Mechanics

Force & Momentum

Force

is anything which has the potential to cause an object to acceleration

One newton

is that force which cause a body of mass of 1kg to undergo an acceleration

Force formulae

F= ma

Mass

a body is measure of how difficult it’s to acceleration that body

Friction

is a force which opposes the relative motion between two objects. E.g. Braking & walking

Momentum

is equal to its mass multiply by its velocity

Formulae for momentum

p = mv

What is the quantity of momentum?

The unit of momentum is kilogram meter per second (kg m s^-1) OR newton second (N s)

Principle of conservation of momentum

the total momentum before the interaction is equal to the total momentum afterwards provided no external forces act on the system.

principle of conservation of momentum formulae

m₁u₁ + m₂u₂ = m₁v₁ + m₂v₂

If one object collides with another & the two objects coalesce (stick together) then there’s only one velocity after collision 

m₁u₁ + m₂u₂ = (m₁ + m₂)v

Different direction must have different signs. Two objects with no momentum beforehand & they end up with equal & opposite momentum afterwards. E.g. Bullet sitting in a rifle.

0 = m₁v₁ + m₂v₂

Newton’s first law

every object will continue to travel at constant velocity unless an (unbalanced) external force acts on it

Newton’s second law

the rate of change of an object’s momentum is directly proportional to the force which caused it & takes place in the direction of the force

Newton’s third law

when objects interaction, they exert equal but opposite forces on each other

Terminal velocity

if an object is falling & reaches a stage where the upward force matches the downward force, then the object is no longer acceleration.

Impulse

change in momentum

Impluse formlae

I = mv - mu