Newton’s Third Law states that if two objects interact the force exerted on object 1 is equal in magnitude but opposite in direction to the force exerted on object 2 by object 1.

 Several forces are present when two objects interact with one another.  Body 1’s force on 2 is the action force and body 2’s on 1 is the reaction force.  The reaction force accelerates away from the earth and the action force accelerates towards the earth.    A normal force is also present which acts in both ways.

 The variables present are :

• Fg – the action force  (= to mg)
• Fg'  - the reaction force
• n-normal force exerting away from the earth
• n'- normal force exerting towards the earth
• Fg  ' = - Fg
• N=-n'

The stunt pictured is a QP.  The girl is standing on the guy’s single hand.  Notice the normal force present that holds her in the air.  In which direction are the action and reaction forces working?
 

THE SPORT OF GYMNASTICS AND CHEERLEADING:
A cheerleader must become an expert on the physics of rotation. When a she is thrown into the air for a fancy stunt that involves rotation of the body she has all the angular momentum from her push-off that she will get.
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• Angular momentum equals the product of mass, velocity and distance from mass to axis of rotation.
• QUESTION:How can her rate of rotation change without the help of someone giving her a little help or her pushing off on something?
• ANSWER: The angular speed increases or decreases by changing the distance between the mass and the axis of rotation. When a cheerleader performs a stunt, for example, a back tuck, she may have nothing to gain angular momentum(if she stands on the ground with velocity and position both equal to zero. But when she jumps up and tucks her mass in to decrease the distance between her body and the axis of spin.  Her angular momentum is still constant because no external torque (radius X force) occurs. Cheerleaders must be in top shape athletically and gymnastics background is often required to do the rigorous routines required today.

OTHER COMPONENTS OF PHYSICS INVOLVED IN CHEERLEADING INCLUDE:

FORCE
KINETIC ENERGY
ROTATIONAL KINETIC ENERGY
TENSION
POTENTIAL ENERGY
 TORQUE .....the list could keep on....but we'll stop here......
 
 

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