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Physics Experimental Project - A mouse Trap Car How To Make?

This is a mousetrap car.They re common for competitions in high school physics classesJust like the egg drop challenge or building toothpick bridges. The goal is to build a car that travels the furthest or goes theFastest, but in either case the only power provided to move the car is from a single mousetrap. So today I m going to show you how to win first place by building some cars with the World-record holder. Then we re gonna go to the West Coast Championships to see all these principles in action, and wait don t leave! I know that 99.7% of you have never, nor will ever make one of these,but I will break down in simple termshow I know this car will go twice as far as this one,and then I ll prove it. And then we ll discuss why you see these DVD wheels so often, but do they work? And why do some winning cars have wheels that look like this?But before we fly all the way out the Texas to meet the world record holder,I need to lay the foundation for the one overarchingfundamental physics principle behind the mousetrap car.It s called mechanical advantage and to do thatI m gonna need my niece and nephews. "Imma bet you guys I could lift my car off the groundusing just my pinkies. If I can t do it, you can have this crisp Benjaminbut if I can, you guys have to buy me ice cream. Deal?""I said nothing else but your Pinky!I am using just my pinkies.

No just your pinkies." "That s what I m doing!""This is really good you guys. Thank you."If you re willing to move a greater distance.You re able to reduce the amount of force and by a proportional amount.I can t lift 500 pounds worth of car one time.But I could lift 10 pounds 50 times. A mechanical advantage is the ratio of the output force over the input force.So in this case it s 50. That means my hand had to travel 50 times further than just lifting the car in one shot.But the weight was 50 times less, so it was totally worth it. This principle of mechanical advantage is everywhere.Let s take a look at a few examples.If I have 4 pulleys that means I have to pull the rope down 4 times further than the dumbbell goes up.But in exchange, it feels four times lighter, so this has a mechanical advantage of 4. For the rampyou look at the ratio of the length to the height. Your mechanical advantage therefore is 2.2. And that meansI have to travel a little further,But the brick should feel 2.2 times lighterpulling up the ramp versus just pulling the brick straight up. And sure enough if you measure each with a scaleThis is exactly what you see. If you think about it a screw is just a rampwrapped around a nail.

So here you look at this has traveled around the thread and divided by the space in between the threads to get a mechanical advantage of 9 And as you know if you really want to multiply your force use a ratchet wrench Now that is since your hand travels for one full rotation is 300 times longerthan the distance the screw moves vertically between one thread the total mechanical advantage is 300It s like a really long short rampSo if this scale reads 6 pounds the actual clamping force would be300 times more or nearly a tonAnd with wheels and axles it s the same story since this wheel diameter is twice what this one is as you could probably guess bynow this weight weighs twice as much so now we re balanced with a mechanical advantage of 2 And you ll also notice if I move this, the lesser weight travels twice as far and finally we have leversWhich is where we started with my niece and nephews, here if you compare the ratio of the distances from the pivot point we haveA mechanical advantage of 4 which of course means I have to move this end four times furtherBut it s super easy because it s 1/4 the weight on this side, and in all of these examplesWhich you see everywhere around us you trade lower force for more distance travelled.

This is how humans built amazing things before all these fancy machines with engines came aroundHuman muscles are totally strong enough as long as you re willing to spend a little more distance to do the task, and so this principleMechanical advantage is at play over and over again with the mousetrap cars only in reverse. It works both ways in other wordsI don t want the full force of the spring acting over this tiny distance to act directly on the wheels or they would spin outThat would be a very inefficientTransfer of energy from the spring, so we usemechanical advantage and make the main lever arm 15 times longer than the spring lever arm, and then the wheel diameter is24 times bigger than the wheel axle so then if we multiply them our total mechanical advantage is 1 over360. That means the force is 360 times less right here on the output at the wheels to the floorVersus right here on the input on the spring. It also means it will travel360 times further than the distance this spring arm rotatesalright, so that s enough of a foundation for now let s go to Texas and meet up with my buddy Al, to build some racecarsNot only is he the mousetrap car world record holder,but he also kind of started the whole thing, andhe was Texas high school physics teacher of the year, and since my dream job is to one day switch from working as an engineerIn the private sector, to go teach high school physics somewhere.

I made him show me all his cool demos.I came up with this idea back in1991 and since that time I have literally builtthousands and thousands of mousetrap cars myselfI ve seen every possible engineering design you could ever come up withThere s lots of different variations for rules for a mousetrap car race. Let s talk about how to build the bestLong-distance car first for our testing we started with three identical cars the only difference was the length of the lever armSo one was short one was medium, and one was long, and I ve calculated each of their mechanical advantagesWhich you can see written here and given what we know about mechanical advantage. What do you think is about to happen?As you might have guessed the short lever arm car takes a strong early lead this makes sense because it has the largestmechanical advantage therefore the highest forceWhere the wheels and ground meet the downside is that it s a short-lived burst and the medium and long lever arm cars pass it once?

It s quickly used up all its energyIn the end this is how far they eachtraveled with the longest lever arm car going theslowestbut making it all the way to 30 feet this brings up the first principle for the long distance car to win you want thesmallest possible force over the longest possibleDistance in other words the smallest fraction for mechanical advantage possible. You want your car to be barely creeping forwardTo waste as little energy as possibleYou could think of the total energy of the spring as this amount of water in this cup and then this cup representsthe amount of energy that s passed on to your car to move it forward if you just quickly dump it all the energya ton spills and splashes out this will be due to losses from extra heat generated or even drag force from the wind which is proportionalTo your velocity squared, but if you do it slowly and more controlled much more energyGoes to actually moving your car forward the next thing we tested was addingGraphite to the axles on all three of the cars, and then we raced them.

This made a huge difference and now they went this farAgain the longest lever arm car one because it was the slowest but this shows the importance of dealing with frictionIt s definitely your biggest enemy with these cars and the friction comes from two spotsYou have the rolling friction between the wheels and the ground and then the biggie isbetween their axles and the car bodyThis is why we put the lubricating graphite powder there and to take our testing a step furtherwe took the long lever arm car andAdded ball bearings in place of the graphite and that set a new record for us at 50 feet so if you only have onehour to make your carAnd you want to have a good showing you can use a long lever arm like this in conjunction with the CD wheels.

To give you a mechanical advantage of about one over360 and then use ball bearings at the axles or just apply some graphite and you re gonna do pretty wellNext we figured if long lever arms make it travel slower and therefore further. We should do a super long lever armBut it only made it to here which was worse than even the short lever arm car the problem was that it didn t Coast veryWell because we had to make it really big, which means it s more. Heavy, which means more frictionYou know this already intuitively because it s harder to push a heavy object on a table than a light object because there s more frictionResisting you so principle three is to make it lightweightI love this example though because it shows you that you need to balance these principles if you take any one of them too farThen another principle will creep in and start penalizing you. It s an optimization problemAnd that s what makes the mousetrap racers such a great projectThat s also why testing is so important so tweaking and testing different things like Allen and I did iscritical for honing in on the sweet spot for your specific design next we tried this big wheel design which is a popular approach theStrategy here is the wheel is56 times larger than the wheel axle so when you combine it with the lever arm you get a built in mechanical advantage of oneOver 840 and that s the equivalent of a lever armThat s two and a half feet longBut without needing the big heavy car. That seems like a good deal and as such it was our best car yetAnd made it all the way to here. The downside is that it takes energy to get a big wheel like thatrotating it s called rotational inertiaHere s a demo I built to showcase his principle.

These two wheels areidentical except this one has the steel weights placed at the outer edge of the wheelVersus near the axle this means it has a higherRotational inertia so when we spin them both identically the one on the right starts spinning fasterAnd will reach a higher max speed, but the one on the Left will Coast for longer by having biggerHeavy wheels you re basically using them as a temporary storage for your energyAnd then you give it back during the coasting phase the problem with this is anytime you transfer energyYou lose some going back to the cups a little splashes out each time you pour it no matterHow slowly you do it?So instead of pouring your spring energy into a big cup and then eventually getting it back in the coasting phase. It s betterJust to have reasonable size wheels and just have one slow pour directly near the final cup of making your car moveAdditionally big wheels like this can be hard to steer so principle four is to reduce rotational inertia.

This is also why you see people do this to their wheels sometimesIt s an effort to keep the wheels large in diameter to get that built-in mechanical advantageBut to make them wait less to reduce the energy given to rotational inertiaso the final test we ran was Al s world record car which travelled anAstounding 600 feet when he set the record he did some crazy things like using jeweler s bearings on the axlesBut the real secret is this pulley here in the middle if we look at the ratios and calculate the mechanical advantage from the leverTo the pulley to the wheels we re looking at one over four thousand six hundred and eight it s the equivalent of a 16-footLever arm or back wheel four and a half feet in diameterBut without the downside of the extra weight or wasted rotational inertiaThis thing barely crawls along it s hard to even see the spring lever arm moving as this back spinsIt s really hard to beat a design like this.

And now we ll quickly go through the speed car principle since most of the same principles apply the biggest difference is this time we wantTo access all the energy from the spring in a short burst right at the beginningBecause the finish line is only 15 feet awaySo it doesn t make sense to have a really small mechanical advantage like the pulley carHere we want it much closer to the direct force of the spring itselfWhich would be mechanical advantage of one, the problem is if we did that the wheels would slip so you basically want to incrementallyIncrease your mechanical advantage by making your rearaxle thicker and thicker with tape until your rear wheels start to slip slipping is bad of course because that s waste of energy because yourWheel is spinning without actually moving your car forwardIt s helpful to zoom in and use the slow-mo on your phone to see if your wheels are slipping or not this means having goodTraction on your rear wheels is important because means you can have higher forcesBefore you start to slip these squishy foam wheels work greatAnd just like with the distance carReducing friction by using bearings or graphite will definitely help as well making it lightweight because Newton s second law teaches us that heavier things areHarder to accelerate just like you throw a baseball furtherthan a heavy bowling ball andSmaller diameter wheels not only help by keeping your mechanical advantage closer to one but you don t have time to give energy to these bigWheels and then get it back through coasting you want all that spring energy to go directly into making your car go forwardOkay, so those are the basic principles before we head to the west coast mousetrap car championships, I ll just mentionI put a list of 10 practical quick build tips in the video description for exampleYou should soak your bearings inWD-40 to remove all the grease.

The grease is useful if the bearings are actually seeing a lot of loadBut since these cars weigh next to nothingIt s only gonna slow you downI should also mentioned that my buddy Al has an amazing website called or you can buy all the partsI show today to experiment and come up with your own unique design. I also put that link below here we goFor this competition the objective was to travel forward 15 feetAnd then returned back and stopped as close to the exact same spot you started in the least amount of time those moves may seemComplicated but you can switch from forward to reverseby simply switching the direction you wrap up your axle halfway through and you can stop at a certain point by using a wing nutOn a threaded axle so given the rules your design choices should foster both speed and precision about half the designs relied onPreconceived notions and use CD wheels which are a real bad choice here because you re not looking for distanceThey have more rotational inertia and poor tractionThe winning team car which I won t show here because the finals are next month really focused on precision.

They use ball bearings small foam wheels and they made their car body out ofAluminum it weighs more than balsa wood, so it did cost more energy to frictionBut there s plenty of energy in the spring for only traveling thirty feetSo it was worth the trade-off for the extra rigidity and repeatability they also told me they tested and tweaked their design for six monthsIt s just awesome to hang out and see all the various design approachesHopefully you learn enough by now to give you a solid foundation for your own unique designSo you can build, test, tweak like crazy, and then dominate the competitionI spend way too much time making these dumb videosBut I can t help it since I sort of get obsessed because I m passionate about the not only help make this video possibleBut their site is full of people just like me except on any topic imaginableTake graphic designer, Aaron Draplin from Portland, Oregon, for exampleThis guy is a savant who became famous for his amazing logo work and design philosophyHe s a great teacher, and he s hilariousI learned a ton from going through his course. SkillShare is less than $10 a month for their premium membershipAnd that gives you full access to all of their classes and the first thousand people to click the link in the video descriptionGet two months to try it out for $0.99 so if you appreciate the workI put into these videos and you want to learn more from people who are passionate about what they doClick the link below to get started. Thanks for watching.


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