Physics 2.2 Newtons Laws

Force

A push or pull acting on an object due to an interaction with another object

Resultant force

The sum of all the individual forces acting on an object taking direction into account

Calculating resultant force

By adding together the vector arrows of all the individual forces

Newton’s first law for a stationary object

If the resultant force on a stationary object is zero the object remains at rest

Newton’s first law for a moving object

If the resultant force on a moving object is zero the object continues at constant velocity with the same speed and direction

Changing direction at constant speed

There must be a resultant force because velocity is changing

Zero resultant force effect

The object remains stationary or continues moving at constant speed in a straight line

Inertia

The tendency of an object to continue in its state of rest or uniform motion

Newton’s second law equation

Resultant force equals mass multiplied by acceleration F equals ma

Newton’s second law in words

Acceleration is directly proportional to resultant force and inversely proportional to mass

Inertial mass

A measure of how difficult it is to change an object’s velocity equal to force divided by acceleration

Newton’s third law

When two objects interact they exert forces on each other that are equal in size and opposite in direction

Weight

The force acting on an object due to gravity and its mass

Quantities affecting weight

Mass of the object and gravitational field strength weight equals mass times gravitational field strength

Unit of weight

Newton

Gravitational field strength on Earth

About 10 newtons per kilogram

Weight of a 1 kilogram mass on Earth

About 10 newtons

Terminal velocity

Reached when air resistance equals weight so there is no resultant force and speed is constant

Air resistance and velocity

As velocity increases air resistance increases