Can anyone give me notes of motion chapter for 9th grade.
Answers
Answer:
Distance:
Length of path covered by a moving an object in the given time irrespective of the direction
is called distance.
It is a scalar quantity.
Its SI unit is metre(m).
Displacement:
The shortest distance measured from initial to the final position of an object is known as the displacement.
It is a vector quantity.
Uniform Motion:
When an object covers equal distances in equal intervals of time, it is said to be in uniform motion.
Non-Uniform Motion:
When an object covers unequal distances in equal intervals of time, it is said to be in non-uniform motion.
Speed (s):
The distance travelled by an object in unit time is referred to as speed.
It is represented as:
Formula for Speed
Its SI unit is metre/ second (m/s).
It is a scalar quantity.
Average speed: For non-uniform motion, the average speed of an object is obtained by dividing the total distance travelled by an object by the total time taken.
Formula for Average Speed
Velocity (v):
Speed of an object in a particular direction is named as velocity, i.e., it is the displacement of body in unit time.
It is represented as:
Jagranjosh
It is a vector quantity.
Average velocity: It is given by the arithmetic mean of initial velocity and final velocity for a given period of time.
Jagranjosh
Acceleration (a):
The rate of change of velocity is termed as acceleration.
It is represented as:
Formula for Acceleration
Its SI unit is metre/seccond2 (m/s2).
It is a vector quantity.
The acceleration is taken to be positive if it is in the direction of velocity and negative when it is opposite to the direction of velocity.
Negative acceleration is also named as retardation or deacceleration.
An object moving on a circular path though with uniform speed, is always said to be accelerated as it changes its direction every moment.
Uniform acceleration: When velocity of body changes by equal amounts in equal time intervals, acceleration is said to be uniform. For example: Motion of a freely falling ball.
Non - uniform acceleration: When velocity of body changes by unequal amounts in equal intervals if time, acceleration is said to be non - uniform. For example: Motion of car.
Graphical Representation of Motion
1. Distance -Time Graph for Uniform Speed:
Distance -Time graph for uniform speed, is a straight line as shown below:
Distance Time Graph for Uniform Speed
2. Distance -Time Graph for Non-Uniform Speed:
Distance -Time graph for uniform speed, is obtained in the form of a curve as shown below:
Distance Time Graph for Non Uniform
3. Distance -Time Graph for a Body at Rest:
Distance -Time graph for a body at rest is a straight line parallel to the time axis (x-axis):
Distance Time Graph for Body at Rest
Velocity-Time Graph
1. Velocity-Time Graph for Uniform Acceleration:
Velocity-Time graph for uniform acceleration is a straight line as shown below:
Velocity Time Graph for Uniform Acceleration
2. Velocity-Time Graph for Non-Uniform Acceleration:
Velocity-Time graph for non-uniform acceleration is obtained as a zig-zag line as shown below:
Velocity Time Graph for Non Uniform Acceleration
- To describe the position of an object we need a reference point or origin. An object may seem to be moving to one observer and stationary to another.
- Example: A passenger inside a bus sees the other passengers be at rest, whereas an observer outside the bus sees the passengers are in motion.
- In order to make observations easy, a convention or a common reference point or frame is needed. All objects must be in the same reference frame.
Distance and Displacement
The magnitude of the length covered by a moving object is called distance. It has no direction.
Displacement is the shortest distance between two points or the distance between the starting and final positions with respect to time. It has magnitude as well direction.
Displacement can be zero, but distance cannot.
Magnitude
Magnitude is the size or extent of a physical quantity. In physics, we have scalar and vector quantities.
Scalar quantities are only expressed as magnitude. E.g: time, distance, mass, temperature, area, volume
Vector quantities are expressed in magnitude as well as the direction of the object. E.g: Velocity, displacement, weight, momentum, force, acceleration etc.
Time, Average Speed and Velocity
Time and speed
Time is the duration of an event that is expressed in Seconds. Most physical phenomena occur with respect to time. It is a scalar quantity.
Speed is the rate of change of distance. If a body covers a certain distance in a certain amount of time, its speed is given by
Speed = DistanceTime
Average speed = Total distance travelled / Total time taken
Uniform motion and non-uniform motion
When an object covers equal distances in equal intervals of time it is in uniform motion.
When an object covers unequal distances in equal intervals of time it is said to be in non-uniform motion.
Velocity
The Rate of change of displacement is velocity. It is a vector quantity. Here the direction of motion is specified.
Velocity = DisplacementTime
Average velocity = (Initial Velocity + Final velocity)/2
Acceleration
The rate of change of velocity is called acceleration it is a vector quantity. In non-uniform motion
velocity varies with time, i.e change in velocity is not 0. It is denoted by “a”
Acceleration = Change in Velocity / Time