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My 8yo son is in the Cub Scouts.

He has a pinewood derby coming up next month and I would like to take this project and turn it into a fun, physics lesson for him.

For those not familiar, a pinewood derby is where you shape a block of wood into a car (or truck, or where ever your imagination leads you) and race it on a track against other cars.

The track looks something like this (not to scale): Pinewood Derby

The black curve represents the track. The peculiar, red triangle with wheels is the car. (Click this link to see the various options for the block of wood.)

So, a few talking points that come to mind are as follows:

  1. Gravity. Obviously w/o this the car would go nowhere when released.
  2. Friction. All wheels come with metal axles. We are allowed to use powered graphite to reduce the friction and make the car move quicker.
  3. Weight. The heaver it is, the faster it will move. However, there is a 5oz max weight the car can reach. Should the weight of the car be evenly distributed to maximize speed?
  4. Design. I imagine the design of the car is important to reduce drag...are there any designs from the previous link you would pick regarding that?

Any thoughts on how to elaborate on the items above?

Is there anything I haven't listed that would be helpful to talk about?

ray023
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  • I've flagged the question for mods attention. It belongs better to physics.SE –  Jan 22 '12 at 20:54
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    This probably belongs better at the physics site. Meanwhile I'll just point out that "The heavier it is, the faster it will move" is wrong, or at least misleading. To a good first approximation, the speed at the end of the initial incline ought to be $\sqrt{2gh}$ independently of mass. What more mass will give you is smaller deceleration resulting from a given amount of drag, and thus better performance on the straight. –  Jan 22 '12 at 21:02
  • Such a experiment is a great idea. 8 year olds don't like to talk theory. You might want to built a few different designs and play with all. Then you have some differences to talk about. Even if you just build a wedge-shaped one, you should run it in both directions - and that leads to your "drag" talking point. For kids, "show first" is the best approach. – MSalters Jan 23 '12 at 09:19

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How far it goes on the flat is a little too random - particularly with the level of engineering in the wheels and bearings on a pinewood derby car. So you might have to explain how a change made the car behave differently than the physics suggests - could be a good way into discussing averages.

At the speeds the car goes at I'm not sure you would easily see the aerodynamic effects of different shaped bodies

What about building a track where the car has to go up a ramp on the other side - you can then notice how it can never get higher than it started and how it gets lower on each cycle and eventually stops.

Martin Beckett
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