally be triggered by the same soldiers that set them up!
Let’s look at another example of the use of trip wires.
This is the Saturn V rocket that carried astronauts to the moon in the late 1960s and early 1970s. The small command module near the top was where the astronauts sat. The rocket was built with a series of trip wires running up the side which were attached to the Launch Escape System which was basically a small rocket attached to the command module.
In the event of an emergency like an explosion of the main rocket the trip wires along the side of the rocket would be cut and that would trigger the Launch Escape System to fire and to carry the command module and the astronauts inside away from the explosion.
It turns out that they never needed it, but in this test flight we can see the system in action. The test rocket lifting an uncrewed command module starts breaking up, which severs the wires (which we can’t see here in this footage) and the Escape System fires, carrying the command module away from the disintegrating rocket. Once clear, the escape rocket detaches, and the command module deploys its parachutes.
Launch Escape Systems are still used but it’s much more common today for them to use electronic sensors.
Trip wires are also used in some industries. Conveyor belts in large factories often have trip wires running along them (which are also called pull cords). If an emergency arises anywhere along the conveyor belt, workers can pull on the trip wire, which activates the emergency switch, which stops the conveyor belt.
Now we don’t have any conveyor belts, rockets, or grenades, but we do have balloons to burst. You can think of the activity as a trap for your little brother or sister who always sneaks into your bedroom, when you’re in, say, the loungeroom. A trip wire is pulled, which results in the balloon bursting so you’ll get alerted and they’ll get a big shock.
To build your contraption, you can use retort stands, boss-heads, clamps, maybe some rulers, cups, some plasticine, icy-pole sticks, sticky tape, maybe some straws, and definitely pins and string, and of course a balloon. and rulers, and anything else handy such as the chairs and tables in the room.
Your contraption can make use of gravity (that is, it makes something fall) or use a lever of some description or anything else that you can think of. I’ve done this activity with probably 50 or more different classes and I’ve seen lots and lots of different designs.
Now some rules and tips.
- A little balloon is very difficult to pop. A large balloon is very easy to pop.
- The string should be placed quite low at about shin height and the balloon has to be over on one side, not directly in front of the person walking.
- Plasticine can help with securing a pin or pins to your contraption, but there are plenty of other ways as well of course.
- Don’t expect the balloon to sit still if it’s just resting on the floor. Even a little wind can push it away. It’s best to secure it with, say, some retort stands or some chairs.
- Be prepared for a few failures first. That’s completely normal in any kind of engineering process.
- The person walking has to test the contraption by just walking normally.
- Once you’ve had a successful pop, you have to do it a second time to prove that it wasn’t just luck.
- Lastly, you won’t be given a balloon until your teacher thinks that you’ve got a workable design that you’ve kind of tested.
So, when your teacher gives you the go ahead, you can begin.
Teacher Guide:
The Teacher Guide shows lots of examples of Trip Wire Balloon Bursters that my students have devised over the years.
Since the 1990’s, when I first did this activity, I’ve seen hundreds of different designs.
- I always get them to test a prototype before I give them a balloon because I don’t want them blowing up a balloon first and then playing balloon tennis for twenty minutes.
- I typically give students a double period to design, construct, and test their Trip Wire Balloon Bursters, or in other words, about an hour and 40 minutes.
- If students have two successes in a row, which is fairly common, I usually, if there’s time, get them to modify their balloon bursters to burst two balloons with the one trip wire.
- You have to move chairs and tables around and it can be a little tight in some rooms, but the students really enjoy this activity.
- There are usually multiple failures, followed by multiple tweaks and modifications. I’ll often help kids if they’re stuck by making suggestions.
- Whenever a group does a trial I usually announce it to the class and I always tell the students to call me over so that I can see their Balloon Bursters work. I tell them, only half-jokingly, that if I didn’t see it, it didn’t happen!
- There’s often a little bit of industrial espionage that goes on, but I don’t really mind.
So good luck with it.
Watch the Teacher Guide on Vimeo. Change Vimeo on Demand. It contains lots of examples of the amazing contraptions that students have designed and built over the years and it gives teachers who want to run this activity plenty of tips.
The Teacher Guide is free for all teachers.
Just send an email to learning@liacoseducationalmedia.com and we’ll send you a Promo Code that will allow you to view the Teacher Guide for free. (Please use your school email address, not a gmail account or anything like that!)
The footage used in the video showing trip flares and hand grenades come from these US military videos:
https://www.youtube.com/watch?v=8xtaUyTj20Y&ab_channel=DefenseFlashNews
https://www.youtube.com/watch?v=qvBYjCmLQig
All the footage of rocket launches was produced by NASA.
This photo, used to illustrate the use of trip wires (also called pull cords) on conveyor belts, came from Banner Engineering. This site explains the use of these essential safety devices.
https://machinerysafety101.com/2018/08/28/emergency-stop-pull-cords/