Newton's Third Law of Motion
Time for Action - Reaction Force Pair!
What is Newton's Third Law?
Newton's third law states that for every action, there is an equal and opposite reaction. One
easy example for you to visualize this is when you are walking: your foot exerts a force on
the
ground and the ground, in return, exerts an equal and opposite direction force on your feet,
allowing you to move forward.
Relation to Drone:
The rotating drone's propellers
push the air downward. According to Newton's Third Law of Motion, there is an equal and
opposite
reaction - an upward force, lift.
Next: More about Lift
Lift
What enable quadcopters to take off?
What is Lift ?
Lift is an upward force that acts against gravity. It is created by a solid object moving
through a fluid. Relating to our daily life, lift is the force that acts against the weight
of
an aircraft and enable the airplane to take off.
Relation to Drone:
If the magnitude of
lift is
greater than the weight of the drone, then the drone starts to ascend.If the magnitude of
lift
is equal to the weight of the drone, the net force is zero, and so the the drone hovers with
no
vertical movement.
Next: But what's stopping the drone from spinning ?
Torque
Equal torque acting in opposite direction cancels each other out.
How Is Torque Generated ?
If a force is applied to an object in such a way that makes it rotates, or stops rotate, a
torque is generated. Real life example of torque is when you open a door, or when you are
opening a bottle cap. In drone, torque is produced as each propeller rotates.
Relation to Drone:
As there is always an
equal and opposite force, the drone will rotate in the opposing direction of the propellers'
rotation direction if all of the drone' propeller rotate in the same direction. To prevent
the
drone from rotating, we make the drones' diagonal propeller pair (1,4) rotate clockwise,
while
the other diagonal pair rotate counter-clockwise. This way the net torque is equal to zero,
and
the drone has no rotaional movement.
Next: Ch.2 - Flight Dynamics