The drive wheels must be small enough so that the spring force can turn the wheels throughout the range of motion of the spring as the car travels up the incline.
This allows the spring to release all its energy without getting "stuck" in some intermediate position. There is no lower limit on how small the drive wheels must be. Simply speaking, they must be small enough for the spring to release all its energy as the car travels up the incline.
This is something that you have to determine by trial and error. The dominant forces on the incline are gravity and the spring force, and by conservation of energy, the vertical distance traveled by the car can be approximated by equating the stored spring energy to the gravitational potential energy gained by the car.
Note that this equation is an approximation because it assumes that there are no friction losses. Interestingly, we see from this equation that the distance traveled up the incline does not depend on the drive wheel diameter. This is true as long as the drive wheels are small enough so that the spring force can turn the wheels throughout the range of motion of the spring as the car travels up the incline.
You can design the mousetrap car so that you have the smaller drive wheels on one end which are suitable for the incline , and the larger drive wheels on the other end which are suitable for the flat surface. And you can easily switch between the two. The figure below shows a basic concept design for the mousetrap car, based on what was talked about here.
The exact type of mechanism needed to transfer the spring energy into forward motion of the car does not matter as long as it enables the spring to release all its energy as the car moves. For example, this mechanism could be a flywheel as described here or a long rod attached to the spring, which turns the axle and the drive wheels.
Or it could be some other type of mechanism. If you decide to use a rod then its center of mass must rise and fall by the same amount as it "swings" through its range of motion. As a result, the net gravitational energy contribution of the rod to the system will be zero. Alternatively, the rod can be cleverly set up so that its center of mass falls by a net amount as it "swings" through its range of motion.
Glue the mousetrap to the frame near the small wheels. Make sure the closed arm is facing toward the small wheels as shown. Mousetraps are not as forceful and dangerous as you might think, especially when the arm is already lowered at least this is true of the Victor brand trap linked in the supplies. They only pose a significant hazard when the arm is pulled back and released quickly, so don't be afraid to get in there and start building!
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. This article will look at how these physics lessons on wheels work, as well as ways you can build your own and maybe even be the "Big Cheese" on your block when it comes to making things that go.
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