Newton

Normal force

Normal force = N, the force or the component of a force which a surface exerts on an object with which it is in contact, and which is perpendicular to the surface.

Frictional force

Frictional force = f, the force that opposes the motion of an object and which acts parallel to the surface.

→ Static frictional force: fs, the force that opposes the tendency of motion of a stationary object relative to a surface.

→ Kinetic frictional force: fk, the force that opposes the motion of a moving object relative to a surface.

Newton's 1st law of motion

A body will remain in it's state of rest or motion at a constant velocity unless a non-zero net force acts on it.

Newton's 2nd law of motion

When a net force acts on an object, the object will accelerate in the direction of the force at an aceleration directly proportional to the force and inversely proportional to the mass of the object.

Newton's 3rd law of motion

When one body exerts a force on a second body, the second body exerts a force equal in magnitude and opposite in direction on the first body.

Newton's Law of Universal Gravitation

Each body in the universe attracts every other body with a force directly proportional to the product of their masses and inversely proportional to the squared distance between their centres.

Weight vs Mass

Weight: The gravitational force the Earth exerts on any object on or near it's surface.

Mass: An indication of the amount of matter of an object.

Weightlessness

The condition in which an object experiences an apparent weight of zero because no normal force acts on it. This usually occurs when the object is in free fall. The only force acting on the object is Fg.