LAWS OF MOTION

Force

A push or pull on an object. An interaction that can change an object's motion. SI unit is the newton.

Balanced Forces

Forces acting on an object that are equal in magnitude and opposite in direction resulting in no change in motion.

Unbalanced Forces

Forces acting on an object that are not equal in magnitude or are not acting in opposite directions resulting in a change in motion.

Motion

The change in the position of an object over time relative to a reference point.

Inertia

The tendency of an object to resist changes in its velocity or state of motion.

Law of Inertia

An object will continue to be at rest or continue moving with constant velocity unless acted upon by an unbalanced force. Also known as Newton's First Law of Motion.

Contact Forces

Forces that act only when two objects are in direct physical contact with each other.

Non Contact Forces

Forces that act on an object without requiring direct physical contact between objects. Also called at a distance forces.

Vector Quantity

A physical quantity that has both magnitude and direction.

Newton N

The SI unit of force. One newton is the amount of force needed to accelerate a one kilogram object by one meter per second squared. One newton equals one kilogram meter per second squared.

Mass

The amount of matter in an object. SI unit is the kilogram.

Weight

The force of gravity acting on an object.

Free Body Diagram

A simplified drawing that shows all the forces acting on an object including their direction and relative magnitude.

Net Force

The vector sum of all the forces acting on an object. It is the overall force after combining all individual forces while considering their directions. SI unit is the newton.

Acceleration

The rate at which an object's velocity changes over time. It may involve speeding up slowing down or changing direction. SI unit is meters per second squared.

Law of Acceleration

The acceleration of an object equals the net force acting on it divided by its mass. Expressed as F equals ma or a equals F divided by m. Also known as Newton's Second Law of Motion.

Mass and Acceleration Relationship

At constant force acceleration decreases as mass increases.

Direction of Acceleration

An object accelerates in the same direction as the net force acting on it.

Force of Gravity

The gravitational force acting on an object. Calculated using F equals mg.

Friction Force

The force that opposes motion between two surfaces in contact. Calculated using friction force equals coefficient of friction multiplied by normal force.

Coefficient of Friction

A number that describes how slippery or rough two surfaces are when rubbed together. Typical values range from zero point one to one point zero. Smaller values indicate smoother surfaces while larger values indicate rougher surfaces.

Normal Force

The support force exerted by a surface on an object that is in contact with it and acts perpendicular to the surface.

Free Fall

The motion of an object when gravity is the only force acting on it. Air resistance is ignored.

Air Resistance

The force exerted by air that opposes the motion of a moving object.

Terminal Velocity

The constant speed a falling object reaches when air resistance balances the force of gravity. At this point there is no acceleration.

Before Terminal Velocity

Gravity is greater than air resistance so the object accelerates downward.

At Terminal Velocity

Gravity equals air resistance so the net force is zero and the object moves at constant speed.

Acceleration Due to Gravity

The acceleration caused by Earth's gravity. Near Earth's surface it is approximately nine point eight meters per second squared downward.

Falling Objects in a Vacuum

In a vacuum all objects fall at the same rate regardless of their mass or surface area because there is no air resistance.

Terminal Velocity and Mass

An object with greater mass has greater weight and requires greater air resistance to balance its weight resulting in a higher terminal velocity.

Interaction

A mutual action between two objects where each object exerts a force on the other. Every interaction involves at least two objects.

Action Force

The force exerted by one object on another during an interaction.

Reaction Force

The force exerted back by the second object on the first. It is equal in magnitude and opposite in direction to the action force.

Law of Interaction

For every action there is an equal and opposite reaction. Whenever two objects interact each exerts a force on the other that is equal in magnitude and opposite in direction. Also known as Newton's Third Law of Motion.

Newton's Third Law Equation

F one equals negative F two meaning the forces are equal in magnitude but opposite in direction.