Ideas-InspireScience Fans Embrace the Challenge of Cool DIY Projects

Mousetrap Cars

Latest version of the Quicky Mousetrap using foam block chassis for a summer class entitledldquoEngineering Through Modelsrdquo

Introduction

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Almost everything I know about mousetrap cars I can credit to reading this book from Doc Fizzixrsquos Ihighly recommend purchasing this book and also a mousetrap car kit from Doc Fizzixrsquos Aer buildinga good kit car designing your own will be much easier

Doc Fizzixrsquos Basic Mousetrap Car

Aer building a couple of Doc Fizzixrsquos mousetrap car kits I designed several of my own cars although itwas basically two dierent major designs and then small variations The latest mousetrap car uses afoam block for a chassis coat hanger wire for axles and CD wheels This design works well but it wasdesigned mainly to be inexpensive The Doc Fizzixrsquos mousetrap cars use more expensive materialssuch as brass axles and lever arm which is better

In redesigning this mousetrap car webpage I wanted to introduce more of the educational physicsaspect to mousetrap cars My discussion is by no means completely comprehensive and that is why Isuggest purchasing the Doc Fizzixrsquos mousetrap car book

Phase II in My Website Articles

Balsa version of Quicky Mousetrap Car from

summer class a few years ago

Teachers built Quicky Mousetrap Car at

aer school conference

During the first few years of working with my science related project ideas it was mainly about justgetting the students to successfully build and operate the projects Through workshops I have taughta fairly large number of mousetrap cars of my design have been built I have learned much from thisand have tried to improve on some aspects of my design These mousetrap cars have also been builtwithout my help in all parts of the globe

It is my plan to expand on this and introduce even greater educational aspects that go along with theprojects This will be primarily in the area of physics and math applications I will try to present this ina fun an easy to understand manner In looking at the labs schools are doing with mousetrap cars itappears to be related with recording total distance andor computing the acceleration during the runA background in force and motion will be helpful which will include a discussion of Newtonrsquos Laws

How Does the mousetrap car work

How the mousetrap car functions might appear very simple to people somewhat mechanicallyinclined but many people who see one of my mousetrap cars oen ask ldquohow does this workrdquo Themousetrap car is propelled by the torsional elastic energy from the wound spring of the mousetrapmoving a lever that pulls a string that is wrapped around one axle of the mousetrap car As the leverpulls the string the axle turns as the string unwinds until all the string has been pulled through atwhich point the end of the string that was wrapped around the axle should release and the mousetrapcar should coast for a distance because of kinetic energy until friction causes it to stop

Victor brand of mousetrap on the right is most oen

used in mousetrap cars

Side view diagram of the spring with

lever arm attached

The lever arm which is attached to the mousetrap spring moves through a half circle which 180degrees The torque (amount of twisting force) decreases proportionally as measured farther outfrom the spring along the lever arm

When the lever arm is pulled all the way back the torque will be the greatest That is good because thecar needs the extra force as it starts to move to overcome the opposing force of inertia (Newtonrsquos FirstLaw) This is potential energy with the lever arm pulled back as the mousetrap car moves thisconverts into kinetic energy The force from the wound spring will decrease as the lever movestowards the opposite position from the start

Physics Concepts

Hopefully you have identified that there are many physics concepts in this seemly simple model carLet us outline some concepts that should be studied to understand the operation of the mousetrap

car

Simple machines ndash lever ndash wheel and axle this relates to mechanical advantage

Simple Machine ndash The Lever

Simple Machine ndash Wheel amp Axle

Mechanical advantage is the ratio of output force to input force which is a tradeo between distancemoved and the amount of force Move farther out on input side of the lever and output side movesshorter distance but with more force With the mechanical advantage working in the oppositedirection moving a short distance with more force results in less force in the output but moving a

larger distance In the mousetrap car drive axle the small circumference spun by the string wrappedaround it for a relatively short length propels the much larger drive wheels a much greater distancebut with small amount of force This is why the car must roll with little friction

In the mousetrap car the lever (lever arm) is connected to wheel and axle through a thin line

Newtonrsquos Three Laws of Motion

First Law ndash object at rest will remain at restunless acted on by an unbalanced force Anobject in motion continues in motion with thesame speed and in the same direction unlessacted upon by an unbalanced force Law ofInertia

Second Law ndash states that force is proportionalto acceleration but acceleration is inverselyproportional to mass The formula Force = Massx Acceleration relates to this law and the unit offorce is the Newton

Third Law ndash For every action there is an equaland opposite reaction

Relate This to a Mousetrap Car

First Law ndash mousetrap car is at rest it needs an unbalanced force to start moving any idea where thisforce comes from If there were no friction it would continue to move in the same direction but thefriction is an unbalanced force can you think of sources friction in the mousetrap car

Second Law ndash the force is proportional to acceleration thinking about the formula for torque a _____lever arm would give faster acceleration Acceleration is inversely proportional to the mass Thismeans the heavier the mousetrap car is the acceleration would be ______

Third Law ndash for every action there is an equal and opposite reaction in the mousetrap car the wheelspush down on the floor and the floor pushes up on the _________

Relate This to Real World Example

Check out my blog post Newtonrsquos Laws and the Hybrid Car

Terminology Acceleration ndash most of the mousetrap car lab exercises I have seen deal with total distance andmeasuring acceleration

Acceleration = rate of change in velocity

Velocity = rate an object changes position (vector quantity)

Force = Mass x Acceleration

Note Speed and Velocity are not the same

Speed = rate that an object covers a distance (scalar quantity) Average Speed is just distance dividedby time think miles per hour

The faster the car is accelerating the larger the force but the larger the mass the larger the resistancewill be to the acceleration Think of how a large truck or a train is slower accelerating than anautomobile

Work ndash Power ndash Energy

Work is done when a force acting on an object causes a displacement of the object (it moves)

Power the rate which work is done Power = Work Time standard metric unit of power is the watt Fora long distance mousetrap Low Power is desirable work should be done over long period of time

Energy standard definition is ldquothe ability to do workrdquo this might not be too helpful There are severalforms of energy and oen one form of energy can be converted to another In the mousetrap car thepotential energy in the wound spring (elastic energy) moves the mousetrap car converting to kineticenergy

Constructing the Mousetrap Car

Understanding the physics of the mousetrap car should help in designing a more eicient operatingmousetrap car In building the mousetrap car you need to understand the basic components needed

Chassis ndash frame of the car to which the other components attach to For the mousetrap car it shouldbe rigid yet lightweight The first car I built I used a framework of bamboo which required additionalbracing as the tension of the mousetrap pulling on the string across the length of the chassis wascausing it to twist The next generation of mousetrap cars was built from balsa wood and the currentgeneration use a chassis made from a foam block

In the first prototypes of the bamboo mousetrap

car I noticed that the chassis was twisting from

the force of the lever arm pulling on the rear

axle

Bracing was added to stien the chassis

which solved the problem When the

chassis twisted it caused the car to turn

one direction

Hub ndash this the center of the wheel which attaches to the axle The hub should hold the axle in theexact center of the wheel and the sides of the hub should be exactly 90 degrees to the axle otherwisethe wheel will wobble

I made hubs from cutting squares from rubber tarp

straps and drilling hole through the center

Square hub is glued so as to cover

the hole

Faucet washers can fit in the hole of CDrsquos but I

found the ones purchased through Doc Fizzixrsquos fit

tighter

Faucet washers on Doc Fizzixrsquos

mousetrap car

DOC FIZZIX1728 CDDVD

Shop now

Axle ndash sha is attached to the wheels though the hubs it should be straight as possible or the wheelswill wobble In the mousetrap car one axle acts like a pulley as the string is wrapped around it Thediameter of axle in relation to the diameter of the driving wheels is the mechanical advantage

Wheel ndash mousetrap car rolls on wheels this is the geometric shape of a circle This means you shouldunderstand terms such as diameter circumference radius pi rolling resistance and rotationalinertia I have used CDrsquos clear layers and cottage cheese lids for wheels

Large Wheels ndash using really large diameterdrive wheels gives even larger mechanicaladvantage for greater distance

Bearing ndash this is the contactpoint between the turning axleand the attachment to thechassis the less friction in thebearings the more eicient themousetrap car With too muchfriction in the bearings themousetrap the mousetrapmight not even move or stoprepeatedly

Lever Arm

The lever arm extends from the mousetrapspring as a lever to pull the string Threemajor considerations for the lever arm

Material it should be very sti but light inweight Attaching to the mousetrap spring thereis a great deal of force where the lever armis attached to the spring The length of the lever arm is importantthe longer the arm the more line can bepulled through and mousetrap car shouldgo farther

The lever arm on this car is made from a square stock of a hard wood originally I started withbalsa with a T-joint but students were breaking the balsa Aer handling delicate balsa structures inmodel airplanes it was not a problem for me

Torque and Lever Arm Calculations for a Mousetrap Car

Torque has been defined either as a twisting force or the tendency to rotate around an axis Acommon example of torque is tightening a bolt with a wrench To know how much torque is beingapplied to a bolt a mechanics will oen use a special type of wrench known as a ldquotorque wrenchrdquo so aspecified amount of torque can be applied to a bolt

The formula for torque is very simple if the force is applied perpendicular to the lever Torque =radius x force Normally units of torque are foot pounds or newton meters This equation gives thetorque applied to the pivot point this is the mechanical advantage concept

I have been thinking more about how math could be used to predict an outcome To start with amousetrap car if you could calculate what force is available at the end of the lever arm based on thetorque at the axis it would give you some idea on how much force is available to propel the mousetrapcar It is also interesting to see how the force decreases as the spring unwinds

For a mousetrap car that will go a long distance the lever arm needs to be longer to pull more line thatis wrapped around the driving axle From these calculations it can be easily seen that the amount offorce available rapidly diminishes as the length of the lever arm increases

To me it is also interesting if you can measure calculated outcomes and think about the reasons forinaccuracies For this experiment inaccuracy was related to the spring scale I was using and how I wasusing it Doc Fizzix sells a torsion wheel to measure the torque of the mousetrap spring Link toTorsion Wheel product

The lever arm on this car is made from a square stock of a hard wood originally I started withbalsa with a T-joint but students were breaking the balsa Aer handling delicate balsa structures inmodel airplanes it was not a problem for me

Torque and Lever Arm Calculations for a Mousetrap Car

Torque has been defined either as a twisting force or the tendency to rotate around an axis Acommon example of torque is tightening a bolt with a wrench To know how much torque is beingapplied to a bolt a mechanics will oen use a special type of wrench known as a ldquotorque wrenchrdquo so aspecified amount of torque can be applied to a bolt

The formula for torque is very simple if the force is applied perpendicular to the lever Torque =radius x force Normally units of torque are foot pounds or newton meters This equation gives thetorque applied to the pivot point this is the mechanical advantage concept

I have been thinking more about how math could be used to predict an outcome To start with amousetrap car if you could calculate what force is available at the end of the lever arm based on thetorque at the axis it would give you some idea on how much force is available to propel the mousetrapcar It is also interesting to see how the force decreases as the spring unwinds

For a mousetrap car that will go a long distance the lever arm needs to be longer to pull more line thatis wrapped around the driving axle From these calculations it can be easily seen that the amount offorce available rapidly diminishes as the length of the lever arm increases

To me it is also interesting if you can measure calculated outcomes and think about the reasons forinaccuracies For this experiment inaccuracy was related to the spring scale I was using and how I wasusing it Doc Fizzix sells a torsion wheel to measure the torque of the mousetrap spring Link toTorsion Wheel product

For my experiment I measured the force in grams at 4 centimeters from the axis at 25 90 and 180degrees I then measured at 28 centimeters from the axis and then calculated what the force shouldbe based on the measurements at 4 centimeters Measurements were also taken at 28 centimeters soa comparison could be done between the calculated and the measured Fairly close results

GFCM is the torque dividing by the radius gives the force Example 1600 28 = 5714 3200 28 =11429 and 4400 28 = 15714

Above are the comparisons of the measurements and the calculations which appear in red

Measured Forces on Lever Arm at 25 Degrees

Measured Forces on Lever Arm at 90 Degrees

Measured Forces on Lever Arm at 180 Degrees

The concept of torque is also important in flight like in this quadcopter checkout my article Basic Quadcopters

Notes on Units

Many times formulas are based on units other than those you have collected your data with Myspring scale does display Newtons also but grams are a much smaller unit which helps in taking moreaccurate measurement

For Example to Compute the Potential Energy of Torsional Spring conversion to Newtons metersand radians are needed

1 gram = 0098 Newtons

Radians = (degrees π) 180

1 centimeter = 01 meters

1 joule = force of 1 Newton through a distance of 1 meter

Blog Article 10-10-2017 Mousetrap Car Demonstration at Nursing Home

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60 thoughts on ldquoMousetrap Carsrdquo

56

adidas f50adizeromessi

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April 29 2014 at 232 pm

Anonymous

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January 20 2015 at 1141 am

Jam2033

It was pretty good

May 4 2017 at 111 am

Anonymous

Excellent source of student language information Great project for my 5th gradestudents Excellent job

May 12 2014 at 930 am

DFB trikot2014

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May 30 2014 at 509 pm

snazzynazzy

I LOVE THIS WEBSITE I USED IT FOR MY PRIMARY CLASSES

August 14 2014 at 856 pm

Wolf

What is a primary class -Wolf

September 11 2014 at 457 pm

Wolf

Thanks for this info sadly for our project we canrsquot use kits But what do yourecommend for the axles I have been having trouble with them -Wolf

September 11 2014 at 456 pm

Bill Kuhl

If you look at my design for mousetrap car I used coat hanger wire try to findstraight sections Better kits use brass tubing Then you need a hub on mydesign I cut sections of rubber tarp strap and drilled a hole in it For bearing Iused the metal screw eyes

September 11 2014 at 509 pm

hi

very goo I got our mouse trap car idea from this website thanks mr miller these aregreat ideas

September 18 2014 at 344 pm

Anonymous

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October 16 2014 at 242 pm

Anonymous

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December 12 2014 at 1027 am

allie

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December 12 2014 at 1027 am

liv

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March 30 2015 at 1240 pm

Anonymous

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January 13 2015 at 252 pm

Anonymous

Its helpful because even when ur building one in science

January 14 2015 at 1012 am

Nobody

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March 6 2015 at 1055 am

Anonymous

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March 30 2015 at 943 am

Damian

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March 30 2015 at 948 am

Anonymous

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May 8 2015 at 1111 am

Bod

l love it so much i mad 24 cars i love the experiences it is life changing

May 8 2015 at 1113 am

May 11 2015 at 909 am

Anonymous

Its helpful because even when ur building one in science

January 14 2015 at 1012 am

Nobody

SO AWESOME

March 6 2015 at 1055 am

Anonymous

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March 30 2015 at 943 am

Damian

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March 30 2015 at 948 am

Anonymous

great i love it

May 8 2015 at 1111 am

Bod

l love it so much i mad 24 cars i love the experiences it is life changing

May 8 2015 at 1113 am

May 11 2015 at 909 am

Anonymous

cool

Jenna

Excuse me I love your work but could you please tell me when you published thisarticle Thank you

August 31 2015 at 500 pm

Bill Kuhl

This webpage on mousetrap cars was redone last year I had a somewhat dierentwebpage for several years

August 31 2015 at 923 pm

Crush

How do you true the wheels axels and attach-point on the chassis Despite all myeorts the wheels and chassis still have wobble to them and the car doesnrsquot drivein a straight line I found it very diicult to get everything centered and aligned onall axis

October 13 2015 at 1145 pm

Bill Kuhl

Crush that was a good question Wheel wobble has to to do with how straight andsolid the hub axle joint is You need to make sure the wheel to the axle isperpendicular that is like a ldquoTrdquo The axle alignment with the chassis of the car hasto be that way also Some method of adjusting the steering and then setting it maybe desirable On my design I used the screw eyes in a way small adjustments couldbe done on the tracking Some Doc Fizzix cars pivot the front axle and then allowyou to tighten it down

October 14 2015 at 811 am

very helpful got an A on my project and im in 7th grade

October 19 2015 at 156 pm

a 7th gradernamedjacob

Bill Kuhl

Thank you Jacob in 7th grade it makes my eort seem worthwhile

October 19 2015 at 223 pm

Michel

Over-tightening could be in the same way harmful because under-tighteningExamples include motors as well as equipment assemblies

November 15 2015 at 207 am

KilenTora

This was a great help for me in science or I probably would of failed science Verydescriptive and easy to understand as well Thank you

January 4 2016 at 945 pm

JeerySmogelton

This is the best website I have ever seen OMG

February 1 2016 at 1032 am

Bill Kuhl

Mousetrap McGee somehow I doubt you are building a mousetrap car every 4hours but I canrsquot stop laughing reading your comment

February 12 2016 at 823 am

Do yuo doubt me I got over 700 hundred and countingg I typing with onehand becuase Irsquom making mousetrap cars with the other Irsquom beginnning to

March 4 2016 at 814 am

MousetrapMcGee

think I hava problem Please help me bill your my only hope 0

Halal

i like your thinking

-wolf

April 11 2016 at 610 pm

MousetrapMcGee

I used to not know how to make a mousetrap car This article has changes my lifeNow I make a mousetrap car every 4 hours This article has brought meaning to mylife Great Googly Moogly I never realized how awe-inspiring mousetrap cars canbe Golly Josh Darn it why didnrsquot I find this page before Now my warehouse hasapproximately 352 mousetrap cars and counting 0

February 12 2016 at 813 am

Ken M

These mousetrap cars have ruined my life I worked with my son to make one andhe proceeded to show his friends Now the whole neighborhood is littered withthese things I have gotten several complaints and even threatened with a lawsuitfrom my neighbors for harassment and assault from the injuries inquired from themouse trap Every morning I wake and slip on a mousetrap car down the stairs Ihave been to the hospital three times and my wife threatens to leave me Lastweekend a mousetrap car took my job and I am on the verge of losing my homeWhy hasnrsquot Obama stepped in to clean this mess up The federal government failsitrsquos citizens once again

March 9 2016 at 1050 am

Fat Fart

Yoursquore a legend

April 4 2016 at 1053 am

September 21 2017 at 1059 am

NoybNoybie

im screaming is this real

Alex

Irsquom planning to use this idea for a summer camp If I have the kids from 9am to4pm is this a 1 day project Or multi-days

March 19 2016 at 925 am

Bill Kuhl

I have been doing it within one 1 12 hour class This didnrsquot give much time torun the cars

March 19 2016 at 319 pm

me

this is good

March 31 2016 at 812 am

a person

this site was helpful

April 20 2016 at 731 am

Anonymous

legendary

April 22 2016 at 1112 am

May 3 2016 at 1230 pm

oicial_lover_of_mousetrap_cars

I made 500000 mousetrap cars and counting I have been making them since lastyear and I absolutely love them I have caught around 100000 mice from my houseand garage in total

hunter

100000 you say Seems quite excessive donrsquot you think

September 7 2017 at 1117 am

Eliza

May 10 2016 at 1227 pm

Cammie

Thatrsquos not just logic Thatrsquos really senbesli

July 17 2016 at 935 pm

Anonymous

very helpful thanks

July 20 2016 at 802 pm

Gerald

very helpful thank you for your help

July 20 2016 at 803 pm

oicial_lover_of_mousetrap_cars

I made 500000 mousetrap cars and counting I have been making them since lastyear and I absolutely love them I have caught around 100000 mice from my houseand garage in total

hunter

100000 you say Seems quite excessive donrsquot you think

September 7 2017 at 1117 am

Eliza

May 10 2016 at 1227 pm

Cammie

Thatrsquos not just logic Thatrsquos really senbesli

July 17 2016 at 935 pm

Anonymous

very helpful thanks

July 20 2016 at 802 pm

Gerald

very helpful thank you for your help

July 20 2016 at 803 pm

Sarah

Thank you I am trying to reference this site can you tell me the date this page wascreated

August 25 2016 at 745 pm

Bill Kuhl

From the editor I see Published on Dec 13 2013 1136

Bill Kuhl

August 26 2016 at 1237 pm

Pingback 31Aug ndash Term1 Day18 ndash cvintroengcar

Anonomus

Realy helpful best site there is 3

October 24 2016 at 744 am

A BoardIndividual

The only truly good website for mousetrap cars there is good for science fairprojects 3

December 20 2016 at 650 am

Anonymous

OMG best website ever thank you lt3

March 28 2017 at 339 pm

OMG best website ever thank you lt3

March 28 2017 at 341 pm

minimuinninja

Lyn

Good article

June 8 2017 at 1248 pm

Mico

Hello there Maybe you could help me solve a problem on mousetrap car Do youhave any idea on how to turn the wheel of a mousetrap car The problem is weneed to avoid an obstacle 1 meter away and should get back to the line of distancefrom where my car starts The longest distance the car traveled from the obstacle isthe winner The vehicle must start from behind a start-line and then clear anobstacle as it travels the longest possible distance in the longitudinal directionfrom the start line The device must come to a rest as close as possible to a pointdirectly inline from its start location (ie minimise the transverse distance)

August 21 2017 at 404 am

Bill Kuhl

There was a rubber powered event that had to go around an obstacle but youcould make the steering adjustable to a fixed setting and then curve around theobstacle As far as stopping at a certain point there is a Doc Fizzix car like thatwhich uses a threaded rod and a wingnut One side of the wingnut goes in achannel You adjust where wingnut starts and when it gets to one side it stopsthe car

August 21 2017 at 940 am

Mamcee

-This Is Epic I Got Everything I Needed hellip THANK Yu

September 16 2017 at 1129 am