PT2.3 - Construction of Car

Materials:
Wood
String
CDs x4
Cardboard
Electrical tape (for friction and grip)
Tape
Pencils (for lever) x2
Straws x2
Chopsticks x2

The back wheels are wrapped in normal tape to minimise friction between the wheels and the tarmac. The front wheels are wrapped in electrical tape to overcome the inertia of the mousetrap car. Light cardboard was used to make the back wheels to minimise the weight of the car so that it travels a longer distance.

As the mousetrap works using a spring, we decided to transfer the energy from the mousetrap to the axle of the wheels using a string. There would be a lever connected to the hammer to increase the radius of the hammer, and thus, the amount of string that is pulled from the axle. The lever is attached to the string which is wound around the axle. When the mousetrap is released, the lever would make an arc to its original position, uncoiling the string from the axle. The string grips onto the axle, but not too much, and causes the wheels to rotate. The car is thus pushed forward.

Board that holds the mousetrap: We used the wooden board as it is light and easy to cut. It is also sturdy enough to serve as a base for the mousetrap. The surface of the wood is also smooth enough to decrease most of the air resistance and friction.

Hammer: We used pencils to make the lever as they were both long in length and sturdy enough to not be broken by resistance from the string and axles. If the lever is long, it allows for a bigger radius than with just the hammer, so that more string is pulled, making the car travel more distance.

Axles: We used electrical tape to cover up the middle part of the front axle, so that the string would grip on when the mousetrap is released and not simply slide off due to the lack of friction. We also used chopsticks for the axle as they are sturdy enough and their surfaces are smooth enough to spin without much resistance.

Joint of Axle to Board: We used straws for joining the axle to the board as they are the right size to fit the chopsticks, while allowing them to spin efficiently. The surface of the straws are also very smooth, which allows the chopsticks to spin with little effort.

Wheels: Large wheels have greater rotational inertia than small wheels. In practical terms, this means that once they start rolling, they're harder to stop rolling. This makes large wheels perfect for distance-based contests. They'll accelerate less quickly than smaller wheels, but they'll roll much longer and they'll travel a greater distance overall. So, for maximum distance, make the wheels on the drive axle (the one the mousetrap is tied to, which is usually the rear one) very large. (Wikihow, 2016)




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