Motion By Dr Ajay Kumar Concept In physics

Motion By Dr. Ajay Kumar

Concept • In physics, motion is a change in position of an object with respect to time. • Change in action is the result of an unbalanced force. • Motion is typically described in terms of velocity, acceleration, displacement and time.

Cont. • An object's velocity cannot change unless it is acted upon by a force, as described by Newton's first law. • An object's momentum is directly related to the object's mass and velocity, and the total momentum of all objects in a closed system (one not affected by external forces) does not change with time, as described by the law of conservation of momentum.

Cont. • A body which does not move is said to be at rest, motionless, immobile, stationary, or to have constant (time-invariant) position.

Cont. • Motion is always observed and measured relative to a frame of reference. • As there is no absolute frame of reference, absolute motion cannot be determined; this is emphasised by the term relative motion. • A body which is motionless relative to a given reference frame, is still moving relative to infinitely many other frames. Thus, everything in the universe is moving.

Cont. • Linear motion is motion along a straight line, and can therefore be described mathematically using only one spatial dimension. • The linear motion can be of two types, Uniform Linear motion, with constant velocity or zero acceleration. • Non Uniform Linear motion, with variable velocity or non-zero acceleration.

• The motion of a particle (a point-like object) along a line can be described by its position x, which varies with t (time). Linear motion is also called as rectilinear motion.

• Linear motion is the most basic of all the motions. • According to Newton's first law of motion, objects that not subjected to forces will continue to move uniformly in a straight line indefinitely. • Under every-day circumstances, external forces such as gravity and friction will cause objects to deviate from linear motion and can cause them to rest at a point.

Definition • Translation or linear motion occurs if all parts of a body moves the same distance at the same time in the same direction. • For example: If a block is pushed on a horizontal surface. The block will undergo translation motion only.

• Another typical example of translation motion is the vertical motion of a lift in a shaft. • Another form of translation motion is curvilinear motion in which the object moves in a curved path but necessarily a circular pathway.

Rotational Motion - Concept • Rotation around a fixed axis is a special case of rotational motion. • The fixed axis hypothesis exclude the possibility of a moving axis, and cannot describe such phenomena.

Definition • Rotational or angular motion occurs when a body moves in a circular path such that all parts of the body moves through the same angle at the same time. • The angular motion occurs about a central line known as the axis of rotation which lies perpendicular to the plane of motion.

Cont. • For example : a gymnasts doing giant circle the center of gravity of the gymnast may undergo rotational motion with the centerline of the bar acting on the axis of rotation of the motion.

General Motion – Concept & Definition • The third class of motion is called the general motion which occurs if a body undergo translation and rotational motion simultaneously. • This motion is more complex to analyse as compared to pure translation or pure rotational motion.

• The diver is an example of a motion undergoing general motion. • Most human body segmental motion are of general type of motion. • For example : while walking the lower extremities both translate and rotate.

Cont. • The branch of kinematics that deal with the description of the translation motion is known as linear kinematics, and the branch that deals with the rotational motion is angular kinematics.