THE APPLICATION OF THE SCIENCE OF PHYSICS - PART II
Let us now study more important theories of Physics
applicable to Landsailing.
Ø Newton’s First Law Of Motion: It states that every body continues in its state of rest or of uniform motion in a straight line unless compelled by some external force to act otherwise.
The yacht is in its state of rest till the sail is set at
the appropriate angle and the wind – the external force – compels it
Ø Newton’s Second Law Of Motion: It states that the rate of change of momentum of a body is directly proportional to applied force and takes place in the direction of the force.
The applied force is wind – the body, i.e., the yacht
moves in the direction of the wind.
Ø Newton’s Third Law Of Motion: It states that to every action, there is an equal and opposite reaction.
o The power that pushes it also drags it.
Center Of Gravity: The center
of gravity of a body is the point fixed relative to the body through
which the weight of the body acts in whatever position the body may be
If the weight of the yacht is 20 kg, then
the wind force may require only half the effort to move it compared to a
40 kg yacht.
The important physical principle which governs yacht sailing is:
Moment of a couple: The moment of a couple is equal
to the product of one of the forces and the perpendicular distance
between the lines of action of the forces. The moment of a couple is
“torque”, (i.e., the force of power that makes something turn around
a central point). It is a “vector” (i.e., a quantity that has a
direction as well as a size usually represented by an arrow). Its
direction is perpendicular to plane of rotation given by the right hand
rule (Right hand rule states that if the fingers of the right hand curl
round the axis of rotation in the direction of rotation, then the thumb
represents the direction of angular displacement vector. The length of
the arrow gives the magnitude. (Couple: A pair of equal, unlike,
parallel and non-collinear forces acting on a rigid body is called a
couple). The body is yacht and the force is wind.
Displacement Vector: If an object changes its
position from a point A to B, then the vector will tail A and Tip B and
AB is the displacement vector. It may be noted that in its actual motion
the object may not have traveled along the straight line A to B at all.