Chapter 4: Forces and Newton's Laws of Motion

Inertia

The natural tendency of an object to remain at rest or in motion at a constant speed along a straight line.

Inertial reference frame

A non-accelerating frame of reference in which Newton’s Law of Inertia is valid (at rest or moving with constant velocity).

Force

The push or pull required to change the state of motion of an object, as defined by Newton’s second law. A vector quantity, SI unit is Newtons (N)

Net force

The vector sum of all forces acting on an object, a vector quantity.

\sum F=ma

Equation for net force. Can also be divided into x and y components.

The velocity of an object can not change and the object can not accelerate.

The results of no net force acting on an object

Contact forces

Arise from physical contact.

\dfrac{kg\cdot m}{s^{2}}

SI unit for the Newton (N)

\dfrac{m}{s^{2}}

\dfrac{N}{kg} is equivalent to…

Newton's First Law of Motion

An object will continue in a state of rest or in a state of motion at a constant speed along a straight line unless compelled to change that state by a net force greater than zero.

Newton's Second Law of Motion

The acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass. The equation is F = ma, where F is the net force, m is the mass, and a is the acceleration.

Equilibrium

When the net force acting on an object is zero, it is in equilibrium and its velocity will not change.

Newton's Third Law of Motion

For every action, there is an equal and opposite reaction. When one object exerts a force on another object, the second object exerts an equal and opposite force on the first object.

Weight

Gravitational force that the earth (or other astronomical body) exerts on an object, always acts downwards, vector quantity, SI unit is the Newton.

W=mg

The equation for weight

Fundamental forces

The three fundamental forces are gravitational force, strong nuclear force, and electroweak force.

Newton's Law of Universal Gravitation

Every particle in the universe exerts an attractive force on every other particle. The force between two particles with masses m1 and m2 separated by a distance r is given by the equation F = G(m1m2/r^2), where F is the force, G is the universal gravitational constant, and r is the distance.

Normal Force

The component of a contact force that is perpendicular to the surface that an object contacts. It indicates how hard two objects press against each other.

Friction

The parallel force to a surface that opposes the motion or tendency of motion between two objects in contact.

Tension Force

The force applied by means of cables or ropes used to pull an object.

Equilibrium

Lack of change in the velocity of an object, where the object has zero acceleration.

Non-Equilibrium

When the net force acting on an object is not zero, causing the object to accelerate.