Summary
Newton’s first law: An object at rest stays at rest, and an object in motion
stays in motion. No force means no change in velocity.
Newton’s second law: Acceleration (a) is directly proportional to the net
applied force (Fnet) and inversely proportional to the object’s mass (m): Fnet
= ma.
Newton’s third law: For every action (or force) there is an equal and opposite
reaction (force). The forces are equal in magnitude, opposite in direction, and
act on different bodies.
The weight of an object is the gravitational pull exerted on it by the planet on
which the object exists. Mass, conversely, does not change with location; it is
a measure of an object’s inertia.
The normal force is the component of the contact force that’s perpendicular to
the surface when an object is in contact with the surface.
Friction is the component of the contact force that is parallel to the surface
when an object is in contact with the surface.
Kinetic (sliding) friction occurs when there is relative motion (the object is
actually sliding across the floor).
Static friction occurs when there is no relative motion (the object is still or is
rolling without slipping).
Pulleys change the direction of the tension force in the cords that slide over
them.
An inclined plane is a ramp. When an object is on the inclined plane, then the
force of gravity Fw = mg has two components: one parallel to the ramp (mg sin
θ ) and one that’s normal (perpendicular) to the ramp (mg cos θ ), where θ is
the inclined plane.
Newton’s law of gravitation states that any two objects in the universe exert
on each other a gravitational force whose strength is proportional to the
product of the object’s masses and inversely proportional to the square of the
