Forces & Newton's Laws Vocabulary


A push or pull that one object exerts on another. May occur through direct contact or by action at a distance such as with a magnet or gravity.

Newton's First Law

Objects in motion tend to stay in motion and objects at rest tend to stay at rest, unless acted upon by an outside (unbalanced) force. ((Objects tend to keep doing what they are already doing))


The pull or force of Gravity acting on an object.

Newton's Second Law

An unbalanced (or Net) force acting on an object will cause the object to change its motion (accelerate).

Normal Force

A supporting (reaction) force that acts perpendicularly out of a surface in response to some other force pushing an object into a surface.

Equilibrium (of Forces)

Occurs when all forces acting on an object are balanced. When an object experiences an equilibrium of forces, there will be no change in the object's motion.

Frictional Force

Force that opposes motion between two surfaces that are in contact with one another. Friction acts parallel to the surfaces in contact and opposite the direction of motion.


Property of all matter, that makes matter "want" to, or "tend" to keep doing what it is already doing. Causes matter to "oppose" any changes in its motion.

Galileo Galilei

Famous Italian Physicist and Astronomer who was the first to suggest the idea of Inertia and the fact that Gravity accelerated all objects at the same rate regardless of their mass.

Isaac Newton

Famous English Physicist who proposed explanations to how force and motion are related with his Three Laws of Motion. Also developed a theory on what gravity was and how it worked.


The amount of matter (or stuff) in an object. Measured in Kilograms in Physics. The mass of an object does not change no matter where you go in the universe.

Units for Mass

SI unit: Gram, Physics Standard Unit: Kilogram

The "Newton

SI unit for Force. 1N = 1kg m/s2

Free Body Diagram

Diagram showing all the forces (and their directions) acting on an object.

Newton's Third Law

Every action has an equal and opposite reaction. Whenever an object exerts a force on another object, the other object exerts an equal magnitude and oppositely directed force back on the first object.

Balanced Forces

Forces that are equal in magnitude but opposite in direction that act on the same object. Balanced forces DO NOT cause any changes in an object's state of motion.

Unbalanced Forces

Two or more forces acting on an object in such a manner that there is more force in one direction than in the other direction(s). Unbalanced (Net) forces causes a change in an objects state of motion (acceleration).

Action-Reaction Forces

Related to Newton's Third Law-- Paired forces that come about due to objects exerting forces on each other.

State of Motion

The type of motion an object is experiencing-- Constant or Accelerated.

The "Applied Force

The applied force is the force which is applied to an object by a person or another object.

Tension Force

Any force applied through a string, rope, cable or chain--only capable of pulling--not pushing.

Net Force

The total amount of "Unbalanced" force acting on an object. The Net force is the amount of force that is not "cancelled out" when multiple forces are acting on and object.