Newton's First Law
Newton's First Law of Motion states that an object at rest remains at rest, and an object in motion continues in motion at constant velocity, unless acted upon by a net external force. This principle is also known as the Law of Inertia and forms the conceptual foundation of classical mechanics. It explains why passengers lurch forward when a bus brakes suddenly, or why a hockey puck slides indefinitely on a frictionless ice surface.
Newton's First Law — Examples in Daily Life
| Situation | Object State | External Force | Outcome |
|---|---|---|---|
| Book on a table | At rest | None (balanced) | Remains at rest |
| Bus braking suddenly | Passenger in motion | Seat belt / friction | Passenger lurches forward |
| Hockey puck on ice | Moving | Minimal friction | Continues moving |
| Satellite in orbit | Moving in a curve | Gravity (centripetal) | Follows curved path |
| Ball rolled on grass | Moving | Friction from grass | Gradually decelerates |
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Related Terms
Inertia
Inertia is the tendency of an object to resist any change in its state of motion — whether at rest or moving at constant velocity. It is not a force but a property of matter that depends directly on the mass of the object; greater mass means greater inertia. Inertia explains why a heavy truck requires much more braking force than a bicycle to stop in the same distance, and why it is harder to start a loaded cart moving than an empty one.
Newton's Second Law
Newton's Second Law of Motion states that the net force acting on an object equals the product of its mass and acceleration. It is the most quantitative of the three laws and provides the mathematical relationship between force, mass, and motion. This law is used in virtually every engineering and physics calculation involving dynamics, from designing car brakes to launching spacecraft.
Friction
Friction is a contact force that opposes the relative motion or tendency of motion between two surfaces in contact. It arises from microscopic interactions between surface irregularities and is directly proportional to the normal force through the coefficient of friction. Friction is essential in everyday life — it allows us to walk, cars to brake, and objects to remain stationary on inclined surfaces — but it also causes energy loss as heat in machines.
Named after Sir Isaac Newton, who published the three laws of motion in 'Philosophiae Naturalis Principia Mathematica' in 1687. The concept of inertia was earlier described by Galileo Galilei in the early 17th century. 'Newton' derives from a place name in Lincolnshire, England.