Cambridge O Level Physics · Syllabus 5054 · Motion, Forces and Energy
Inertia
What is Inertia?
Inertia is the property by which the mass of an object resists a change from its state of rest or of uniform motion. The larger the mass, the larger the force needed to produce a given acceleration.
This definition is part of the Motion, Forces and Energy chapter in Cambridge O Level Physics.
Inertia in context
Mass is a measure of the quantity of matter in an object at rest relative to the observer, measured in kilograms, and it is the property that resists a change from a state of rest or of motion — inertia. Weight is the gravitational force acting on that mass, measured in newtons. Gravitational field strength is force per unit mass, \(g = W/m\), measured in \(\mathrm{N/kg}\), and it is numerically equal to the acceleration of free fall. Move an object to the Moon and its mass is unchanged while its weight falls, because \(g\) there is smaller.
Questions students ask about Inertia
What is the difference between mass and weight?
Mass is a measure of the quantity of matter in an object, measured in kilograms, and it never changes; it is the property that resists a change in motion, called inertia. Weight is the gravitational force acting on that mass, measured in newtons, and it follows \(g\) wherever the object goes: \(W = mg\), with \(g\) approximately \(9.8\ \mathrm{N/kg}\) near the Earth. A balance compares masses; a force meter measures weight.