Transcript Newton`s Third Law

Newton’s 3rd Law
Action-Reaction Forces
For every action, there is an
equal and opposite reaction.
According to Newton, whenever two
objects interact with each other, they
exert forces upon each other.
The statement means that in every
interaction, there is a pair of forces acting
on the two interacting objects.
in a chair
your body exerts a downward force on the chair
the chair exerts an upward force on your body
two forces resulting from this interaction
a force on the chair
a force on your body
the two forces are called action and reaction forces
size of the force on the
first object equals the
size of the force on the
second object
direction of the force on
the first object is
opposite to the direction
of the force on the
second object
forces always come in
pairs
equal and opposite
action-reaction force pairs
Consider the propulsion of a
fish through the water
fish uses fins to push water backwards
a push on the water will only serve to
accelerate the water
water reacts by pushing the fish
forwards, propelling the fish through
the water
size of the force on the water equals
the size of the force on the fish
direction of the force on the water
(backwards) is opposite the direction
of the force on the fish (forwards)
Consider the motion of a bus
on the way to school.
bus is equipped has wheels that turn
wheels turn and grip the road and
push the road backwards
road reacts by pushing wheels forward
size of the force on the road equals the
size of the force on the wheels (or bus);
the direction of the force on the road
(backwards) is opposite to the
direction of the force on the wheels
(forwards)
While driving down the road, an unfortunate
bug strikes the windshield of a bus. Quite
obviously, this is a case of Newton's third law
of motion. The bug hit the bus and the bus
hits the bug.
Which of the two forces is greater, the force on
the bug or the force on the bus?
TRICK QUESTION!
The forces are equal.
The bug gets squashed because it isn’t built
to withstand the acceleration.