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Physics Worksheet
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Newton’s Third Law of Motion – Action and Reaction
Newton’s Law of Action and Reaction
a)
Newton’s third law: the law of action and reaction.
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a)
System: A systems is a coherent entity that has
_________________. A system can be characterized
and described by its
__________________________________________
_________________ and the ___________ between
__________________________________________
them. A system can be viewed as a collection of
__________________________________________
____________________ = ____________________
Name:
System Concept
__________________________________________
Newton’s third law formula:
Section:
____________________________.
b) Example: Identify the action and reaction
(interaction) of a vase placing on the table:
____________________ = ____________________
b) Force is not something an object has, like mass.
Force is an _____________ between two objects. To
every action there is always a _________________.
They are always:
If action is always equal to reaction, why don’t they
cancel each other out?
(1) _______________________________________.
__________________________________________
(2) _______________________________________.
(3) _______________________________________.
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c)
d) Example: Why Does the Man-Box Move?
i)
Identify all the horizontal forces of in a ManBox diagram:
Identifying Action and Reaction
a) An easy way to identify action and reactions forces is
to simply say:
Action:
Object A exerts a force on Object B.
Reaction: ________________________________.
ii) Identify all the horizontal forces of a Man
system:
b) Example: In the case of a falling boulder,
Action: the Earth exerting a force on the boulder.
Reaction: ___________________________________.
c) Example: In the case of hanging a lamp from ceiling,
iii) Identify all the horizontal forces of a Box
system:
Action: the ceiling exerting a force on the lamp.
Reaction: ___________________________________.
d) Example: In the case of hammering a nail,
Action: the hammer exerting a force on the nail.
iv) Identify all the horizontal forces of a Man-Box
system
Reaction: ___________________________________.
Mr. Lin
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Physics Worksheet
e)
Newton’s Third Law of Motion – Action and Reaction
Identify all the horizontal forces of in a HorseCart diagram:
ii) Identify all the horizontal forces of a Horse
system:
Name:
h) Example: A 100 N pushing force at 30o angle is
exerted on a 10 kg block against the wall. Identify
and calculate all the forces acting on the block by
drawing the free-body diagram
Example: Why Does the Horse-Cart Move?
i)
Section:
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Action and Reaction on Different Masses
a)
If action is equal to reaction, by applying Newton’s
second law, we can write:
___________________ = _____________________
iii) Identify all the horizontal forces of a Cart
system:
According to Newton’s second law, acceleration is
inversely proportional to the __________. So, the
larger the mass, the ___________ the acceleration.
iv) Identify all the horizontal forces of a HorseCart system
b) Example: When considering a boulder falling to
Earth, you can say Earth is also
_________________________________________.
Although the forces are equal, the masses are very
unequal. Since Earths mass is so large, the
f)
Example: Why does a Rear-Wheel-Drive Car move?
i)
acceleration of the boulder is __________________.
Identify all the horizontal forces of in a RearWheel-Drive Car diagram:
c)
Example: Based on the following diagram, calculate
the acceleration of the girl.
ii) Identify all the horizontal forces of a RearWheel-Drive Car system:
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Interaction through a String
a)
Example: Based on the info from diagram, (a) find
the readings of (b) and (c).
g) Example: Why Does the Horse-Cart Move?
i)
Identify all the horizontal forces of in a FrontWheel-Drive Car diagram:
ii) Identify all the horizontal forces of a FrontWheel-Drive Car system:
Mr. Lin
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Physics Worksheet
Newton’s Third Law of Motion – Action and Reaction
b) Example: Based on the info from diagram, find the
readings on both scales.
c)
Name:
Interaction with acceleration
a)
Weight in the Elevator: Analyze the weight changes
in an elevator due to different accelerations.
(i) at rest or constant speed
(ii) accelerates upward
(iii) accelerates downward
(iv) accelerates downward
at g (9.81 m/s2)
Example: If the system is in equilibrium, based on
the info from diagram, find (a) the tension forces FTA
and FTC, and (b) the mass mC.
d) Example: If the system is in equilibrium, based on
the info from diagram, find (a) the tension forces T1,
T2 and T3, and (b) the mass m.
e)
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Section:
Example: If the system is in equilibrium, 𝜃 = 30!
and m2 = 5 kg, based on the info from diagram, find
(a) the tension forces T, and (b) the mass m1.
Mr. Lin
b) Example: An 800N person measures his weight in
an elevator. If the elevator is accelerating upward at
2 m/s2, what will be reading on the scale?
c)
Example: A 10kg block is accelerated at 2 m/s2, as
shown in the diagram. Find (a) the tension T of the
rope, and (b) the mass m2.
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