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Dynamics
Newton’s Laws
A force is a physical quantity that can affect the
motion of an object. Since a force has magnitude,
direction, and a point of application, it is a vector
quantity.
Sir Isaac Newton was the first person to clearly
describe the relationship between force, mass &
motion. Newton's laws of motion not only apply on
Earth but are true throughout the universe.
Different Common Types of Forces
1. Buoyant Force - produced by fluids; acts upward
2. Elastic Force - produced by stretching, compressing, or twisting
an object
3. Electrical Force - produced by interaction between charged
particles
4. Frictional Force - produced when one surface moves over
another; acts in a direction resisting motion.
5. Gravitation Force produced by attraction of any two objects,
acts downward on Earth
6. Magnetic Force - produced by interaction of at least 1 magnet
and another object.
Newton's 1st Law of Motion: If there is no force
acting on a body, it will continue in its state of
rest or will continue moving along a straight
line with uniform speed
This law is known as the law of inertia.
is this object moving?
50 N
50 N
Newton's 2nd Law of Motion: The effect of an applied force
is to cause the body to accelerate in the direction of the
force. The acceleration is in direct proportion to the force
and in inverse proportion to the mass of the body.
In other words, the more force, the more
acceleration and the more mass, the less
acceleration.
F
a
m
•If a force is applied to a body at rest, the body will begin to
move.
•If the body is is moving in a straight line and a force is
applied in the direction of motion, the body will accelerate.
•If the force is applied in a direction not in line with the
motion, the acceleration will be in the direction of the force.
Reworking our proportion statement, we find we
get the equation:
F  ma
Units
F- Newtons (N)
m= kilograms (kg)
a = metres/sec./sec. (m/s2)
Combining the units for mass and
acceleration, we come up with the
unit for force kg m/s2. This has been
defined as one newton (1 N).
Newton's 3rd Law of Motion: When one body
exerts a force on another, the second body
exerts on the first a force of equal magnitude
in the opposite direction.
This occurs at all time in nature. There is always an action
force and a reaction force. For example, a book lying on
table exerts a force on the table and the table exerts a force
on the book.