BACKGROUND:
Students hear about cars that are
aerodynamically designed in many advertisements on television. They
probably have a sense of what it means, because most of these cars are
sleek and low. Cars are designed this way to minimize resistance and
allow them to go faster. The overall design is streamlined which
"cuts" the air. When a vehicle is aerodynamically designed it
can save fuel, because it takes less energy to travel. For race cars and
road cars this is important. However some vehicles do not want to go
faster as much as they need to accomplish a certain goal. For instance,
a farm tractor is not designed to go fast, it is designed to do a job.
The outside of a car is designed to
make use of aerodynamics, but the inside of the car tries to make an
efficient machine that will do work. There are many other laws of
physics in just one vehicle. You may want to go over how a car works
just to illustrate to students that cars are a physical design created
by engineers.
A car is a complex compound machine,
that is fueled by gasoline to create motion. In a car, the engine is
responsible for producing the power that causes the wheels to turn. The
engine turns a rod called a crankshaft which is connected to the drive
shaft which in turn is connected to the axle which of course is
connected to the wheels.
Gasoline is pumped into the gas tank
of the car. From the gas tank, the fuel travels through the fuel line
and reaches either the carburetor or fuel injector. From this point the
gas flow is controlled by the amount of pressure placed on the
accelerator. The fuel is converted into a mist much like a perfume by
the carburetor. This "perfume" is then released into the
cylinders where it is compressed, ignited, and exploded. Each time an
explosion takes place the pistons are forced down, causing the
crankshaft to turn. With each turn of the crankshaft comes a turn of the
drive shaft and with each turn of the drive shaft, comes a turn of the
axle and consequently the wheels.
A car is a complicated and complex
machine that is dependent upon the laws of physics for both efficiency
and performance. Nearly all the laws of physics can be found in the
workings of an automobile. Friction between the rubber tires and asphalt
ground is the reason the car moves (aside from all the workings of the
engine). To better improve friction, tires are built and designed with
tread patterns that grip the asphalt road more efficiently.
Aerodynamics is also a great factor
when it comes to designing cars. Air resistance can contribute greatly
to low gas mileage and poor efficiency. As a result, car manufacturers
design automobiles with pointed fronts, rounded bodies, and streamlined
patterns. With these designs the air can be "cut" so it does
not act like a block stopping the car. A good way to test the notion of
air resistance is to put a hand out of a car when going down the
freeway. A vertical hand pointing straight up will encounter great air
resistance while a horizontal hand will hardly encounter any. This is
the reason cars are pointed in the front and not flat.
Work done by the engine is
transferred to different parts of the car through gears and levers until
this work reaches the axle. Once the work has reached the axle the tires
can be turned and the car can move. For this work to be created,
however, requires the presence of such items as carburetors, pistons,
crankshafts, spark plugs, gasoline, and many other components. A car is
about the best example of all the forces of physics coming together for
one purpose, motion.
PROCEDURE:
- This lab allows students to look
at a model helicopter, airplane, tractor, trucks, and automobile. They
will determine what the design is trying to accomplish. In the previous
labs on design and motion of fluids, students looked at some of the
background reasoning for large vehicles.
- The key objective of this lab is
for students to start realizing that many of the products we use
everyday all had great thought, design, and scientist behind the object.
You can add any other models that you may have so students have a chance
to think about the design. This lab emphasizes aerodynamic design and
not how the inside of the vehicle works.
- You may also want to look at How
Things Work to see how the other vehicles that are used in this lab,
work.
- Part of this lab looks at the
design of balls. Yes, even balls are designed. For this part you might
want to add a football, soccer, and basketball from the gym. Room is
left on the lab sheet for this purpose.
- The answers can vary with your
students. However, they should notice that land vehicles are not as
aerodynamically designed as airborne vehicles. A tractor does not really
care about aerodynamics as much as to accomplish work. A truck is for
more traction and is considered a work vehicle. Large tires on a vehicle
help the vehicles have traction, not to go fast.
- Different balls are designed for
different sports. The football is designed to be thrown, notice the
streamlined shape. The basketball and soccer balls are not
aerodynamically designed but are designed to work well with the hand
(basketball) and foot (soccer). Notice that a golf ball isn't like a
ping pong ball. The little "pimples" are designed to be more
aerodynamic. A ping pong ball would not go too far if hit by a golfer!
