Science Buddies: "Ask an Expert"

Dear all Experts,

In My experiment I am testing different body types made of balsa wood. They vary from streamline to blunt. I have a question on how drag affects a car and what is fluid friction and how it relates to my project. It would be great if you could answer a couple of my questions! Thank You =0.

Dear katzb,

We'll do our best. What are your questions?

In your post, there wee three questions:

1. how does drag affect a car?
2. what is fluid friction?
3. how does fluid friction relate to my project?

Are these correct? Do you have other questions?

Note, you may try inputing the three questions above to answers.com, noting that you may need to change question #3 to have different text for "my project".

I would like to interview an expert because it is a requirement for a science project it will only be 5 questions. thank you for your help!

Hi Katzb,
I merged your new topic with your old one so that the experts can see the history of your project and questions. Please keep future posts for your project in this topic. If you would like to post several interview questions related to your science fair project, please feel free.
Good luck!
Chris

Sorry, I only need 3 questions asked not 5. Sorry for the false information. These are the three that would like answered. If you could do this I would appreciate it greatly! Thank You
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1. How does drag effect a car?
2. What is fluid friction?
3. How does Aerodynamics effect a car?

Hi katzb,

As I mentioned earlier, the my first approach is to take the questions and use them as input to answers.com. If the output doesn't give an good answer, the question may need to be changed. Usually, however, a change is not required.

Why don't you try doing the above, and letting us know how it all works out.

Hi --

A pretty clear explanation of drag and how it's caused can be found on wikipedia:

http://en.wikipedia.org/wiki/Drag_(physics)

Your three questions are good ones and I think you'll be able to get the answers, and also
get a better appreciation of fluid physics, by reading the article. Try answering the three
questions, based on what you read, and post your replies to the group. Good luck!

Peter Young

Fluid friction refers to the paralell force between two bodies, one of them usually being a fluid.
In regards to the aerodynamics of a car, fluid friction is very important.
That's because air can be considered a "fluid" and as a car is accelerating, there is a force between the air and the car's surface.

Another way of looking at fluid friction is a car on a slippery road. You're probably fully aware that drivers should be extra careful when the roads are wet from the rain or snow. This is because there is less friction between the tires and the roads. The physical equation that demonstrates this idea is
coefficient of friction x Normal Force = Frictional Force
http://www.school-for-champions.com/sci ... uation.htm (to see the equation and more info)

The coefficient of friction is a unitless number that shows how much friction a certain material can have when in contact with other surfaces.
When it rains/snows, the coefficient of friction of the roads decrease. As a result, there is less frictional force and the roads are more dangerous.

Hope that helps!

Can anyone help me out? I keep getting the world's biggest words in research. Can anyone summarize Aerodynamics

Aerodynamics is the study of how air (and to a lesser extent, other gases) interact with things. Air can push on things if it's moving and it can resist things that try to move through it. The two main things that aerodynamics study are lift, which is how the shape of a thing can cause air to lift it against gravity and drag, which is how air can slow something down (working against it) that's trying to move through it. Lift is good for airplanes, and bad for race cars. Drag is good for parachutes and bad for airplanes trying to go fast.

Howard

Aerodynamics, or more accurately "the aerodynamic characteristics of a car", affect it primarily in 3 ways.


1. Drag - as described above. A car which has more difficulty pushing through air because of its shape will need more power to go the same speed. This means drag affects both top speed and fuel economy, the former more important for a racing car, the latter for the kind of car most of us drive.
2. Stability - As you push through the air, that air is shunted to the side and roof of the car. Exactly what happens as a result of this can vary quite a bit - a car designed to travel 100mph on a curving road will use that air to push down on the suspension and tires, making it "stick to the road" - the reverse of how a wing provides lift to an airplane. Most cars will hit points where they vibrate or feel unsafe to the driver if you go faster than they're designed, or in conditions unexpected to the designer. You can't really make a car that has good aerodynamics for stability at all speeds, most cars have a "sweet spot" in speed where their aerodynamics are best suited for the airflow. A high performance car will actually perform better at 100mph than 50mph, where a typical consumer car is designed to have good characteristics in a range of speeds around 60mph, the legal speed limit in most areas.
3. Cross-wind behavior - if you drive a SUV or Van, it will often be hard to control in a high-winds situation, where the wind is in a direction other than straight ahead. By contrast, a sports car that is low to the ground (a good profile for #2, stability, in many cases), will be far less affected. This is also an aerodynamic effect, but one where the airflow over the car is not caused by the motion of the car, but instead the wind direction relative to the car.

A car designer has to consider all three of these factors when choosing the shape for a new car. In addition, you have to consider that all of the stuff inside the car has to fit in that space, and that some shapes will require more materials to make than others to accomplish that goal. Finally a car designer has to also consider the appearance of the vehicle. It can have the best aerodynamics in the world, and be efficient in containing the car at a low cost of materials but that won't matter if nobody buys the car because it looks strange or ugly.