Announcements Tutorials this week Extra credit – due date Pre-AP – relativity discussion

Circular motion

Objectives Content SW understand the concept of inertia in circular motion. Language SW define centripetal force. SW Differentiate between centripetal and centrifugal force.

http://www.youtube.com/watch?v=hW57tLMcqt4 Linear Speed increases when the radius or the rotational speed increases.

If we swing a rock on a string over our head, what do we have to do to keep it in motion?

Centripetal Force http://www.youtube.com/watch?v=qsqpuRIwxoY

If we swing a rock on a string over our head, what do we have to do to keep it in motion? Pull inward

Centripetal Force A force is required to maintain circular motion Any force that causes an object to follow a circular path is called a centripetal force. Centripetal means “center-seeking”

It isn’t a new and mysterious force Gravitational force that holds the moon in orbit is a centripetal force

It isn’t a new and mysterious force Electrical forces holding the electrons in orbit around the nucleus are centripetal forces

Motion on a flat curve When a car rounds a corner, the _____and _____ provide the centripetal force tires road

If the tires are worn smooth, if the car is going very fast or the road is icy or oily, this friction force will not be available. The car will not be able to move in a circle, it will try to go in a straight line and possibly go off the road.

Highway Curves: Banked and Unbanked Car driving on a wall When a car goes around a curve, there must be a net force toward the center of the circle of which the curve is an arc. If the road is flat, that force is supplied by friction. Highway Curves: Banked and Unbanked

Highway Curves: Banked and Unbanked If the frictional force is insufficient, the car will tend to move more nearly in a straight line, as the skid marks show. Highway Curves: Banked and Unbanked

What would happen if an object were released from its orbit? Draw the direction it would travel if released at 1 and 2 1 2

The object would travel tangent to the circle in a straight line 1 2

Washing machines 1) The ___ rotates at high speed during the spin cycle 2) The tub’s _______ exert force on the clothes, but the holes prevent the tub exerting the same force on the ______. 3) _____ allows the water to escape in a straight line.

http://jalopnik.com/5415082/fifth-gear-brings-hot-wheels-to-life-sets-real+life-loop+the+loop-record

“Centrifugal Force” “Centrifugal force” is a fictitious force - it is not an interaction between 2 objects, and therefore not a real force. Nothing pulls an object away from the center of the circle.

“Centrifugal Force” What is erroneously attributed to “centrifugal force” is actually the action of the object’s inertia - whatever velocity it has (speed + direction) it wants to keep.

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