Newton's Laws of Motion

Study Notes

Newton's First Law: An object at rest stays at rest, and an object in motion continues to travel with constant velocity, unless acted on by an external force.
Inertia: The tendency of a body to keep moving once it is set in motion, or the tendency of a body at rest to remain at rest, results from a property called inertia.
Constant velocity: Means zero net force.

Reference frame: A rigid body whose particles can be labeled to create reference points, simplified by introducing a coordinate system.
Inertial reference frame: If no forces act on a body, any reference frame with respect to which acceleration of the body remains zero.
Newton's laws of motion: Valid only in inertial reference frame (non-accelerating and non-rotating).

Force: A push or a pull, an interaction between two objects or between an object and its environment.
Superposition of Forces: Any number of forces applied at a point on a body have the same effect as a single force equal to the vector sum of the forces.
Net force: The vector sum of the forces acting on an object.
Acceleration: The product of the mass of an object and the magnitude of its acceleration.
F ∝ a: The magnitude of force is proportional to the magnitude of acceleration.
F = ma: The net force acting on an object is equal to the mass of the object multiplied by its acceleration.

Mass: Measures the object's inertia, in kilograms (kg).
Weight: The gravitational force that the Earth exerts on an object, dependent on altitude and location.
W = mg: The weight of an object is equal to the mass of the object multiplied by the acceleration due to gravity.

Acceleration: Directly proportional to the net force acting on it, and inversely proportional to the mass of the object.
F = ma: The net force acting on an object is equal to the mass of the object multiplied by its acceleration.

SI system: Used in this course, where force is measured in Newtons (N), distance in meters (m), and mass in kilograms (kg).
British system: Force measured in pounds, distance in feet, and mass in slugs.
CGS system: Mass measured in grams, distance in centimeters, and force in dynes.

Action-reaction pair: If you exert a force on a body, the body always exerts a force (the "reaction") back upon you.
Collinear forces: Forces acting on different bodies, having the same magnitude but opposite directions.

Normal force: The force exerted on an object by any surface with which it is in contact, acting perpendicular to the contact surface.
Tension force: A pulling force exerted on an object by ideal strings, always measured parallel to the string.
Frictional force: A force exerted on an object by a surface, acting parallel to the surface, in the direction that opposes sliding or the tendency to slide.
Static friction: Acts when there is no relative motion between bodies, varying between zero and its maximum value.
Kinetic friction: Acts when a body slides over a surface, proportional to the normal force.
Rolling friction: The opposing force that comes into existence when one object rolls over the surface of another object.

Drag force: A force that depends on the shape of the object, the properties of the fluid, and the speed of the object relative to the fluid.
Retarding force: A force that opposes the motion of an object, proportional to the square of the velocity.

Free-body diagram: A single body or a subsystem of bodies isolated from its surroundings, showing all the external forces acting on it.
Steps for FBD: Identify the object or system, isolate it from other objects, draw non-contact external forces, and then draw contact forces.
Examples of FBD: Various scenarios, including a dog pulling a sled, a book on a tabletop, a gymnast holding onto a bar, and a skydiver descending with a constant velocity.