1. Motion:
(i) Motion and rest are relative terms.
(ii) Reference point is the initial point from which a body starts moving.
(iii) When the position of a body changes continuously with respect to time and a reference point, the body is said to be in motion.
2. Speed:
(i) Speed is the rate of change of motion.
(ii) Speed=Total distance coveredTotal time taken
(iii) The basic unit of speed is m/s.
(iv) When a body covers equal distances in equal intervals of time, the body is said to be in uniform motion.
(v) When a body covers unequal distances in equal intervals of time, the body is said to be in non-uniform motion.
(vi) Speedometer present on the dashboard of a vehicle record speed in km/h.
(vii) Odometer is used to measure the distance.
3. Time:
(i) Time is defined as a gap between two events.
(ii) Second is the SI unit of time. It is equal to 186400th part of the solar day.
(iii) Time between the two successive noons is called solar day and is an ancient unit of time.
(iv) Ten years is equal to one decade, hundred years is equal to one century and thousand years is equal to one millennium.
(v) A body casts the longest shadow during sunrise or sunset and the smallest shadow during noon.
4. Devices to measure time:
(i) The stopwatch is a watch which can be started or stopped when desired. It is used to measure small intervals of time.
(ii) A digital clock is a clock in which time is displayed in digits by electronic circuits.
(iii) Sundial is a device used for measuring time, by measuring the length of shadow during the daytime.
(iv) Four sundials exist in India, i.e., in Jaipur, Varanasi, Ujjain and Delhi.
(v) Gnomon is a triangular plate fitted vertically on the horizontal surface of a sundial.
(vi) The sand clock is a device used by Romans to measure time. It works on the principle that a fixed mass of sand falls through a small hole in a fixed interval of time.
(vii) A sand clock is commonly called hourglass.
5. Pendulum:
(i) Pendulum is a heavy mass, called bob suspended from a rigid support using a string. When pulled to a side and released it oscillates about mean position.
(ii) Pendulum executes a periodic motion.
(iii) One oscillation means one to and fro motion of a pendulum about its mean position.
(iv) Time period is the time taken up by a pendulum to complete one oscillation.
6. Distance-Time graph:
(i) The motion of objects can be presented in pictorial form by their distance-time graphs.
(ii) The distance-time graph for the motion of an object moving with a constant speed is a straight line.
(iii) Bar graph and pie graph are also used to depict data.
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Definition: This type of motion is defined as the motion of an object in which the object travels in a straight line and its velocity remains constant along that line as it covers equal distances in equal intervals of time, irrespective of the duration of the time.
If a body is involved in rectilinear motion and the motion is consistent, then the acceleration of the body must be zero.
Example of Uniform Motion:
- If the speed of a car is 10 m/s, it means that the car covers 10 meters in one second. The speed is constant every second.
- Movement of blades of a ceiling fan.
Non Uniform Motion:
Definition: This type of motion is defined as the motion of an object in which the object travels with varied speed and it does not cover same distance in equal time intervals, irrespective of the time interval duration.
If a body is involved in rectilinear motion, and if the motion is not consistent, then the acceleration of the body must be non-zero.
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- If a car covers 10 meters in first two seconds, and 15 meters in next two seconds.
- The motion of a train.
Now, people usually get confused between uniform motion and uniform acceleration. In the later phenomena, the object is having a constant acceleration in rectilinear motion, which means the object has different speed in every second, which clearly defines that motion is changing.
Following is the table explaining concepts related to motion
|
Dynamics Of Circular Motion |
|
Introduction To Uniform Circular Motion |
Comparison table between these two types of motions:
|
Average Speed |
The motion is similar to the actual speed of the object. |
The motion is different from the actual speed of the object. |
|
Rectilinear Motion |
It has zero acceleration. |
It has non-zero acceleration. |
|
Graph |
Distance-time graph shows a straight line |
Distance-time graph shows a curved line |
|
Distance |
Covers equal distances in equal time interval. |
Covers unequal distances in equal time interval. |
Uniform Circular Motion:
This type of motion is seen if an object is travelling at a constant speed around a fixed axis or center point, and the object travels around a curved path and it maintains a constant radial distance from the center point at any given time and it moves in a tangent to the curved path.
Non Uniform Circular Motion:
This type of motion is inconsistent because if an object is travelling at a variable angular speed around a fixed axis or center point, then the motion of that object is said to be inconsistent because the object covers a curved path and it will have some variable radial acceleration due to which its velocity would change every second.
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