In order for the spring to release all its energy, the spring force must be able to turn the drive wheels throughout the range of motion of the spring, as the car travels on the flat surface. The drive wheel diameter must be as large as possible while allowing the spring to release all its energy.
You have to determine the ideal drive wheel diameter with trial and error. Releasing the spring energy slowly, by way of larger drive wheels, has two key advantages. The second advantage is that the car takes longer to gain speed accelerate which results in it traveling farther than a car that gains speed faster.
However, it is worth mentioning that this equation is an approximation, for two reasons: First, it assumes that there are no friction losses. Secondly, it doesn't account for the rotational motion of the wheels. This equation assumes that the mousetrap car is a fully rigid object. But as it turns out, these assumptions don't change the form of the energy equation and therefore don't affect the validity of my next important point. In the above equation, we see that V is always constant regardless of how fast the car gains speed keeping everything else the same.
It follows that the car travels farther the longer it takes to reach V. After the car reaches V it will coast until it finally stops. But the coasting distance after V is reached will be roughly constant, so the biggest influence on distance traveled on a flat surface is how long it takes the car to gain speed. Use old cds or old records for the wheels and use light, strong wood for the frame.
Attach the mousetrap spring to a big flywheel which has nylon fishing line wound around it. This line from the flywheel is also wound around the drive wheel axle. When the mousetrap spring is released, it turns the flywheel which then turns the drive wheel axle which propels the car forward. You can use low friction bushings for the insertion holes in the frame into which the axles go.
Glue two craft sticks perpendicular to the half-sticks, then apply a generous layer of hot glue over all the sticks and the metal mousetrap arm picture 2.
Glue two more half-sticks on top of the arm as shown picture 3. This sandwiching technique ensures that the mousetrap car arm has a solid foundation and won't bend or break during use. Extend the arm so its three craft sticks long and two craft sticks wide picture 3.
Like the frame, make sure to overlap the sticks by at least 0. Lastly, adjust the length of the arm: add more sticks or cut it shorter until the very end of the arm touches the drive wheel axle. If the arm is shorter or longer than that, then the mousetrap car won't work as efficiently see the step The Science and Math of the Mousetrap Car for more info.
Pull the arm back toward the drive wheels. Apply hot glue to the end and lay the end of the string onto it picture 1. Wrap tape around the string and the arm picture 2. The combination of hot glue, tape, and attaching the string to the underside of the arm will prevent the string from coming undone.
Let the mousetrap arm close it points past the front wheels. Unspool the string from the roll and cut it so it's about " past the drive wheel dowel picture 3. Carefully wind the string around the dowel by turning the drive wheels. As much as possible, try to wrap just one layer of string around the dowel picture 1. Now that you've seen how the car is built, here's an overview of the science and math that's behind the car:. The summary, the science and math concepts behind the mousetrap car manifest as a balance between these principles: lower friction and inertia as much as possible and decrease mechanical advantage as much as possible.
The example mousetrap car built in this Instructable is a good place to start, but it's not the absolute best design. We can use our understanding of the math and science behind the car to test some ways to optimize its performance. The best mousetrap car is one that starts by slowly crawling forward, using the smallest amount of energy possible to get moving. This indicates that it has the lowest possible mechanical advantage.
As the car moves forward, it begins to build momentum. When the arm reaches the end of its arc, the car has generated enough momentum to continue coasting for some distance. The less friction the car generates, the greater the coasting distance will be. With that in mind, challenge your students to think about the following categories of improvement:. If you're planning on teaching this project to a group of kids, then download the attached lesson plan and project sheet. Like all of my lesson plans , it contains the project goal, prep, troubleshooting, and a suggested lesson plan.
The lesson plan is an outline, and it's provided as an editable. This lesson plan also includes all the details on the math and science behind the car. To download the Project Sheet, click on the image and then click on the download button in the lower left corner.
Or, right click and open the image in a new tab, then right click and save the image. I recommend showing how to build the car step-by-step, and then use the project sheet as a reminder of the steps. Print out one project sheet for every 2 students.
Lastly, this project aligns with the following NGSS :. MS-ETS Engineering Design - Develop a model to generate data for iterative testing and modification of a proposed object, tool, or process such that an optimal design can be achieved.
Thanks for reading this far! Forgive me - my first glance to the pic left me wondering "is this designed to trap a mouse? Great design! Will give a try and see how far it can go. This is such a fun STEM activity, but it also covers some important middle school math and science concepts. It's a win-win! Thanks for sharing and including so many awesome resources! Introduction: Mousetrap Car - Explained. More by the author:.
About: I'm a writer, maker, and educator who's on a mission to better the world through hands-on engineering projects. Check out my work: www. Note: the large wheels were removed from this picture for visual clarity, but it's not necessary. The car frame and wheels are complete picture 3! Time to add some mousetrap power. Lift the mousetrap arm and position two half-craft sticks under it as shown picture 1. This project results in a simple mousetrap car.
If one snaps back on your hand it could break a finger. This project requires adult permission and supervision. Cut four wheels out of a piece of foam board or corrugated cardboard adult supervision is necessary. Make the back wheels about double the diameter of the front wheels. Use a compass to draw the circles, or trace around a bowl or cup.
Give your wheels some traction by stretching large rubber bands around each wheel. For the small wheels, you could also try using a section of a balloon. This is the base of the car, known as the chassis. Attach the mousetrap to the chassis, using duct tape. Screw the eye hooks onto the bottom of the cardboard chassis, one in each corner. Use a ruler to make sure that the eye hooks are aligned with each other. Cut the wooden dowel so you have two pieces that are both about two inches longer than the width of the chassis.
These will serve as your axles that rotate the wheels. Stick the dowels through the eye loops. Make sure that the axles are straight and that there is room for them to spin in the eye hooks.
Cut holes a little bit smaller than the dowel through the center of each wheel, then attach the wheels to the chassis. Put the large wheels on the back of the car, opposite the snapper arm.
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