conceptual physics

Conceptual PhysicsConceptual Physics

Notes on Chapter 10-11Notes on Chapter 10-11

Center of Gravity &Center of Gravity &

Rotational MechanicsRotational Mechanics

Center of Gravity &Center of Gravity &Rotational MechanicsRotational Mechanics

Every object will Every object will rotate about a rotate about a central point…central point…CENTER OF CENTER OF GRAVITYGRAVITY..

• Note: Also known Note: Also known as as CENTER OF CENTER OF MASSMASS


How to find the Center How to find the Center of Gravity (CG).of Gravity (CG).

• All of an objects mass All of an objects mass

actsacts as if it were as if it were concentrated at it’s concentrated at it’s center.center.

• If you suspend any If you suspend any object, then draw a line object, then draw a line beneath. Repeat until beneath. Repeat until you get two lines that you get two lines that cross. cross.


TopplingToppling• An object will An object will

topple over only topple over only when the CG when the CG extends beyond extends beyond the base of the base of support.support.


StabilityStability• The closer the The closer the

CG is to the CG is to the base (ground), base (ground), the more the more stable an stable an object is said object is said to be.to be.


Center of Gravity on PeopleCenter of Gravity on People


TORQUETORQUE• Torque is simply a turning force.Torque is simply a turning force.

Open a door knobOpen a door knob Tighten a nut with a wrenchTighten a nut with a wrench Using a Hammer.Using a Hammer.


A torque is produced when a force is applied A torque is produced when a force is applied with with LeverageLeverage..• Leverage is what is used to apply a force to an Leverage is what is used to apply a force to an

object.object.

This force is applied through the This force is applied through the LEVER ARMLEVER ARM..


TORQUETORQUE

• TORQUE TORQUE = = FORCEFORCE X X LEVER ARMLEVER ARM

So the same torque can be produced So the same torque can be produced by a large force and a short lever by a large force and a short lever arm … or small force with a large arm … or small force with a large lever arm.lever arm.


Ever try pull a nail with a small or Ever try pull a nail with a small or large hammer? Which is easier? large hammer? Which is easier? Why?Why?


Angular MomentumAngular Momentum• Angular Momentum is like Linear Momentum Angular Momentum is like Linear Momentum

– has a vector quantity and magnitude.– has a vector quantity and magnitude.

• Angular MomentumAngular Momentum = = Rotational inertiaRotational inertia xx Rotational velocityRotational velocity

• Angular MomentumAngular Momentum = = massmass xx velocityvelocity

• Angular Momentum Angular Momentum = = II ωω• Angular Momentum Angular Momentum = mvr= mvr


CONSERVATION OF ANGULAR MOMENTUMCONSERVATION OF ANGULAR MOMENTUM

If no unbalanced external If no unbalanced external torque acts on a rotating torque acts on a rotating system, the angular system, the angular momentum of that system is momentum of that system is constant.constant.

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