Class 9 Physics: Motion and Physical Quantities

Vocabulary flashcards covering scalar and vector physical quantities, kinematics equations, uniform circular motion, and graph interpretations from the class notes.

Scalar Quantity

A physical quantity that has magnitude only and is independent of direction, such as length, distance, and speed.

Vector Quantity

A physical quantity that possesses both magnitude and direction, such as force, displacement, velocity, and acceleration.

Distance

The overall or actual path length covered by an object. It is a scalar quantity that is always positive or zero and cannot be negative.

Displacement

The shortest length in a straight line between the initial position and final position. It is a vector quantity that can be positive, negative, or zero.

Speed

The rate of change of distance, defined as distance divided by time ($\text{distance} / \text{time}$). It is a scalar quantity that is always positive or zero.

Velocity

The rate of change of displacement, defined as displacement divided by time ($\text{displacement} / \text{time}$). It is a vector quantity that can be positive, negative, or zero.

Average Speed

The total distance covered by an object divided by the total time taken ($\frac{\text{total distance}}{\text{total time}}$).

Average Velocity

The total displacement divided by total time, or the arithmetic mean of initial velocity ($u$) and final velocity ($v$), calculated as $\frac{u + v}{2}$.

Acceleration

The rate of change of velocity over time, given by $a = \frac{v - u}{t}$. It is a vector quantity measured in $\text{m/s}^2$.

Retardation

Negative acceleration that represents a decrease in velocity over time, such as when brakes are applied to a moving vehicle.

Uniform Motion

Motion in which a body covers equal distances in equal intervals of time, where speed remains constant and acceleration is zero ($a = 0$).

First Equation of Motion

The kinematic formula $v = u + at$, derived from the rate of change of velocity formula $a = \frac{v - u}{t}$.

Second Equation of Motion

The kinematic formula for displacement $s = ut + \frac{1}{2}at^2$.

Third Equation of Motion

The kinematic formula $v^2 - u^2 = 2as$, connecting initial velocity ($u$), final velocity ($v$), acceleration ($a$), and displacement ($s$).

Uniform Circular Motion

Motion along a circular path where speed remains constant but direction continuously changes, rendering velocity variable and making it an accelerated motion.

Centripetal Acceleration

The acceleration in uniform circular motion that is directed towards the center of the circular track.

Slope of Displacement-Time Graph

The slope calculated as y-axis divided by x-axis ($\text{displacement} / \text{time}$), which represents the velocity of the object.

Slope of Velocity-Time Graph

The slope calculated as y-axis divided by x-axis ($\text{velocity} / \text{time}$), which represents the acceleration of the object.

Area Under Velocity-Time Graph

The area calculated under a velocity-time line using geometric formulas, which gives the total displacement of the object.