Transcript Projectiles in Sports

PROJECTILES
BY GREG ROYAL
DRURY HIGH SCHOOL
NORTH ADAMS, MASSACHUSETTS
A projectile is any that is given an initial horizontal or angular velocity, and
then follows a path determined entirely by gravity.
PROJECTILES IN SPORTS
•
A projectile is any object that is cast, fired, flung, heaved, hurled, pitched, tossed, or
thrown. (This is an informal definition.) The path of a projectile is called its trajectory.
Some examples of projectiles include…
•
a baseball that has been pitched, batted, or thrown
•
a bullet the instant it exits the barrel of a gun or rifle
•
a lacrosse ball being thrown by a lacrosse stick
•
a javelin or discus being thrown for distance
•
a runner in mid stride (since they momentarily lose contact with the ground)
•
A football being thrown or kicked
PROJECTILES AND SPORTS
•
All projectiles follow a path and obey the laws of gravity
•
Once an NFL kicker kicks a ball the ball becomes a projectile and follows a
path also known as “a parabolic curve”
•
A lacrosse player uses a lacrosse stick to increase the distance of the
lacrosse ball over the same period of time as his hands travel. Thereby
increasing the velocity (distance divided by time + direction)
GRAVITY
•
The force of primary importance acting on a projectile is gravity
•
Objects with mass are attracted to each other, this is known as gravity
•
Acceleration of objects to due to the gravity on Earth is 9.8 m/s2. If you ignore air
resistance (drag) then the speed of an object falling to Earth increases by 9.8 meters per
second every second (second squared)
FORCE PUSHING AN OBJECT
•
direction and rotation in flight are determined by the force pushing an object
•
a curve ball travels more slowly than a straight ball due to the force that is
generated off center into the spin by the air resistance to the laces, as well as the
retarding effect of air friction.
•
The force of gravity has a downward effect on flight as soon as contact with the driving
force (e.g., a bat, thrower's hand) is broken.
•
As speed increases, air resistance has a greater retarding effect on an object in flight.
• a javelin or discus should be released at an angle of tilt that exposes the least
surface area in flight in order to maximize throwing distance.
•
The optimum angle of projection is 45 degrees, assuming that the beginning and ending
points are at the same level.
• the angle of release for a shot put is closer to 42 degrees or less because it is
released well above the level of the landing area.
DISTANCE VERSES HEIGHT
•
distance the projectile flies depends upon the height it attains when launched which
depends on the angle it’s launched (best angle 45 degrees) and the initial velocity.
• a a football will travel the furthest if launched at a 45 degree angle if initoial velocity
is the same as a different angle.
•
The height an object achieves depends on the initial velocity at launch and is degraded
over time by the force of gravity
• For example, a springboard diver attempts to project himself high in the air in order
to allow time to complete the desired airborne movements therefore taking a Ballistic
path.
• The speed at take-off has an impact on the height or distance athletes (projectiles in
sports) jump. Training to build power fitness or the combination of speed and
strength, improve hang time in the air.
REBOUND OF PROJECTILE
•
The angle of rebound (reflection) of a projectile equals the angle at which it approaches a
surface (angle of incidence), but can be affected by irregular shapes, elasticity, and spin.
mathematically the angle of incidence= the angle of reflection
•
a basketball rebounds off a backboard at the same angle at which it approaches, unless it
is partially deflated or a player puts spin on it
•
a bank shot in billiards
CONSERVATION OF MOMENTUM
•
When both an object and the striking surface are moving, the momentum with which the
object will rebound equals the momentum of both
•
depending on the original direction of both objects this can be additive or subtractive
and whether they are joined together (inelastic collision) or bounce apart (elastic
collision)
•
For example, the striking force of a bat on a ball is determined by the momentum of both
objects. A fast-moving ball will rebound with greater velocity than a slow-moving ball,
provided the bat can overcome the inertia of the ball.
SPIN
•
An object propelled without spin tends to waver due to air resistance against an irregular
surface, but a small amount of spin produces stability.
• For example, a volleyball served with a slight spin follows a true course of flight.
•
An object spins in the desired direction when the striking implement is drawn across it in
the intended direction
• tennis players attempt to stoke the ball with a forward-upward motion in order to
impart topspin.
•
effects of spin on a ball landing on a horizontal surface as follows
• Topspin causes a lower angle of rebound, a longer bounce, and more roll.
• Backspin causes a higher angle of rebound, a shorter bounce, and less roll.
• Sidespin causes the angle of rebound to change toward the direction of the spin.