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Friction is a contact force that act between two objects that move past each other. Friction force is
parallel to the surfaces in contact and act in a direction that opposes the motion. Friction was
introduced first by Galileo
Without air friction, all objects heavy and light would reach the ground at the same time dropped
from the same height and at the same time
In the absence of friction force, an object does not need a force to keep it moving
Galileo’s experiments on motion: Forces and friction
A ball rolling down an inclined plane (a) speeds up because of gravity. A ball rolling up an
incline plane (b) slows down because of gravity
(a)
(b)
If friction could be eliminated then the initial and final heights of the ball are equal ((c), and (d)),
or the ball will never stops (e).
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________________
(c)
(d)
(e)
1.3 Scalars and Vectors
A Scalar is a physical quantity that has magnitude only. Mass, length, time, and temperature are examples
of scalar quantities. A scalar can be described by a number with a unit. For example, the length of an
object is 3 meters and its mass is 10 kilograms.
A vector is a physical qu