Force and Momentum Concep
Understanding the concepts of inertia, mass, weight, pressure, volume,
density, specific weight, torque and impulse provides a useful foundation for
understanding the effects of forces.
(a) Concept and Definition
A force can be thought of as a push or pull acting on a body. Each force
is characterized by its magnitude, direction and point of application to a
given body. Body weight, friction, and air or water resistance are all
forces that commonly act on the human body. The action of force
causes a body’s mass to accelerate. Momentum, a mechanical quantity
that is particularly important in situations involving collisions. Momentum
may be defined generally as the quantity of motion that an object
possesses. More specifically, linear momentum is the product of an
object’s mass and its velocity. A static object (with zero velocity) has no
momentum; that is, its momentum equals zero. A change in a body’s
momentum may be caused by either a change in the body’s mass or a
change in its velocity.
(b) Application of Force and Momentum
Units of force are units of mass multiplied by units of acceleration. In the
metric system, the most common unit of force is the Newton(N), which
is the amount of force required to accelerate 1 kg of mass at 1 m/s2
Because a number of forces act simultaneously in most situations,
constructing a free body diagram is usually the first step when analyzing
the effects of forces on a body or system of interest. A free body is any
object, body, or body part that is being focused upon for analysis. When
all acting forces are balanced, or cancel each other out, the net force is
zero, and the body remains in its original state of motion, either
motionless or moving with a constant velocity. When a net force is
present, the body moves in the direction of the net force and with an
acceleration that is proportional to the magnitude of the net force. Units
of momentum are units of mass multiplied by units of velocity,
expressed in terms of kg m/s. Because velocity is a vector quantity,
momentum is also a vector quantity and is subject to the rules of vector
composition and resolution. When a head-on collision between two
objects occurs, there is a tendency for both objects to continue moving
in the direction of motion originally possessed by the object with the
greatest momentum.
Centripetal and Centrifugal Forces
Bodies undergoing rotary motion around a fixed axis are also subject to a
linear force. When an object attached to a line is whirled around in a circular
path and then released, the object flies off on a path that forms a tangent to
the circular path it was following at the point at which it was released, since
this is the direction it was travelling in at the point of release. Centripetal force
prevents the rotating body from leaving its circular path while rotation occurs
around a fixed axis. The direction of a centripetal force is always toward the
centre of rotation; this is the reason it is also known as centre seeking force.
Centripetal force produces the radial component of the acceleration of a body
travelling on a curved path. The magnitude of centripetal force depends on
the mass, speed, and radius of rotation of the rotating body. When rounding a
corner in a relay race, there is a sensation of being pushed in the direction of
the outside of the curve. What is felt has been referred to as centrifugal force.
This is because, according to Newton’s first law, the body’s inertia tends to
cause it to continue travelling on a straight, rather than a curved path.
Readings
Susan J. Hall. (1999). Basic biomechanics.(5th ed.). Boston: WCB/McGrawHill
Understanding the concepts of inertia, mass, weight, pressure, volume,
density, specific weight, torque and impulse provides a useful foundation for
understanding the effects of forces.
(a) Concept and Definition
A force can be thought of as a push or pull acting on a body. Each force
is characterized by its magnitude, direction and point of application to a
given body. Body weight, friction, and air or water resistance are all
forces that commonly act on the human body. The action of force
causes a body’s mass to accelerate. Momentum, a mechanical quantity
that is particularly important in situations involving collisions. Momentum
may be defined generally as the quantity of motion that an object
possesses. More specifically, linear momentum is the product of an
object’s mass and its velocity. A static object (with zero velocity) has no
momentum; that is, its momentum equals zero. A change in a body’s
momentum may be caused by either a change in the body’s mass or a
change in its velocity.
(b) Application of Force and Momentum
Units of force are units of mass multiplied by units of acceleration. In the
metric system, the most common unit of force is the Newton(N), which
is the amount of force required to accelerate 1 kg of mass at 1 m/s2
Because a number of forces act simultaneously in most situations,
constructing a free body diagram is usually the first step when analyzing
the effects of forces on a body or system of interest. A free body is any
object, body, or body part that is being focused upon for analysis. When
all acting forces are balanced, or cancel each other out, the net force is
zero, and the body remains in its original state of motion, either
motionless or moving with a constant velocity. When a net force is
present, the body moves in the direction of the net force and with an
acceleration that is proportional to the magnitude of the net force. Units
of momentum are units of mass multiplied by units of velocity,
expressed in terms of kg m/s. Because velocity is a vector quantity,
momentum is also a vector quantity and is subject to the rules of vector
composition and resolution. When a head-on collision between two
objects occurs, there is a tendency for both objects to continue moving
in the direction of motion originally possessed by the object with the
greatest momentum.
Centripetal and Centrifugal Forces
Bodies undergoing rotary motion around a fixed axis are also subject to a
linear force. When an object attached to a line is whirled around in a circular
path and then released, the object flies off on a path that forms a tangent to
the circular path it was following at the point at which it was released, since
this is the direction it was travelling in at the point of release. Centripetal force
prevents the rotating body from leaving its circular path while rotation occurs
around a fixed axis. The direction of a centripetal force is always toward the
centre of rotation; this is the reason it is also known as centre seeking force.
Centripetal force produces the radial component of the acceleration of a body
travelling on a curved path. The magnitude of centripetal force depends on
the mass, speed, and radius of rotation of the rotating body. When rounding a
corner in a relay race, there is a sensation of being pushed in the direction of
the outside of the curve. What is felt has been referred to as centrifugal force.
This is because, according to Newton’s first law, the body’s inertia tends to
cause it to continue travelling on a straight, rather than a curved path.
Readings
Susan J. Hall. (1999). Basic biomechanics.(5th ed.). Boston: WCB/McGrawHill
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