|
Physics is the
branch of science that deals with (surprise!) the physical world and its
properties. It attempts to explain in mathematical terms the behaviour of
matter as we observe it. To understand why soccer balls curve, how high
they bounce, how the pressure in the ball affects the bounce and even what
sort of boots to wear, we need to use things like Newton's laws of motion,
Bernoulli's discoveries about fluid flow, Maxwell's equations of
electromagnetics, Einstein's theories of gravitation and relativistic
motion, and a lot of other complicated-but-cool stuff.
On this page you'll get a glimpse of the
fascinating world of soccer physics.
For more
soccer physics go to:
http://www.madsci.org/posts/archives/nov98/912136446.Ph.r.html
To get an
understanding of the basics of physics:
http://physics.webplasma.com/physicstoc.html |
|
You might be
taking a long, slow strike at the ball rather than a shorter, sharp
strike. This is because a big windup doesn't necessarily impart sufficient
kinetic energy (mass x velocity squared divided by 2). This explains why
short, stocky players can generate power on the ball--a short, fast strike
contributes to kinetic energy as a square versus the linear increase of
weight alone.
Also your
head might be coming up on the strike - if you look up as the ball leaves
your foot, you impart less mass and velocity, ergo less kinetic energy.
|
This is a
bird's-eye view of a football spinning about an axis perpendicular to the
flow of air across it. The air travels faster relative to the centre of
the ball where the periphery of the ball is moving in the same direction
as the airflow (left). This reduces the pressure, according to Bernoulli's
principle. The pressure increases on the other side of the ball, where the
air travels slower relative to the centre of the ball (right). There is
therefore an imbalance in the forces, and the ball deflects in the same
sense as the spin - from bottom right to top left. This lift force is also
known as the "Magnus force", after the 19th-century German physicist
Gustav Magnus.
Assuming that the
velocity of the ball is 25-30 ms-1 (about 70 mph) and that the
spin is about 8-10 revolutions per second, then the lift force turns out
to be about 3.5 N. The regulations state that a professional football must
have a mass of 410-450 g, which means that it accelerates by about 8 ms-2.
And since the ball would be in flight for 1 s over its 30 m trajectory,
the lift force could make the ball deviate by as much as 4 m from its
normal straight-line course. Enough to trouble any goalkeeper!
Playing soccer on
the Moon
During an Apollo 17 Lunar landing mission, the astronauts took time out to
play a game of soccer on the surface of the Moon with a 200 lb. moon rock.
How? The "weight" of an object on the Moon is 1/6th that on Earth. (its
mass, of course, remains the same) |
 THAT'S THE
WAY
THE BALL BOUNCES!
Suppose a
soccer ball is dropped from rest at a height of 10 feet. And assume,
on each successive bounce, the ball reaches half the previous height
attained. How long will it take for the ball to finally come to
rest?
Surprisingly, most people immediately and incorrectly guess that the
time involved would be infinite. But, the time of each bounce
shortens quickly, and using the simple expression d=½ × g × t² for
the distance (d) travelled from rest during the time (t) under
gravity (g=32 feet/sec/sec), an infinite series leads to a
finite time of 4.61 seconds for the ball to come to rest. |
SUMMER SPECIAL!
Quote 'July1' at the checkout to get a massive 20% discount - only during
July.
