# The Car Aerodynamics Quiz

By: Staff

4 Min Quiz

Image: refer to hsw

Fire up the wind tunnel and get ready to answer 30 questions about the many ways air flow affects the performance of cars on highways and speedways. Spoiler alert!

# The term used to define and measure the air resistance acting against a moving car is…

Coefficient of drag is written as Cd in mathematical formulas.

# Imagine a moving car. The area directly in front of the car is an area of…

As the car moves through the air, it compresses and slows the air in front of it, creating an area of higher air pressure.

# What happens when air struggles to fill the void left behind a car that's moving forward?

The pull of the low pressure area behind the car is known as pressure drag.

# What is the term for air molecules that behave in a chaotic manner, moving in multiple directions instead of a consistent flow?

Turbulence usually has a negative effect on a car's aerodynamic qualities.

# What is it called when air molecules break away from the car's surface and become turbulent?

Flow separation, also known as flow detachment, is something to be avoided in aerodynamic designs.

# What is the name for the layer of air molecules that forms along the surfaces of a moving object, such as a car?

Studying the interactions between a car and the boundary layer is one of the most complex aspect of aerodynamics.

# Which part of a car's bodywork helps create an area of low pressure underneath the car?

The front splitter prevents air from flowing under the car, creating an area of low pressure, which helps create downforce.

# What is the optimal cross-sectional shape for suspension components that are exposed to the air (such as in open wheel race cars)?

Oval tubes create the least amount of turbulence and flow separation.

# Along with coefficient of drag, the most important aerodynamic aspect of a car's shape is…

A car with a low coefficient of drag can still have poor aerodynamics due to a large frontal area. For instance, a Sprint Cup car has a lower Cd than an F1 car because the F1's car's open wheels create a lot of drag, but the F1 car is more aerodynamic because of its tiny frontal area.

# The best shape for a car's rear window is…

Any kind of abrupt change in body shape creates flow separation and low pressure/turbulence behind the car, so a gradual slope is best. Examples include the "fastback" window styles found in 60s and 70s muscle cars.

# What helps create an area of high pressure over a car's trunk, negating the low pressure created by the rear window?

A spoiler acts as an air dam, causing air to slow and compress above the trunk. Without it, flow separation would lead to an area of low pressure behind the rear window.

# Does a wing on a race car act the same as a wing on an airplane?

A wing on a car is an inverted airplane wing, curved to create low pressure on the underside of the wing and high pressure on top, which in turn creates downforce.

# Which of these does NOT help create low air pressure underneath a car?

Dropping the front of the car and adding side skirts keeps air pressure under the car low. A ram-air scoop can increase horsepower, but doesn’t affect underbody pressure.

# Why does the trailing car gain speed when "drafting" another car (or truck)?

Drafting works because the trailing car is driving through the hole in the air created by the lead car, so it's not pushing against as much air.

# A wing with an aggressive angle of attack generates both downforce and…

An aggressively angled wing creates downforce (for better grip), but it also generates drag.

# NACA ducts can be used to reduce what?

The specially shaped ducts draw air away from large, flat surface areas where the boundary layer can thicken and create drag.

# What does a rear diffuser do?

A rear diffuser opens up the area under the car, allowing air to flow out from under the car more quickly and smoothly. This reduces the pressure and helps create downforce.

# As a car's velocity doubles, what happens to the amount of drag it experiences?

When a car's velocity doubles, it pushes against the air twice as hard and also encounters twice as much air, so the total drag quadruples.

# What is a potential problem when a race car drafts another car very closely?

Drafting reduces the flow of air to the front of the car, which is the primary means of cooling the engine.