Powered by the Wind: A School Project Car

In summary, the car is able to move forward because the momentum of the wind is greater than the drag.
  • #1
ponjavic
225
0
Ok I have built this car for a school project that is supposed to go against the wind. As there is a wind it should be able to drive into it (powered by the wind).

Now the car is built and it is working. I have mounted a horizontal windmill that through gearing powers the back wheels.

What I wonder is, why is the the torque, or for constant velocity the angular momentum, greater than the drag on the car?
 
Physics news on Phys.org
  • #2
ponjavic said:
Ok I have built this car for a school project that is supposed to go against the wind. As there is a wind it should be able to drive into it (powered by the wind).

Now the car is built and it is working. I have mounted a horizontal windmill that through gearing powers the back wheels.

What I wonder is, why is the the torque, or for constant velocity the angular momentum, greater than the drag on the car?
Interesting question. In fact, it is a great question.

Since forces act in equal and opposite pairs, one might think that the force of the wind against the car could not be less than the force of the car against the wind. One can think of an analogy of someone firing cannonballs at the car and the car capturing those canonballs to move toward the cannonballs. It seems to defy conservation of momentum.

The answer has to do with the difference between energy and momentum. The car is driven by wind energy, not its momentum.

Let's look at my example of the cannonballs. Imagine that the car captures the cannonball with a pocket mounted at the end of a horizontal arm. This causes the arm to spin around (like your windmill) converting the cannonball's kinetic energy into rotational kinetic energy. Linear momentum of the cannonball is transferred to the car and the car experiences an impulse to the rear (ie. in the direction of the original cannonball). This can never be avoided. But if the cannonball has a mass that is 1/100th of the mass of the car, the rearward speed of the car due to the cannonball impulse is 1/100th of the speed of the cannonball. So, and this is the critical issue: the car's rearward kinetic energy due to its capture of the canonball is [itex]1/2mv^2[/itex] so it is 100 x 1/10,000th or 1/100th of the energy of the cannonball. Since the rest of the cannonball energy has been stored in the rotating arm, the car can use this energy to move forward. And it does.

Think of the wind as continuous cannonballs. There are other factors, of course, such as wind resistance. But these depend on the design of the car and can be managed.

AM
 
  • #3
Sweet comparison, yeah a constant flow of cannonballs would also hit the car itself but off course the pockets were the main issue.
thank you very much!
 

1. How does the wind power the car?

The car is powered by a small wind turbine attached to the top of the car. As the wind blows, it rotates the turbine, which generates electricity to power the car's motor.

2. What materials are used to build the car?

The car is built using lightweight and durable materials such as carbon fiber, aluminum, and high-density foam. These materials are able to withstand the forces of wind and movement while keeping the car light enough to be powered by the wind.

3. How fast can the car go?

The speed of the car depends on the strength of the wind and the design of the car. On average, a wind-powered car can reach speeds of 20-30 miles per hour. However, some advanced designs have been able to reach speeds of up to 50 miles per hour.

4. Is the car safe to drive?

Yes, the car is designed with safety in mind. It is built to be aerodynamic and stable, even in strong winds. The materials used are also tested for durability and strength to ensure the safety of the driver and passengers.

5. Can I build a wind-powered car at home?

Yes, it is possible to build a wind-powered car at home with the right materials and tools. However, it is important to have a good understanding of aerodynamics and engineering principles to ensure the car is safe and efficient. It is also recommended to work with an experienced mentor or join a school project team to learn and build a wind-powered car.

Similar threads

  • Introductory Physics Homework Help
Replies
4
Views
775
  • Introductory Physics Homework Help
Replies
19
Views
1K
  • Introductory Physics Homework Help
Replies
13
Views
2K
  • Introductory Physics Homework Help
Replies
3
Views
2K
  • Mechanical Engineering
Replies
26
Views
11K
  • Introductory Physics Homework Help
Replies
8
Views
2K
Replies
69
Views
10K
  • Introductory Physics Homework Help
Replies
7
Views
1K
  • Classical Physics
3
Replies
95
Views
4K
  • Introductory Physics Homework Help
Replies
8
Views
2K
Back
Top