CDS Physics Digital Book

Units and Measurements

• Physical Quantity: A measurable property expressed as a value, e.g., mass, length, time.

• Fundamental Quantities: Independent quantities like Length (meter), Mass (kilogram), Time (second), Electric current (ampere), Thermodynamic temperature (kelvin), Amount of substance (mole), and Luminous intensity (candela).

• Supplementary Quantities: Dimensionless units used with base units to form derived units, such as Plane angle (Radian) and Solid angle (Steradian).

• Derived Quantities: Dependent quantities from a combination of fundamental quantities.

Motion

• Scalar Quantity: Has magnitude but no direction, e.g., mass, length, speed, time.

• Vector Quantity: Has both magnitude and direction, e.g., displacement, velocity, acceleration, force.

• Distance: The total path length traveled, a scalar quantity that is always positive.

• Displacement: The shortest distance between start and end points, a vector quantity that can be positive, negative, or zero.

• Speed (S): Distance (d) / Time (t); SI unit is m/s and is a scalar quantity that can never be negative.

• Velocity (v): Displacement (s) / Time (t); SI unit is m/s and is a vector quantity that can be zero, negative, or positive.

• Acceleration (a): Rate of change of velocity over time.

Force and Newton's Laws

• Force: An external effort that can change an object's state of motion, rest, or shape. It is a vector quantity, with the SI Unit being Newton (N).

• Newton's First Law (Inertia): A body remains at rest or in uniform motion unless an external force acts on it.

• Newton's Second Law: The rate of change of momentum is proportional to the applied unbalanced force (F=ma).

• Newton's Third Law: For every action, there is an equal and opposite reaction.

Gravitation

• Gravitation: The force of attraction between any two bodies. Acceleration due to gravity (g): g = 9.8m/s^{2} on Earth. The value of 'g' is highest on the poles and lowest on the equator.