Class 9th Physics: Motion

Motion

The state of a body when it changes its position with respect to time and its surroundings.

Origin

The specified reference point used to describe the location or position of an object.

Scalar Quantity

A physical quantity that specifies only the amount, size, or magnitude of something, without providing any information about direction.

Vector Quantity

A physical quantity that specifies both magnitude and direction.

Distance

The total length of the path covered by an object from its starting point to its end point, regardless of direction; it is a scalar quantity.

Displacement

The shortest straight-line distance measured from the starting point to the end point of an object's motion; it is a vector quantity with the SI unit of metre ($\text{m}$).

Uniform Motion

A type of motion in which an object travels equal distances in equal intervals of time, maintaining a constant speed throughout its journey.

Non-Uniform Motion

A type of motion in which an object covers unequal distances in equal intervals of time because its speed keeps changing during its journey.

Speed

The distance travelled by an object per unit time ($\text{Average speed} = \frac{\text{total distance travelled}}{\text{total time taken}}$, or $v = \frac{s}{t}$); it is a scalar quantity with the SI unit of metre per second ($\text{m/s}$).

Velocity

The displacement of an object per unit time ($\text{Velocity} = \frac{\text{total displacement}}{\text{total time taken}}$). It is a vector quantity having both magnitude and direction.

Average Velocity

The mean value calculated when an object moves along a straight line at a variable speed, defined as $v_{\text{avg}} = \frac{u + v}{2}$, where $u$ is initial velocity and $v$ is final velocity.

Odometer

A device installed in an automobile that measures the total distance travelled by the vehicle.

Acceleration

The measure of the rate of change of velocity of an object per unit time, given by the formula $a = \frac{v - u}{t}$, where $u$ is initial velocity, $v$ is final velocity, and $t$ is time.

Uniform Acceleration

The acceleration of an object travelling in a straight line whose velocity increases or decreases by equal amounts in equal intervals of time (such as a free-falling body).

Non-Uniform Acceleration

The acceleration that occurs when the velocity of an object changes non-uniformly over time.

Slope of a Distance-Time Graph

The ratio of change in distance to change in time ($\text{Speed} = \frac{s_2 - s_1}{t_2 - t_1}$), which represents the speed of the moving object.

Distance-Time Graph for Uniform Speed

A line graph where distance is directly proportional to time taken, resulting in a straight line with a constant slope.