Projectiles
A projectile is
defined as an object which is given an initial velocity and than allow to move
under the influence of gravity. The body itself is a projectile in any jump or
dive and therefore , its path is determined in the same way as that of a thrown
or struck object. There are three forces that act on any projectile.
a) Gravity
b) Air resistance
c) Initial force which put it in motion.
Therefore, projectile
carries out two independent motions, a horizontal motion which is gradually
decreased by air resistance, a vertical motion which is affected by force of
gravity.
The distance
that a projectile travels depends upon its initial speed and the angle at which
it is projected.
Examples - When
air resistance is not taken in to consideration, the optimum angle of
projection, maximum distance is 45 degrees If the purpose of projection is
speed rather than distance, the angle should be as low as possible to carry the
required distance. The greater the speed of projection the lower the angle can
be for a given distance.
Water
Registance
1-
Buoyancy (Floating)
2-
Specific Gravity
3-
Concept of water resistance
4-
How to reduce water resistance
Buoyancy - The
term related to aquatic activities and may be defined as the “upward force of
the liquid on the wholly or partially immersed body”.
The concept of buoyancy comes from the Archimedes
principles, which state that a body immersed in a fluid is buoyed up by a force
equal to the Wt of the fluid displaced by the body.
Specific gravity - Some lean muscular people usuallymen are
sinkers, and can’t be taught to flot because the ratio of the body density to water density.
The ratio is found by
dividing the body Wf by displaced water’s lot.
If ratio is
above 1, it indicate that displaced water wf is less, the body will sink. If it
is less than 1, the body will flot.
Specific
gravity - is the ratio of the body density to the water
displaced.
Specific
gravity = wf of the body < 1
Wf of
displaced water
Concept of
water resistance :- It is a particular problem in swimming. The
resistance to the motion of body is sailed through on a liquid which increase
with its velocity. The force applied reaches the certain limiting value at
which the resistance due to friction is equal to the applied force has been
reached them velocity remain constant as long as force is applied.
So important that who to
over come the water resistance or can reduce further.
The following
factors (effecting water resistance)
