Momentum and Collisions

Momentum: Definition

Momentum is a vector quantity used to describe the motion of an object. Its direction is parallel to the motion of that object.

 p = m v

p ⇒ momentum (kg m/s or N s)
m ⇒ mass Mass Three-dimensional lesion that occupies a space within the breast Imaging of the Breast (kg)

The law of conservation of momentum

The law of conservation of momentum states that in an isolated system that does not have any interaction with its environment, all momentum is constant. When 2 objects collide, the total momentum of these 2 objects before the collision is equal to their total momentum after the collision.

Impulse

Impulse can be defined as the change in momentum over time caused by an average force. It is defined as follows:

I^→ ⇒ impulse (kg m/s)

F_av ⇒ average force (N or kg m/s²)
p ⇒ momentum (kg m/s or N s)
Δt ⇒ duration of the impulse (s)

Moment of Inertia

A static/rigid body has resistance Resistance Physiologically, the opposition to flow of air caused by the forces of friction. As a part of pulmonary function testing, it is the ratio of driving pressure to the rate of air flow. Ventilation: Mechanics of Breathing. Once a force sets a rigid body in rotating motion, a moment of inertia occurs. Moment of inertia depends on the body’s mass Mass Three-dimensional lesion that occupies a space within the breast Imaging of the Breast distribution in relation to the axis Axis The second cervical vertebra. Vertebral Column: Anatomy.

J ⇒ moment of inertia (kg m²)
r ⇒ axis Axis The second cervical vertebra. Vertebral Column: Anatomy of rotation Rotation Motion of an object in which either one or more points on a line are fixed. It is also the motion of a particle about a fixed point. X-rays
ρ ⇒ mass Mass Three-dimensional lesion that occupies a space within the breast Imaging of the Breast distribution

Angular momentum

Angular momentum can be thought of as ‘swirl’ or ‘spin’. It describes the direction and speed of a rotation Rotation Motion of an object in which either one or more points on a line are fixed. It is also the motion of a particle about a fixed point. X-rays about an axis Axis The second cervical vertebra. Vertebral Column: Anatomy. Angular momentum increases under the following conditions:

• the bigger the body’s mass Mass Three-dimensional lesion that occupies a space within the breast Imaging of the Breast
• the higher the body’s velocity
• the longer the distance from the axis Axis The second cervical vertebra. Vertebral Column: Anatomy

The following equation defines angular momentum:

L = r p

Collisions

Central collision

Δp ⇒ collision [(kg m)/s]

A collision can be defined as a change in momentum over time. The following equation defines collision:

Δp = F Δt

There are 2 types of collision:

• Elastic Elastic Connective Tissue: Histology collision: Kinetic energy is conserved.
• Inelastic collision: A part of the kinetic energy is converted into internal energy.

If the centers of gravity of the colliding bodies move along a straight line, such collision is defined as a straight-line central collision.