Transcript 1210thirdlaw.pdf

Newton’s Third Law
Newton’s Third Law of Motion
• Whenever one object exerts a force on a
second object, the second object exerts an
equal and opposite force on the first.
• “To every action there is an equal and
opposite reaction”
• F(AB) = - F(BA)
• Forces come in pairs. In nature there is no
single force (all by itself).
Examples
• I exert a force on a desk with my foot and the
desk exerts a force back on my foot. (“I kick a
desk and the desk kicks me back.”)
• A hammer exerts a force on a nail and the nail
exerts a force back on the hammer.
Force “on” and “by”
• A force influences the motion of an object
only when it is applied on that object. A force
exerted by a body does not influence that
body (itself); it only influences the OTHER
body on which it is exerted.
• F(AB) = - F(BA)
Group Activity
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1. Explain walking forward on East Bottom.
2. Explain birds flying south.
3. Explain a rocket lifting off Cape Canaveral.
4. A person throws a package out of a boat
(initially at rest).
• 5. A bat exerts a 50 N force on a baseball.
• 6. An inflated, but untied, balloon flies off.
• 7. Earth exerts gravitation on the moon.