Science Blog from scienceofeverydaylife.discoveryeducation.com
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Introduction
After finishing the turkey for
Thanksgiving dinner, I was able to partake in another Thanksgiving Day
tradition: watching football. I
played football through my high school years, and I coached high school
football during my teaching career
. I absolutely love
the game!
When coming up with ideas for this
blog, there is no more obvious place for me to look for physics
to appear than on a
football field. Gravity
, mass, weight, and motion all play a vital role in the game.
There are 300-pound linemen tackling 180-pound running backs, kicking, running,
punting and throwing. All of these actions are carefully orchestrated within
the laws of physics.
As a kid, one of the first things I was
taught about football was how to throw it. Placing your fingers on the ball, the proper
release, and the proper angle to release the ball at: all of this leads to being able to throw a
perfect spiral. Why a spiral? Why not throw the ball end-over-end? The obvious answer is because it is easier to
catch that way, but is there another
reason?
The Principles
There are a few concepts we need to
address in order to answer this question.
- Forces
- Newton 's Laws of Motion
- Friction (Aerodynamics)
Simplified, a force is a push or a pull
on an object. In order for an object
to move (or stop moving), a
force must first be applied
(see Newton
's Law's below). Objects do not move (or stop moving) just because a
force is applied to them, either.
Forces can be added and subtracted. If
two forces are working in the same direction, they are added together. An
example of this occurs during a car accident when a car rear-ends another. The force of the car from behind is added
to the force of the car that gets hit.
If two forces are working in opposite directions of each other,
they are subtracted. An example of this occurs when you sit in a
chair. Gravity
is pulling you
downward, and the chair is pushing you upward. These forces are equal (they
cancel each other out), so there is no
motion.
When throwing a football, the
quarterback certainly must apply
a force to the
football in order to get it to his
receiver, but are there any other forces at work on the football? The answer is yes — the two biggest forces being gravity and wind resistance
(a frictional force often called
drag).
Gravity causes the ball to fall towards
the ground (Add the forces), and wind
resistance works in the opposite direction of the force that the quarterback
applies to the ball (Subtract the forces).
What are Newton's Laws of Motion?
Sir Isaac Newton is credited with the
development of three laws of motion that have governed classical mechanics
. Newton's Laws of
Motion are:
1. An object at rest stays at rest and an
object in motion stays in motion unless acted upon by an outside force. (To
read more about Newton's First Law of Motion, see this article.)
2. Force is equal to an object's mass
times its acceleration. (To read more about Newton's Second Law of Motion, see
this article.)
3. For every action, there is an equal and
opposite reaction. (To read more about Newton's Third Law of Motion, see this
article).
What role does friction play?
Friction is a force that opposes
motion. It occurs when two surfaces rub past each
other. Every surface has a different coefficient of friction. This coefficient
of friction essentially tells us how "rough" the surface is. The greater the coefficient of friction, the more "rough" the surface. When an object moves through the air, we call the resulting frictional force wind resistance, or drag.
Aerodynamics is the study of forces and
the resulting motion of objects through the air. Essential aerodynamics looks
at ways to reduce wind resistance. To read more about aerodynamics, see this
article.
Answer
to the Question
Basically, the reason to throw a football in a spiral has to
do with the most efficient way to move the football through the air. The spiral helps to reduce the amount of
surface area the ball is exposed to. This
lowers the effect of wind resistance on the ball, and it allows the ball to
travel at a greater speed and a further distance.
____________________________________________
STYROFOAM
GLIDER
See
how different structural changes influence the distance it travels.
Try This!
To investigate air resistance,
aerodynamics and forces, try making a styrofoam glider. Possible variables to study:
- Effect of mass on distance
- Effect of length of fuselage on distance
- Effect of length of wing on distance
- Effect of length of tail on distance
- Effect of wing shape on distance
- Effect of tail shape on distance
- Effect of fuselage shape on distance
Materials:
- Scissors
- Styrofoam plate
- Paper clips
Design:
1. Using the scissors, cut a fuselage,
wing and tail out of the plate.
2. Take the fuselage and, using the
tip of the scissors, cut a hole in the middle for wings.
3. On the back end of the fuselage,
clip out a small triangle to insert the
tail.
4. Place a paper clip on the nose of
the plane for support.
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