STUDY QUESTIONS
1. Define (a) rest, (b) motion. Give an example in
each case.
2. By giving two examples define :
(a) Rectilinear motion
(b) Curvilinear motion
(c) Rotatory motion
(d) Circulatory motion
3. By giving two examples define :
(a) Oscillatory motion
(b) Vibratory motion
(c) Periodic motion
(d) Non-periodic motion
Answers
Answer:
1. a) Rest is the state an object being stationary relative to a particular frame of reference or another object; when the position of a body with respect to its surroundings does not change with time it is said to be "at rest".
EXAMPLE: For example, a train decelerates approaching a station and eventually comes to rest alongside the platform. The train can be said to be "at rest with respect to the station", or, as the correct frame of reference is usually implicit and/or provided by context, simply "at rest".
b) Motion is the phenomenon in which an object changes its position over time. Motion is mathematically described in terms of displacement, distance, velocity, acceleration, speed, and time.
EXAMPLE: For example, a passenger sitting on a moving bus is at rest because he is not changing his position with respect to other passengers or objects on the bus. But to an observer outside the bus, the passengers and the objects inside the bus are in motion. Therefore we can define rest as “A body is said to be at rest if it does not change its position with respect to its surroundings.”
2. a) When we require only one co-ordinate axis along with time to describe the motion of a particle it is said to be in linear motion or rectilinear motion. Some examples of linear motion are a parade of soldiers, a train moving along a straight line, and many more.
b) The motion of an object moving in a curved path is called curvilinear motion. Example: A stone thrown into the air at an angle.
c) Rotary motion, also referred to as rotational motion or circular motion, is a physical motion that happens when an object rotates or spins on an axis.
d) Circular motion is a movement of an object along the circumference of a circle or rotation along a circular path. It can be uniform, with a constant angular rate of rotation and constant speed, or non-uniform with a changing rate of rotation.
3. a) * Oscillation of simple pendulum
* Vibrating strings of musical instruments is a mechanical example of oscillatory motion
b) * Movement of simple pendulum.
* Movement of swing.
c) * Rocking chair
* A bouncing ball
d) * The running of a batsman between the wickets.
* Movement of our hand while writing.
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Answer:
(1) Periodic motion : A motion that repeats itself at
definite intervals of time is said to be a periodic
motion.
Examples: The motion of the hands of a clock, the
motion of the Earth around the Sun.
(2) Oscillatory motion: A periodic motion in which a
body moves back and forth over the same path,
straight or curved, between alternate extremes is
said to be an oscillatory motion.
Examples: The motion of a taut string when
plucked, the vibrations of the atoms in a molecule,
the oscillations of a simple pendulum.
[Note: The oscillatory motion of a particle is also
called a harmonic motion when its position, velocity and
acceleration can be expressed in terms of a periodic,
sinusoidal functions-sine or cosine, of time.]