Physics Project Ideas for this Competition please (self-propelled car)

[Roberta314]

Homework Statement

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Relevant Equations

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Hey guys I'm currently working on a school physics project and I need some ideas for it. So basically the goal of the project is to create a vehicle that has to propel itself forward by firing a projectile backwards.

The vehicle will be judged based on a scoring system that includes 3 criteria:
1. Distance - the car must travel at least 6m to get max score for distance.
2. Time delay - after I trigger the car, there must be a 5 second delay before the projectile is launched, the closer the time delay is to 5s the higher the score for this criteria. (I have no clue what how to accomplish this)
3. Combined mass - the car and the projectile will be weighed together, and the lighter they are the higher the score.

Although there are a few other requirements:
1. The projectile must end up behind the start line.
2. The projectile must start on the vehicle, so not touching the ground.
3. The total mass of the car and the projectile must not exceed 1kg.
4. No electronics or explosives.

 

[berkeman]

Welcome to the PF, Roberta.

What are your thoughts so far? What kind of optimizations can you think of, given the constraints?

There must be other requirements/constraints as well, right? For example, I doubt you are allowed to use small explosive charges to propel the weight off the back of the car, right?

2. The projectile must start on the vehicle, so not touching the ground.Attach files

Also, if you tried to attach a file, it did not attach/upload correctly. Maybe try again? Thanks.

 

[Roberta314]

Welcome to the PF, Roberta.

What are your thoughts so far? What kind of optimizations can you think of, given the constraints?

There must be other requirements/constraints as well, right? For example, I doubt you are allowed to use small explosive charges to propel the weight off the back of the car, right?
Also, if you tried to attach a file, it did not attach/upload correctly. Maybe try again? Thanks.

Oh yes thanks for reminding me I just edited the requirements. And the attachment must have been an accident I didn't want to attach anything.

 

[berkeman]

Are there max/min dimension requirements? Or just the max weight? Can you think why that is an important question to ask?

 

[Roberta314]

Are there max/min dimension requirements? Or just the max weight? Can you think why that is an important question to ask?

There are no dimension requirements other than the max weight. So far I can only think ways to launch the projectile (catapult, sling shot, spring, etc.). My thought is that if I can launch a heavy projectile at a decently fast speed which keeping the car light it will travel faster and further. Also I can't think of anything that I can do to achieve that 5 second delay.

 

[berkeman]

Two hints:

-1- Have you seen the movie "The Wrath of Khan"? If so, do you remember Spock's tactical comment to Captain Kirk when Khan was chasing them in the nebula?

Spoiler

Also I can't think of anything that I can do to achieve that 5 second delay.

-2- There used to be a game called "Mouse Trap" a long time ago (when I was a kid) that had a mechanism that you might be able to use as a basis for your 5-second delay mechanism...

https://i.redd.it/geejcv3e3wl21.jpg

 

[David Lewis]

A clockwork Tomy Timer [http://waterrocket.uh-lab.de/tomytimers.htm], or Silly Putty rotary friction timer [] are common time delay mechanisms. In the old days, they used a slow-burning fuse.

 

[Roberta314]

A clockwork Tomy Timer [http://waterrocket.uh-lab.de/tomytimers.htm], or Silly Putty rotary friction timer [] are common time delay mechanisms. In the old days, they used a slow-burning fuse.

Which one of these would be easier to build? To me the silly putty seems to be a better option but I can't really find any clear instructions on how to make one.

 

[Roberta314]

Two hints:

-1- Have you seen the movie "The Wrath of Khan"? If so, do you remember Spock's tactical comment to Captain Kirk when Khan was chasing them in the nebula?

Spoiler

-2- There used to be a game called "Mouse Trap" a long time ago (when I was a kid) that had a mechanism that you might be able to use as a basis for your 5-second delay mechanism...

https://i.redd.it/geejcv3e3wl21.jpg

View attachment 253510

Hmm I haven't seen that movie, could you care to elaborate a bit more on that idea for propulsion?

 

[berkeman]

Hmm I haven't seen that movie, could you care to elaborate a bit more on that idea for propulsion?

You go first.

Given my hints, what kind of propulsion mechanisms can you think of? And why would my proposed idea have a good chance of being optimum for the competition?

BTW, I recently helped a team win a competition with minature pinewood derby cars because of something the judges overlooked when setting the rules. The lack of the maximum height of the car in your competition seems like a similar oversight to me.

 

[Roberta314]

You go first.

Given my hints, what kind of propulsion mechanisms can you think of? And why would my proposed idea have a good chance of being optimum for the competition?

BTW, I recently helped a team win a competition with minature pinewood derby cars because of something the judges overlooked when setting the rules. The lack of the maximum height of the car in your competition seems like a similar oversight to me.

So far my idea is to build a catapult using a mouse trap and just attach that onto my car.

And I looked into that scene from "Wrath of Khan" but I can't seem to pick out something from there than relates to my project.

 

[berkeman]

So far my idea is to build a catapult using a mouse trap and just attach that onto my car.

That's certainly a good idea for a starting point. Can you calculate the approximate ratio of the weight of your car to the weight of the mass that you will eject? Why is that ratio important?

And I looked into that scene from "Wrath of Khan" but I can't seem to pick out something from there than relates to my project.

My point was trying to point out that often people don't think in the extra dimensions that are available to them. In the movie scene, Spock was pointing out that Khan was thinking in two dimensions, much as if he was fighting the battle on the surface of an ocean. But in space, there is a 3rd dimension that is available for tactical maneuvers.

And in competitions that eject masses out the back of 2-D cars to see who goes the farthest as a result, there is a 3rd dimension (that you say is not constrained as part of your rules) that is available to supply huge energy storage...

 

[Roberta314]

That's certainly a good idea for a starting point. Can you calculate the approximate ratio of the weight of your car to the weight of the mass that you will eject? Why is that ratio important?

My point was trying to point out that often people don't think in the extra dimensions that are available to them. In the movie scene, Spock was pointing out that Khan was thinking in two dimensions, much as if he was fighting the battle on the surface of an ocean. But in space, there is a 3rd dimension that is available for tactical maneuvers.

And in competitions that eject masses out the back of 2-D cars to see who goes the farthest as a result, there is a 3rd dimension (that you say is not constrained as part of your rules) that is available to supply huge energy storage...

Would increasing the length of the catapult arm(having it launch at at higher spot) allow it to go further?

 

[berkeman]

Would increasing the length of the catapult arm(having it launch at at higher spot) allow it to go further?

Good question. TBH, I don't know and would need to try some example calculations to get a feel for it. Initially on problems like this I think in terms of energy considerations. The stored energy in a catapult would mostly be in the stretched springs, right? The lever arm for throwing the mass using the springs would not affect the stored/transferred energy to a first order, I think.

 

[Roberta314]

Good question. TBH, I don't know and would need to try some example calculations to get a feel for it. Initially on problems like this I think in terms of energy considerations. The stored energy in a catapult would mostly be in the stretched springs, right? The lever arm for throwing the mass using the springs would not affect the stored/transferred energy to a first order, I think.

Since my car only has to travel 6m, I think as long as I have a good wheel and axel design the energy from the just a simple mousetrap catapult should be enough for it to make it that far.

 

[Roberta314]

Good question. TBH, I don't know and would need to try some example calculations to get a feel for it. Initially on problems like this I think in terms of energy considerations. The stored energy in a catapult would mostly be in the stretched springs, right? The lever arm for throwing the mass using the springs would not affect the stored/transferred energy to a first order, I think.

I just built a prototype, although the issue is the mouse trap catapult doesn't seem to be strong enough to propel the car 6m. I am thinking of just buying a bigger mouse trap, but that will for sure increase the weight of the car. So do you have anything suggestions on what else I might be able to do?

 

[Roberta314]