Question

Explain Newton's Laws of Motion with an example.

Answer 1

Newton's First Law: "Every object persists in it's of rest or uniform motion in a straight line unless it is compelled to change that state by forces impressed on it."
Applied to rocket liftoff


Before firing:
The object in a state of rest, airspeed zero.
Engine fired:
Thrust increases from zero.
Weight decreases slightly as fuel burns.
When Thrust is greater than weight:
Net force (Thrust-Weight) is positive upward.
Rocket accelerates upward
Velocity increases

Newton's Second Law
Differential form: Force = change of momentum with change of time
$F=\frac{d\left(mv\right)}{dt}$
or:
Force= change in mass \times velocity with time
$F=\frac{(m_1{V}_1-m_0{V}_0)}{(t_1-t_0)}$
With mass constant: Force=$mass\times acceleration$ F=ma
Force, acceleration, momentum and velocity are all vector quantities. Each has both a magnitude and a direction.

Newton's Third Law: For every action, there is an equal and opposite reaction.
Rocket Engine Thrust