1 Physical quantities and units

Physical Quantity

A property that can be measured, characterized by a numerical magnitude and a unit.

SI Base Units

The seven fundamental units from which other units can be derived, including mass (kg), length (m), time (s), current (A), and temperature (K).

Scalar Quantity

A quantity that has magnitude but no direction. Examples include mass and energy.

Vector Quantity

A quantity that has both magnitude and direction. Examples include velocity and force.

Distance

A scalar quantity that measures how far an object has traveled, regardless of direction.

Displacement

A vector quantity that measures how far an object is from its starting point, including direction.

Speed

A scalar quantity that measures the distance traveled per unit of time.

Velocity

A vector quantity that measures the rate of displacement of an object per unit of time.

Random Error

Unpredictable fluctuations in measurement readings caused by uncontrollable factors affecting precision.

Systematic Error

Errors that occur consistently due to faulty instruments or flaws in experimental methods that affect accuracy.

Precision

Describes how closely multiple measurements of the same quantity are to each other.

Accuracy

Describes how close a measured value is to the true value.

Zero Error

A type of systematic error which occurs when an instrument gives a non-zero reading when the true reading is zero.

Absolute Uncertainty

Uncertainty expressed as a fixed quantity (e.g., 12.50 ± 0.05 cm).

Fractional Uncertainty

Uncertainty expressed as a fraction of the measurement.

Percentage Uncertainty

Uncertainty expressed as a percentage of the measurement.

Newton (N)

The SI unit of force, equivalent to kg·m/s².

Joule (J)

The SI unit of energy, equivalent to kg·m²/s².

Pascal (Pa)

The SI unit of pressure, equivalent to kg/(m·s²).

Kilo (k)

A prefix that denotes a factor of 10³, or 1,000.

Mega (M)

A prefix that denotes a factor of 10⁶, or 1,000,000.

Giga (G)

A prefix that denotes a factor of 10⁹, or 1,000,000,000.

Tera (T)

A prefix that denotes a factor of 10¹², or 1,000,000,000,000.

Deci (d)

A prefix that denotes a factor of 10⁻¹, or 0.1.

Centi (c)

A prefix that denotes a factor of 10⁻², or 0.01.

Milli (m)

A prefix that denotes a factor of 10⁻³, or 0.001.

Micro (µ)

A prefix that denotes a factor of 10⁻⁶, or 0.000001.

Nano (n)

A prefix that denotes a factor of 10⁻⁹, or 0.000000001.

Pico (p)

A prefix that denotes a factor of 10⁻¹², or 0.000000000001.

Acceleration

The rate of change of velocity of an object over time, measured in meters per second squared (m/s²).

Free Fall

The motion of an object under the influence of gravity alone, with no other forces acting on it.

Projectile Motion

The motion of an object that is thrown into the air and is subject to gravitational acceleration.

Newton's First Law

An object at rest stays at rest, and an object in motion stays in motion with the same speed and direction unless acted upon by a net external force.

Newton's Second Law

The acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass (F = ma).

Newton's Third Law

For every action, there is an equal and opposite reaction.

Mass

A measure of the amount of matter in an object, typically measured in kilograms (kg).

Weight

The force exerted on an object due to gravity, calculated as the product of mass and gravitational acceleration (W = mg).

Inertia

The tendency of an object to resist changes in its state of motion, directly related to its mass.

Uniform Motion

Motion at a constant speed in a straight line, where the acceleration is zero.

Instantaneous Velocity

The velocity of an object at a specific moment in time.

Average Velocity

The total displacement divided by the total time taken, representing the overall change in position during the motion.

Net Force

The vector sum of all forces acting on an object, determining its acceleration.

Frictional Force

The force that opposes the motion of an object, acting parallel to the surfaces in contact