Understanding
the concept of forces is the basis for understanding
Newton’s laws. A force (F) is a push or pull that
one body exerts on another. The force is a vector
quantity, which has both magnitude and direction. It
represents the interaction of one body with another,
which may be recognized by actual contact or by action
at a distance. The force is characterized by its
magnitude, point of action, and direction.
Vectors
Manipulate the magnitude and direction of
two vectors to generate a sum.
Forces Lab
Gravitational
force is an example of actionatadistance force. It
is caused by the acceleration due to gravity. We
can measure the force of gravity or weight
of an object with a scale. Gravity is also the force
affecting the largest and smallest objects. This force
controls the movement of planets of the solar system in
orbit around the sun and the movement of stars in the
outer space.
The weight is distributed throughout the
body. But we may often think of it as collected and
acting through a single point called the centre of
gravity. The centre of gravity is a geometric property
of object. It is the average
location of the weight of an object. Center of gravity
is very important factor of stability. We may completely
describe the motion of any object through space in terms
of the translation of the center of gravity of the
object from one place to another and the rotation of the
object about its center of gravity if it is free to
rotate.
Online Simulation of Gravitational Force
Loads Lab
Shapes Lab
Measuring the Force
The force is
measured in Newton (N). One Newton is the amount of
force required to give a 1kilogram (kg) mass an
acceleration of 1 meters per second square (m/s^{2})
(Equation 6.1). We may use a simple spring scale such as
those used in the market. As the scale’s pan is pulled
down, the spring above is stretched and an attached
pointer moves. Then all we have to do to measure forces
is to calibrate the scale so that the amount of stretch
measures the magnitude of the force. This concept was
observed by Robert Hooke (16351703) and was named
Hooke’s law
of elasticity. Hooke’s law gives the relationship
between the force applied to an unstretched spring and
the amount the spring is stretched when the force is
applied



Where x is the
distance that the spring is stretched or compressed from
its relaxed length, and k is called the spring
constant for that particular spring in N/m. The spring
constant is a measure of how hard it is to stretch or
compress a spring. A stiffer spring has a larger spring
constant because larger forces must be exerted on the
ends of the spring to stretch or compress it.
The spring scale is a
weighting scale often used to measure force, such as the
force of gravity exerted on a mass or the force of a
person’s grip or the force exerted by a towing vehicle.
The above figure shows a
simple spring scale. Notice that there is a pull on both
ends of the scale; one pull is from the weight hanging
at the bottom of the scale and the other is from the
hook attached to the ceiling from above.
