# Physics 12U - The Egg Launcher

BassMaster
Alright, so we were just assigned our ISUs for grade 12 physics, and I'm a bit confused as to what is the best design for my project.

We are to build a 'device' that launches an egg over a 1 metre tall 'fence' that is 2 metres away. The egg must then go through an 'open window' that is another 2 metres away, and then it must land in a 'fish tank'. The reason why I use quotations for some of these objects is because they may be replaced by other ones - such as the fish tank that may just be a cardboard box.

The device does not have to move, although if it DOES it can move closer to the fence and launch from a closer distance. I don't know if this will help though.

To make this more clear, here's a diagram:

http://www.freewebs.com/bassmaster4/" [Broken]

The window is 1 m tall by 0.5 m wide. The fish tank is about 0.75 m tall and 0.35 m in diameter. Keep in mind, the position of the fish tank can be anywhere from 0 to 1.5 metres from the window wall.

The <b>maximum </b> dimensions I can have on my 'device' is 1 metre by 1 metre by 1 metre.

Any suggestions?

## The Attempt at a Solution

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Gold Member
Does the egg have to survive intact?

BassMaster
No, it's a fake egg... probably rubber. It doesn't matter what velocity it hits the tank with.

Gold Member
Then build it and they will come. Really, you can slap together a launcher with a spring-loaded piston with a cup on the end to hold the "egg". Just make sure that you can easily adjust it for elevation and for spring tension and you're all set. Now here is a question that I'd like you to answer. Using your diagram of the wall, window, box, etc, what is the trajectory most likely to give you an accurate repeatable delivery? If you can, draw an arc on your diagram and repost.

BassMaster
The diagram isn't to scale. Should I make it to scale first and then draw an arc?

Gold Member
The diagram isn't to scale. Should I make it to scale first and then draw an arc?
Yes, please do. The path is short, so air resistance, etc is not going to be a big contributor, but it would be nice to see if you appreciate the ballistics involved to get the "egg" into the "tank".

BassMaster
Okay, the diagram has been changed to be relatively to scale (close enough I think). Click on the same link on my first post.

By the way, thanks for your help.

BassMaster
Also, I CAN'T move the launcher with my own hands. Something automatic has to trigger the egg launch.

Gold Member
Also, I CAN'T move the launcher with my own hands. Something automatic has to trigger the egg launch.
OK, now draw the trajectory of the egg that will make it possible for you to land the egg in the tank. For now, assume that air resistance is not a factor. This is the key to the exercise and you will have to build enough adjustment into your launcher to achieve the proper trajectory.

BassMaster
I think you may have missed my last post. I already drew the trajectory... check my diagram (use the same link that I have in the first post).

Gold Member
The trajectory does not show up in the image that I see in my browser. If you can't get the image to appear, you can describe the trajectory if you want.

BassMaster
Okay... umm... the trajectory is a parabola? Obviously we're dealing with projectile motion here.

Gold Member
Okay... umm... the trajectory is a parabola? Obviously we're dealing with projectile motion here.
And how can you maximize the on-target "hits" for your egg? How does that arc fit the limitations of your wall and your window and the placement of your target box? Describe how that "egg" has to get to the target. You can do this with little thought - you already know what the approximate path needs to look like.

BassMaster
The egg has to go over the fence, then through the window. So it first has to clear a 1 m fence. Now if my launcher is, say, 0.5 m, I need to launch the egg so that it clears the wall by at least 0.5 m. But I can't give you exact numbers... I need to draw a proper scale diagram and make some calculations, right? Like find the x and y components for velocity, displacement, etc?

Gold Member
You are confusing engineering with physics. Build the launcher, make it work, then quantify its properties if necessary. This is an exercise in practical engineering - nothing more. If you can draw a path that the projectile must take, you can design a launcher that can make it happen. The physics is encapsulated in the trajectory of the projectile. Everything else is engineering. If you understand the trajectory that the projectile must take, you are left with a simple engineering project (make it so!).

BassMaster
Okay, so if it's basically engineering how do you suggest I make it? How about a mouse-trap for a launcher, would that work? And we're also being marked on the construction (whether it easily breaks) so what kind of material should I use?

Gold Member
You can use a mouse-trap with a stop (why would you want a stop?) or perhaps you could could use a different actuator. You should consider that the mass of the platform might hurt or help you.

BassMaster
Why would the mass of the platform effect me? When you say platform you're referring to the base, right?

I'm REALLY bad at anything to do with engineering.

Gold Member
The mass of the platform may effect the accuracy of the delivery system. Can you figure out why?

BassMaster
I have no clue... seeing as how the platform is a separate entity. If the launcher is attached to the platform, I still don't see how it'll effect anything.

Gold Member
I have no clue... seeing as how the platform is a separate entity. If the launcher is attached to the platform, I still don't see how it'll effect anything.
If you eject a mass from another mass, what happens the mass that the ejection emitted from? If you were riding in the back of a pickup, and were throwing out bricks over the tailgate of the truck, what would happen to the speed of the truck?

drpizza
Or, you could just build a 20 meter tall launcher and fire the egg at 100 mph at the tank :P

BassMaster
The restriction on the size of the launcher is 1 m by 1m by 1m. Thanks for your help anyway :P.

Oh, and I have no clue what happens when you throw bricks from the back of a pickup while it's moving. Never tried it

drpizza
There are a few options that might be worth exploring: How about some sort of catapult? You can build one that uses some sort of elastic potential energy, or one that uses a weight.

Oh, and I don't think a mousetrap has enough power to toss an egg 1 meter into the air. Rat trap, maybe, but it would be pretty hard to adjust one.

harmeet_angel
Alright, so we were just assigned our ISUs for grade 12 physics, and I'm a bit confused as to what is the best design for my project.

We are to build a 'device' that launches an egg over a 1 metre tall 'fence' that is 2 metres away. The egg must then go through an 'open window' that is another 2 metres away, and then it must land in a 'fish tank'. The reason why I use quotations for some of these objects is because they may be replaced by other ones - such as the fish tank that may just be a cardboard box.

The device does not have to move, although if it DOES it can move closer to the fence and launch from a closer distance. I don't know if this will help though.

To make this more clear, here's a diagram:

http://www.freewebs.com/bassmaster4/" [Broken]

The window is 1 m tall by 0.5 m wide. The fish tank is about 0.75 m tall and 0.35 m in diameter. Keep in mind, the position of the fish tank can be anywhere from 0 to 1.5 metres from the window wall.

The <b>maximum </b> dimensions I can have on my 'device' is 1 metre by 1 metre by 1 metre.

Any suggestions?

umm.. you can use something that uses:
pressure or fluid principles
Springs

and electricity <I wonder about this one, like how you would be able to convert electricity to mechanical energy.. even if you could, you would have to do deal with complexities, perhaps.. not sure though>

so think besides using springs, pressure would be good..

putting the egg in a tube.. applying pressure form behind, and such that the egg gets fired only at certain pressure..

you can use some fluid or water for making the pressure

and so, i think... you should consider this

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abm4life
for every action there's an equal and opposite reaction :Newton's 3rd law

Therefore ,I am guessing ejecting a mass (mass 1) from another mass (mass 2 which is your platform), would make mass 2 move backwards...

But from newton's 2nd law we know F=ma... and mass is inversely proportional to acceleration. This means the greater the mass... the less acceleration. If an object with a greater mass ejects an object with a smaller mass... the force exerted by both objects on each other will be the same (in opposite directions; Newton's 3rd law). However, there accelerations will differ... meaning that the object with the higher mass won't move as much relative to the object being ejected (2nd law). So I believe it is better to use an object with a sufficient mass as a platform... ? anyone disagree with my explanation

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BassMaster
for every action there's an equal and opposite reaction :Newton's 3rd law

Therefore ,I am guessing ejecting a mass (mass 1) from another mass (mass 2 which is your platform), would make mass 2 move backwards...

But from newton's 2nd law we know F=ma... and mass is inversely proportional to acceleration. This means the greater the mass... the less acceleration. If an object with a greater mass ejects an object with a smaller mass... the force exerted by both objects on each other will be the same (in opposite directions; Newton's 3rd law). However, there accelerations will differ... meaning that the object with the higher mass won't move as much relative to the object being ejected (2nd law). So I believe it is better to use an object with a sufficient mass as a platform... ? anyone disagree with my explanation

Duh...! Is that what you guys have been trying to get at all this time? Obviously my platform will be heavier than the actual launcher. I don't want the platform being pushed back after every launch.

abm4life
The mass of the platform may effect the accuracy of the delivery system. Can you figure out why?

i was just trying to answer turbo's question. I don't know whether that was what he was trying to get at....

Gold Member
i was just trying to answer turbo's question. I don't know whether that was what he was trying to get at....
A light delivery system with a high-mass projectile will suffer from excessive recoil, which could have a very negative effect on accuracy.

abm4life
excessive recoil due to it being light, which is what i stated in my huge paragraph! :P so ye "that IS what US guys have been trying to get at all this time"!

Gold Member
excessive recoil due to it being light, which is what i stated in my huge paragraph! :P so ye "that IS what US guys have been trying to get at all this time"!
That's right. A stable platform that is far more massive than the projectile (and the delivery mechanism) will be easier to calibrate for accuracy.

BassMaster
That's right. A stable platform that is far more massive than the projectile (and the delivery mechanism) will be easier to calibrate for accuracy.

So what materials do you guys suggest I use for the platform and the delivery mechanism? And what do you suggest I use as an 'adjuster' for height and distance?

Gold Member
What do you think would work? This is an exercise designed to make you think. Give some suggestions and if you're running off-track people here will help you. I could design your launcher for you, but then you would have learned a LOT less than if you designed it yourself.