For every action, there is an equal
but ________ reaction


Video Instruction





Show Me The Physics YouTube Channel





Visualizing Newton's 3rd Law

- Frank Noschese - John Jay H.S.



Action/Reaction - NASA
(right click, save as)









"Which way is

the skater below





"All the forces in the

universe, would  be:

a) an even number

b) odd c) unknowable









Even Number!!!







3rd Law of Motion


For every action
there is an equal but opposite reaction





"Press on a rock and the rock presses on you
(with an equal, but opposite force)"

- Newton




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[ HTML5 ]

Skateboarder 2

[ HTML5 ]





When object A exerts 
a force on object B,

Object B exerts
an equal force on A
but in the opposite direction




Forces Always
Come in Pairs



Collisions and 3rd Law

[ HTML5 ]
Show Me The Physics





A lamp applies a force of 10 N to a table.

What force does the table
 apply on the lamp?

Which direction is this force applied?

[ Flash ]










Earth pulls
down on you.


That's half the story...




You pull up on the earth.











Explain this phenomena using one or more
of Newton's Laws of Motion

Magnetically Coupled Pendula 2

School Blocks YouTube?
Use the file below.

Magnetically Coupled Pendula




The more active bouncing magnet applies a force on the slower magnet on the opposite side. By applying a force it receives a force and therefore slows down.







Paul Hewitt Question


A heavy rock and a light rock in free fall (zero air resistance) have the same acceleration. The reason the heavy rock doesn’t have a greater acceleration is that the

A. force due to gravity is the same on each. 

B. air resistance is always zero in free fall. 

C. inertia of both rocks is the same. 

D. ratio of force to mass is the same. 

E. None of these.




Isaac Newton



Rotational Inertia

St. Mary's U. Astronomy and Physics Dept.



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