# Pinewood Derby® car

One of the most important annual events for Cub Scouts everywhere is the Pinewood Derby®. Each participant starts with the same basic materials – a block of pinewood that is carved into a car shape, steel axles and plastic wheels.

The race track is built according to exact specifications. Cars are placed at the top of the track incline and release to roll down the track. The first car to cross the finish line is the winner of that “heat”. Groups of cars are raced until the winner is determined.

Elements of a fast car

The Pinewood Derby® competitions challenge kids to make the most of the items in the kit. Some cars seem to be much faster than others. Some basic engineering can help determine how to make any car go faster.

• Ask – There are guidelines and restrictions for the cars. There is a maximum weight. How much can a car weigh? What are the maximum dimensions?
• Imagine– Some cars are models of real cars. Some are simple wedge shapes. How air moves over and around the car is important.What shape works best for a gravity car? What shapes work best for real racing cars?
• Plan – Make the car as heavy as possible to maximize momentum. Within the design limits, what is the maximum weight? Where should the extra weights be located?
• Create – The alignment of the wheels is important. How can you be sure the wheels are straight?
• Improve – Adjusting the car to reduce frictional forces can improve speed. These are air resistance, axle friction and tire stickiness. What can you do after the car is built to improve its performance? How can axle friction be reduced?

That’s engineering

• friction – the resistive force that occurs when two surfaces travel along each other when forced together. It causes physical deformation and heat buildup. The frictional force is the force pressing the surfaces together and the coefficient of friction between the materials. The coefficient of friction depends on the materials used — for example, ice on metal has a very low coefficient of friction (they rub together very easily), while rubber on pavement has a very high coefficient of friction (they do not rub together easily). The force of friction is always exerted in a direction that opposes movement.
• lubricant – A common way to reduce friction is by using a lubricant such as oil that is placed between the two surfaces, often dramatically lessening the coefficient of friction.
• graphite – Carbon. Thin flakes are flexible but inelastic, mineral can leave black marks on hands and paper, conducts electricity, and displays superlubricity. Graphite powder is used as a dry lubricant.

Engineering ideas

• gravity, force, aerodynamic drag, inertia, rolling resistance, rotational energy, frictional forces, air resistance, axle friction, tire stickiness

Do it
Here are some challenges for you to work on…

• Already participating? How are you going to improve your own car?
• You don’t have to be a Cub Scout to build and experiment with an actual car. Car kits are available in most hobby and craft stores as well as online. Make one of your own and try out your ideas.