1st place Mousetrap Car Ideas

Summary

This script details the construction and principles behind mousetrap cars, focusing on mechanical advantage to maximize distance or speed. The host, an engineer, collaborates with a world record holder to demonstrate optimal designs, emphasizing the importance of reducing friction, minimizing rotational inertia, and balancing lightweight construction. The video also explores various testing methods and practical tips for building efficient mousetrap cars, ultimately aiming to win competitions.

Takeaways

• 🏎️ The primary objective of a mousetrap car is to travel the furthest or go the fastest using the energy from a single mousetrap.
• 🔧 Mechanical advantage is a fundamental physics principle behind the efficiency of a mousetrap car, allowing for the conversion of less force over a greater distance.
• 🤔 The design of a mousetrap car involves balancing principles such as mechanical advantage, friction reduction, and weight to optimize performance.
• 📏 Longer lever arms in a mousetrap car design can result in a slower but longer distance traveled, due to the increased mechanical advantage.
• ⚖️ Reducing friction is crucial for a mousetrap car's performance, with lubricants like graphite powder applied to axles to minimize it.
• 🔄 Ball bearings can be used to further reduce friction in the axles, contributing to a longer distance traveled by the car.
• 🚫 Large wheels, while providing a built-in mechanical advantage, can be detrimental due to increased rotational inertia and energy loss during coasting.
• 🌀 For speed-focused mousetrap cars, a smaller mechanical advantage is preferred to access the spring's energy in a short burst, avoiding wheel slippage.
• 🏁 In competitions, precision and control are as important as speed, with designs often incorporating mechanisms for switching directions and stopping at specific points.
• 🛠️ Testing and tweaking are essential for refining a mousetrap car's design, as each adjustment can significantly impact the car's performance.
• 🌐 Resources like Al's website, docfizzix.com, offer parts and inspiration for building unique and competitive mousetrap car designs.

Q & A

What is the primary objective of a mousetrap car competition?

The primary objective of a mousetrap car competition is to build a car that travels the furthest or goes the fastest, using the energy from a single mousetrap as the only power source to move the car.

What is mechanical advantage and how does it relate to mousetrap cars?

Mechanical advantage is the ratio of the output force over the input force, which allows for a reduction in the amount of force needed by increasing the distance over which a force is applied. In mousetrap cars, mechanical advantage is used to multiply the force of the spring over a greater distance, making the car travel further or faster.

How does the length of the lever arm affect the performance of a mousetrap car?

The length of the lever arm in a mousetrap car affects its mechanical advantage. A longer lever arm results in a smaller force but allows the car to travel a greater distance, which is beneficial for long-distance races. Conversely, a shorter lever arm provides a larger force but over a shorter distance, which can be advantageous for speed in short races.

Why is friction a significant factor in mousetrap car performance?

Friction is a significant factor in mousetrap car performance because it opposes motion and can waste the energy stored in the spring. Reducing friction by using lubricants like graphite or ball bearings allows more of the spring's energy to be transferred to the car's movement, increasing efficiency and distance.

What is the significance of using CD wheels in mousetrap car designs?

CD wheels are often used in mousetrap car designs because of their low rolling resistance, which can help the car travel further. However, they may not be suitable for all types of races, especially those requiring speed over distance, due to their higher rotational inertia and potential for poor traction.

How does the size of the wheels affect the energy transfer in a mousetrap car?

The size of the wheels in a mousetrap car affects the energy transfer through rotational inertia. Larger wheels can store more energy but require more energy to get them rotating, and they may not coast as effectively due to increased friction. Smaller wheels can allow for a more direct transfer of energy from the spring to the car's movement, but they may not provide the mechanical advantage needed for long-distance travel.

What is the role of ball bearings in enhancing mousetrap car performance?

Ball bearings play a crucial role in reducing friction between the axles and the car body in mousetrap cars. By decreasing this friction, they allow for a more efficient transfer of energy from the spring, which can lead to improved car performance in terms of speed and distance.

Why is the weight of the mousetrap car an important consideration in its design?

The weight of the mousetrap car is important because it affects both the energy required to overcome friction and the car's acceleration. Lighter cars can be accelerated more easily by the spring's force, potentially leading to better performance, while heavier cars may waste more energy on friction and have less energy available for movement.

How does the concept of rotational inertia apply to the wheels of a mousetrap car?

Rotational inertia is the resistance of an object to rotational motion and is related to the mass distribution of the object. In mousetrap cars, wheels with more mass at the outer edge have higher rotational inertia, which can cause them to coast longer but also require more energy to get them spinning. Reducing rotational inertia by using lighter wheels or placing mass closer to the axle can improve the car's performance.

What are some practical tips for building a competitive mousetrap car?

Some practical tips for building a competitive mousetrap car include using long lever arms for distance, applying graphite or using ball bearings to reduce friction, keeping the car lightweight, using small foam wheels for better traction, and testing and tweaking the design to find the optimal balance of mechanical advantage and energy transfer.

Outlines

00:00

🏎️ Introduction to Mousetrap Cars and Mechanical Advantage

The script introduces the concept of mousetrap cars, which are built for competitions in high schools and physics classes. The main goal is to construct a car that can travel the furthest or go the fastest, powered solely by a single mousetrap. The video promises to reveal winning strategies by showcasing the world record holder's techniques and discussing the physics behind these cars. The fundamental physics principle behind the mousetrap car is 'mechanical advantage,' which is explained through various examples, including levers, pulleys, ramps, and screws. The script uses a playful bet with the presenter's niece and nephews to illustrate the concept, demonstrating how moving a greater distance can reduce the amount of force needed, thus providing mechanical advantage.

05:01

🔧 Building the Best Long Distance Mousetrap Car

This paragraph delves into the specifics of building a long-distance mousetrap car. It discusses the importance of the length of the leather arm and its impact on mechanical advantage. Through testing, it's shown that a longer lever arm results in a slower but more efficient car, as it minimizes energy loss. The script emphasizes the need for minimizing friction by using graphite or ball bearings on the axles, as well as the importance of keeping the car lightweight. It also touches on the disadvantages of overly long lever arms and the concept of rotational inertia, explaining why big wheels can be both beneficial and detrimental. The paragraph concludes with a test of a big wheel design and the strategy behind it, highlighting the trade-offs involved in optimizing a mousetrap car's design.

10:02

⚙️ Advanced Techniques for Speed and Precision in Mousetrap Cars

The final paragraph focuses on advanced techniques for building mousetrap cars that prioritize speed and precision, particularly for competitions with specific rules. It discusses the use of pulleys to achieve high mechanical advantage without the drawbacks of weight or rotational inertia, as demonstrated by a world record car. The script also covers the principles for building a speed car, which requires a different approach than a long-distance car, emphasizing the need for quick energy transfer and good traction to prevent wheel slippage. The importance of reducing friction, making the car lightweight, and using smaller diameter wheels for better acceleration is highlighted. The paragraph concludes with a mention of practical build tips and resources for further experimentation, encouraging viewers to build, test, and tweak their designs to achieve success in competitions.

Keywords

💡Mousetrap Car

A mousetrap car is a simple machine powered by a mousetrap mechanism, used in educational settings to teach physics principles. In the video, it's the central theme, with the goal of building a car that can travel the furthest or go the fastest using only the energy from a single mousetrap as its power source.

💡Mechanical Advantage

Mechanical advantage is a physics concept that describes the ratio of output force to input force, allowing for the reduction of force needed to perform work by increasing the distance over which the force is applied. In the video, mechanical advantage is crucial for designing mousetrap cars, as it helps to maximize the distance the car travels with the limited energy from the mousetrap.

💡Lever Arm

A lever arm is the distance from the fulcrum to the point where force is applied on a lever. In the context of the video, the length of the lever arm in a mousetrap car affects its mechanical advantage, with a longer arm resulting in a higher mechanical advantage and a slower, more controlled release of energy from the spring.

💡Friction

Friction is the force that resists the relative motion of two surfaces in contact. In the video, friction is identified as a major factor affecting the performance of mousetrap cars, with reducing friction being key to improving distance and speed by using lubricants like graphite or ball bearings.

💡Rotational Inertia

Rotational inertia is the resistance of an object to rotate or change its rotation rate, which is dependent on the mass distribution relative to the axis of rotation. The video discusses how larger wheels with more mass have higher rotational inertia, which can be a disadvantage in a mousetrap car as it requires more energy to get them rotating and can lead to energy loss during the coasting phase.

💡Pulley System

A pulley system is a mechanical device that supports movement and a change in direction of an applied force. In the video, pulleys are used to create a mechanical advantage in mousetrap cars, allowing for a more controlled and efficient transfer of energy from the spring to the wheels.

💡Ball Bearings

Ball bearings are round, rolling elements that reduce friction between moving parts. In the context of the video, ball bearings are used in mousetrap cars to minimize the friction between the axles and the car body, thereby improving the car's performance by allowing it to travel a greater distance with less energy loss.

💡Graphite

Graphite is a lubricant used to reduce friction. In the video, graphite powder is applied to the axles of mousetrap cars to decrease rolling friction and improve the efficiency of the car's movement.

💡Optimization

Optimization is the process of making design or system decisions that will give the best results under a set of constraints. The video emphasizes that building a mousetrap car is an optimization problem, where balancing principles like mechanical advantage, weight, and friction is crucial for achieving the best performance.

💡Ratchet Wrench

A ratchet wrench is a tool that allows for the application of mechanical advantage by providing a long handle for the user to apply force over a greater distance. In the video, the ratchet wrench is used as an example to illustrate the concept of mechanical advantage, showing how a small input force can result in a large output force.

💡Traction

Traction refers to the grip of a tire or wheel on a surface, which is essential for transferring force to move a vehicle. In the video, having good traction on the rear wheels of a mousetrap car is highlighted as important to prevent slipping and to ensure that the energy from the spring is effectively used to propel the car forward.

Highlights

Building mousetrap cars for competitions involves physics principles like mechanical advantage.

The goal is to build a car that travels the furthest or goes the fastest using only a mousetrap's power.

Mechanical advantage is the ratio of output force to input force, reducing force needed for greater distances.

Examples of mechanical advantage include pulleys, ramps, screws, and wheels and axles.

Mousetrap cars use mechanical advantage in reverse, spreading out the force of the spring over a longer distance.

Longer lever arms on mousetrap cars result in slower but longer travel distances.

Graphite applied to axles reduces friction, increasing car distance.

Ball bearings reduce friction more than graphite, setting new distance records.

Lightweight cars have less friction, allowing for better energy transfer and performance.

Big wheels have higher rotational inertia, which can be both beneficial and detrimental to a car's performance.

Reducing rotational inertia by lightening wheels helps in maintaining speed and energy efficiency.

Al's world record mousetrap car utilized an innovative pulley system for maximum mechanical advantage.

Speed car principles involve accessing all spring energy in a short burst for quick acceleration.

Traction is key for speed cars to prevent wheel slippage and energy waste.

Lightweight design and small diameter wheels are preferable for speed to reduce inertia and increase acceleration.

The West Coast Mousetrap Car Championships require a balance of speed, precision, and design optimization.

Docfizzix.com offers parts and resources for experimenting with and creating unique mousetrap car designs.

Transcripts

- This is a mousetrap car.

(funky music)

They're coming for competitions in high school

physics classes, just like the egg drop challenge

or building toothpick bridges.

The goal is to build a car that travels the furthest

or goes the fastest, but in either case, the only power

provided to move the car is from a single mouse trap.

So today I'm gonna show you how to win first place

by building some cars with the world record holder.

And then we're gonna go to the West Coast championships to

see all these principles in action.

And, 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 terms how

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 to Texas to

meet the world record holder, I need to lay the foundation

for the one overarching fundamental physics principle

behind the mousetrap car.

It's called mechanical advantage.

And to do that, I'm gonna need my niece and nephews.

I'm gonna bet you guys I could lift my car off the ground

using just my pinkies.

If I can't do it, can have this crisp Benjamin,

but if I can you, guys have to grab me ice cream.

All right, deal?

- I said nothing else but your pinkies.

- I am just using 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 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 four pulleys, that means I have to pull the rope

down four times further than the dumbbell goes up.

But in exchange, it feels four times lighter.

So this has a mechanical advantage of four.

For the ramp, you look

at the ratio of the length to the height.

Your mechanical advantage therefore is 2.2.

That means I have to travel a little further

but the brick should feel 2.2 times lighter pulling

up the ramp versus just pulling the brick straight up.

And sure enough, if you measure each with a scale

this is exactly what you see.

If you think about it

a screw is just a ramp wrapped around a nail.

So here you look at this as traveled

around the thread and divide by the space in

between the threads to get a mechanical advantage of nine.

And as you know, if you really wanna multiply your force

use a ratchet wrench.

Now the distance your hand travels

for one full rotation is 300 times longer than the distance

the screw moves vertically between one thread.

The total mechanical advantage is 300.

It's like a really long short ramp.

So if this scale reads six pounds

the actual clamping force would be 300 times more

or nearly a ton.

And with wheels and axles, it's the same story.

Since this wheel diameter is twice what this one is

as you could probably guess by now

this weight weighs twice as much.

So now we're balanced with a mechanical advantage of two.

And you'll also notice if I move this

the lesser weight travels twice as far.

And finally we have levers

which is where we started with my niece and nephews.

Here, if you compare the ratio

of the distances from the pivot point

we have a mechanical advantage of four, which

of course means I have to move this end four times further.

But it's super easy

because it's one fourth the weight on this side.

And in all of these examples, which you see everywhere

around us, you trade lower force for more distance travel.

This is how humans built amazing things

before all these fancy machines with engines came around,

human muscles are totally strong enough as long

as you're willing to spend a little more distance

to do the task.

And so this principle mechanical advantage is at play over

and over again with the mousetrap cars only in reverse.

It works both ways.

In other words, I don't want the full force

of the spring acting over this tiny distance to act directly

on the wheels or they would spin out.

That would be a very inefficient transfer

of energy from the spring.

So we use mechanical advantage

and make the main lever arm 15 times longer

than the spring lever arm.

And then the wheel diameter is 24 times bigger

than the wheel axle.

So then if we multiply them

our total mechanical advantage is one over 360.

That means the force is 360 times less right here

on the output at the wheels to the floor

versus right here on the input on the spring.

It also means we'll travel 360 times further

than the distance this spring arm rotates.

Alright, so that's enough of a foundation for now

let's go to Texas and meet up

with my buddy Al to build some race cars.

(upbeat music)

- [Man] U.S.A.

(upbeat music)

- [Mark] Not only is he the mousetrap car

world record holder

but he also kind of started the whole thing

and he was Texas high school physics teacher of the year.

And since my dream job is to one day switch

from working as an engineer in 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 in 1991 and since

that time I have literally built thousands and thousands

of mousetrap cars myself.

I've seen every possible engineering design

you could ever come up with.

- And there's lots of different variations

for rules for a mousetrap car race.

Let's talk about

how to build the best long distance car first.

For our testing, we started with three identical cars.

The only difference was the length of the leather arm.

So one was short, one was medium, and one was long.

And I've calculated each of their mechanical advantages

which you can see written here.

And given what we know about mechanical advantage

what do you think is about to happen?

- Ready? - Yep.

As you might've guessed, the short lever arm car

takes a strong early lead.

This makes sense because it has the largest mechanical

advantage, therefore the highest force where 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 energy.

In the end,

this is how far they each traveled with the longest lever

arm car going the slowest, but making it all the way

to 30 feet.

This brings up the first principle for the long distance

car, to win you want the smallest possible force

over the longest possible distance.

In other words, the smallest fraction

for mechanical advantage possible.

You want your car to be barely creeping forward to waste

as little energy as possible.

You can think of the total energy of the spring

as this amount of water in this cup, and then

this cup represents the amount of energy that's passed

onto your car to move it forward.

If you just quickly dump in all the energy,

a ton spills and splashes out, this will be due to losses

from extra heat generated or even drag force from the wind

which is proportional to your velocity squared.

But if you do it slowly

and more controlled, much more energy

goes to actually moving your car forward.

The next thing we tested was adding graphite to the axles

on all three of the cars and then we race them.

This made a huge difference

and now they went this far,

again the longest lever arm

car won because it was the slowest.

But this shows the importance of dealing with friction.

It's definitely your biggest enemy

with these cars and the friction comes from two spots.

You have the rolling friction

between the wheels and the ground

and then the biggie is between your axles and the car body.

This is why we put the lubricating graphite powder there.

To take our testing a step further

we took the long lever arm car

and added ball bearings in place at the graphite

and that set a new record for us at 50 feet.

So if you only have one hour to make your car

and you wanna 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 over 360

and then use ball bearings at the axles

or just apply some graphite and you're gonna do pretty well.

Next, we figured if long lever arms make it travel slower

and therefore further, we should do a super long lever arm.

But it only made it to here

which was worse than even the short lever arm car.

The problem was that it didn't coast very well

because we had to make it really big

which means it's more heavy, which means more friction.

You know this already intuitively

because it's harder to push a heavy object

on a table than a light object

because there's more friction resisting you.

So principle three is to make it lightweight.

I love this example though

because it shows you need to balance these principles.

If you take any one

of them too far than another principle will creep

in and start penalizing you.

It's an optimization problem and that's what

makes the mousetrap racers such a great project.

That's also why testing is so important.

So tweaking and testing different things

like Al and I did is critical

for honing in on the sweet spot for your specific design.

Next, we tried this big wheel design

which is a popular approach.

The strategy here is the wheel is 56 times larger

than the wheel axle.

So when you combine it with the lever arm

you get a built-in mechanical advantage of one over 840

and that's the equivalent of a lever arm that's two

and a half feet long, but without needing the big heavy car

that seems like a good deal and as such

it was our best car yet and made it all the way to here.

The downside is

that it takes energy to get a big wheel like that rotating.

It's called rotational inertia.

Here's the demo I built to showcase this principle.

These two wheels are identical

except this one has the steel weights placed

at the outer edge of the wheel versus near the axle.

This means it has a higher rotational inertia.

So when we spin them both identically

the one on the right starts spinning faster

and will reach a higher max speed

but the one on the left will coast for longer.

By having bigger heavy wheels, you're basically using them

as a temporary storage for your energy

and then you give it back during the coasting phase.

The problem with this is anytime you transfer energy

you lose some.

Going back to the cups, a little splashes

out each time you pour it, no matter how 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 better just to have reasonable size wheels

and just have one slow pour directly

into the final cup of making your car move.

Additionally, 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 sometimes.

It's an effort to keep the wheels large

in diameter to get that built-in mechanical advantage

but to make them weigh less to reduce the energy given

to rotational inertia.

So the final test we ran was Al's world record car

which traveled an astounding 600 feet.

When he set the record, he did some crazy things

like using jewelers bearings on the axles

but the real secret is this pulley here in the middle.

If we look at the ratios

and calculate the mechanical advantage

from the lever, to the pulley, to the wheels

we're looking at one over 4,608.

It's the equivalent of a 16 foot lever arm or a back wheel

four and a half feet in diameter, but without the downside

of the extra weight or wasted rotational inertia,

this thing barely crawls along.

It's hard to even see the spring lever arm moving

as this back wheel spins.

It'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 want to

access all the energy from the spring

in a short burst right at the beginning

because the finish line is only 15 feet away.

So it doesn't make sense to have a really small

mechanical advantage like the pulley car.

Here we want it much closer to the direct force

of the spring itself,

which would be mechanical advantage one.

Problem is if we did that, the wheels would slip.

So you basically want to incrementally increase

your mechanical advantage by making your rear axle thicker

and thicker with tape until your rear wheels start to slip.

Slipping is bad of course

because that's wasted energy because your wheel is spinning

without actually moving your car forward.

It'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 good traction

on your rear wheels is important

because it means you can have higher forces

before you start to slip.

These squishy foam wheels work great

and just like with the distance car, reducing friction

by using bearings or graphite will definitely help.

As will making it lightweight

because Newton's second law teaches us

that heavier things are harder to accelerate.

Just like you throw a baseball further

than a heavy bowling ball

and smaller diameter wheels not only help

by keeping your mechanical advantage closer to one

but you don't have time to give energy

to these big wheels and then get it back through coasting.

You want all that spring energy to go directly

into making your car go forward.

Okay, so those are the basic principles.

Before we head

to the West Coast Mousetrap Car Championships

I'll just mention I put a list

of 10 practical quick build tips in the video description.

For example, you should soak your bearings

in WD 40 to remove all the grease.

The grease is useful

if the bearings are actually seeing a lot of load

but since he's cars weigh next to nothing,

it's only gonna slow you down.

I should also mention that my buddy Al has

an amazing website called docfizzix.com

where you can buy all the parts I showed today to experiment

and come up with your own unique design.

I'll also put that link below.

Here we go.

(upbeat music)

- [Man] U.S.A.

(upbeat music)

- For this competition

the objective was to travel forward 15 feet

and then return back and stop as close

to the exact same spot you started

in the least amount of time.

Those moves may seem complicated

but you can switch from forward to reverse

by simply switching the direction you wrap

up your axle halfway through, and you can stop

at a certain point by using a wing nut on a threaded axle.

So given the rules

your design choices should foster both speed and precision.

About half the designs relied on preconceived notions

and use CD wheels, which are a real bad choice here

because you're not looking for distance.

They have more rotational inertia and poor traction.

The winning team car

which I won't show here because the finals are next month

really focused on precision.

They used ball bearings, small foam wheels

and they made their car body out of aluminum.

It weighs more than balls of wood

so it did cost more energy to friction, but there's plenty

of energy in the spring for only traveling 30 feet.

So it was worth the trade

off for the extra rigidity and repeatability.

They also told me they tested

and tweaked their design for six months.

It was awesome to hang out

and see all the various design approaches.

Hopefully you learned enough

by now to give you a solid foundation

for your own unique design so you can build, test, tweak

like crazy and then dominate the competition.

Thanks for watching.

(upbeat music)