In addition to the minimum distance, the car will continue to travel due to momentum. This extra distance depends on several factors such as the car weight, the surface it's driving on, and the amount of friction at the axles, which are too varied to reliably calculate here.
When I tested the car at a tennis court, this calculation proved to be fairly accurate. The car traveled the width of a standard tennis court plus a few additional feed under the power of the mousetrap, then coasted for a few more feet for a total travel distance of about 44ft!
In theory, this would make the drive wheels will turn more times, and the car will drive farther. However, longer string also necessitates a longer arm and frame, which adds further weight. If the frame is shorter than the string, then part of the string won't be able to wrap around the drive wheels. This defeats the purpose of elongating the string: the total usable length of the string is equal to the diameter of the arm arc, so any string that's not wound around the drive wheels is essentially wasted.
The added weight generates more friction , which mostly occurs at the point of contact between the straws and the dowels. This means that making the string longer is only helpful to a certain point! It's possible to create a car that's too long and heavy. Therefore, the sring needs to be long enough to create very low mechanical advantage, but if it gets too long then it'll necessitate a car that's too heavy and slow.
Wheel size Large wheels will also theoretically result in greater distance since the a larger circumference will increase the minimum distance travelled Remember the formula is drive wheel circumference x number of times the string is wrapped around the dowel.
However, just like adding a longer arm, larger wheels can be heavier, but this is problematic for a different reason. Larger wheels don't generate friction in the same way as a larger arm; the wheels do not weigh further on the axle. Larger wheels still create more friction between the edge of the wheel and the surface it's rolling on.
Heavier wheels press into the ground with more force, which increases friction. Additionally, large wheels have more inertia , which is the tendency for objects to remain at rest. This means it requires more energy to move larger wheels. Furthermore, whenever energy is transferred from one source to another, some of it is lost.
This means that the larger wheels cannot store that extra energy very efficiently in the form of momentum. With that in mind, challenge your students to think about the following categories of improvement: Weight The first and most straightforward optimization is to make the car lighter.
A lighter car will generate less friction, which means the car will coast farther using its momentum. What materials can be removed and the car will still work? Are there lighter materials that could be substituted for the heavier ones? Friction The biggest enemy of a high performing mousetrap car is friction. There are ways to reduce friction without removing weight. First, look for any imperfections that might create excessive friction, such as bits of hot glue inside the straws, or the wheels pressed too tightly against the ends of the straws.
Cleaning up small things can have a big impact on performance. From there, what else could you do to reduce friction? How could you modify the design so the side of the wheels doesn't rub against the ends of the straws? How can you reduce the amount of contact between the front wheel dowel and the straw? String Length The length of the string and consequently, the length of the extended arm and frame plays an important role in determining how many times the drive wheels will rotate under the power of the mousetrap, but making it too long will increase the weight and consequent friction.
Making the string too long may also create an extremely low mechanical advantage. If the mechanical advantage is too low, then the output force will be too weak to overcome the car's inertia. How long can the arm be before it becomes too long? Drive Wheel Dowel Another way of lowering the mechanical advantage is to change the drive wheel dowel thickness. So for example, in theory, replacing the 0.
However in practice this won't work so well. The thin dowel may bend under the strain of the force of the mousetrap, causing excessive friction or even preventing the car from moving at all. Additionally, this equation assumes that the string will be wrapped in a single even layer over the dowel, but there isn't enough space for that; the string will start to wrap around itself, which increases the diameter of the dowel, and therefore results in a fewer number of wraps.
What's the ideal dowel thickness? What other string-like materials can be used that can be wrapped around the dowel more efficiently? 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.
Attachments Mousetrap Car. Did you make this project? Share it with us! I Made It! A Literal Handbag by Tatterhood in Halloween.
Chameleon Mask by hugheswho in Halloween. But smaller drive wheels are better for going up an incline. 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.
You power it by simply setting the trap and let it loose by springing the trap. Lots of variations of mousetrap-powered cars have, ahem, sprung up: People have built designs with two, three and four wheels, and out of a variety of materials. Builders have reported achieving distances of close more than feet If you're looking for a neat school project, an activity that's more hands-on than video games or a way to put those old Victor-brand traps to work on a peaceful purpose, try building a mousetrap-powered car!
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. Sign up for our Newsletter!
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