```Newton"s Third Law of Motion                              If the dynamics of a system is described
by a differential equation (or a system of
   Every action have equal and opposite                   differential equations), then equilibria can
reaction.                                              be estimated by setting a derivative (all
   The third law states that all forces exist in          derivatives) to zero.
pairs: if one object A exerts a force FA on
a second object B, then B simultaneously           There are three states of equilibrium:
exerts a force FB on A, and the two forces
are equal and opposite: FA = −FB                   1. Neutral equilibrium means that, with a
   The third law can be used to explain the               small deviation, the body remains in
generation of lift by a wing and the                   equilibrium. An example is a wheel rolling
production of thrust by a jet engine.                  on a horizontal surface. If you stop it at
any point, the wheel will be in a state of
Momentum (p)                                               equilibrium. A ball lying on a flat
horizontal surface is in a state of neutral
   It refers to the quantity of motion that an            equilibrium.
object has. It can be also defined as "mass        2. Unstable equilibrium means that, with a
in motion."                                            small deviation of the body from the
   Linear momentum or translational                       equilibrium state, forces emerge which
momentum is the product of the mass and                tend to increase this deviation. A ball
velocity of an object.                                 located at the top of a spherical projection
   It is a vector quantity.                               is an example of unstable equilibrium.
3. Stable equilibrium means that, with small
   p  mv
deviations of the body from this state,
   Where p = linear momentum, m = mass, v                 forces or moments of forces emerge which
= velocity                                             tend to return the body to the state of
equilibrium. A ball located at the bottom
Impulse (I) or (J)                                         of a spherical deepening is in a state of
stable equilibrium.
   It is defined as the integral of a force with
respect to time, which gives you the               Friction (μ)
change in the momentum of the body
being acted on by the force.                          It is the force between surfaces in contact
   Its unit is newton second (Ns)                         that resists their relative tangential motion
   The quantity of impulse is force × time                (slipping).
interval.                                             The force of friction is a force that resists
motion when two objects are in contact.
Inertia                                                   Friction is high for dry and rough surfaces
and low for smooth and wet surfaces.
   It is the resistance of any physical object           Rolling Friction occurs when an object
to any change in its state of motion (this             rolls over another (something with wheels
includes changes to its speed, direction or            or that is circular like a ball). e.g. riding a
state of rest).                                        motorcycle
   It is the tendency of objects to keep                 Fluid Friction occurs when an object
moving in a straight line at constant                  moves through a fluid, meaning either a
velocity.                                              liquid or gas. e.g. skydiving, swimming
   Sliding Friction occurs when solid
Equilibrium                                                surfaces slide over each other. e.g. falling
on the pavement
   It is the condition of a system when                  Lubricated friction is a case of fluid
neither its state of motion nor its internal           friction where a fluid separates two solid
energy state tends to change with time.                surfaces.
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