Physics Unit 6B

Scenario: rubber stopper whirled on a string in a *horizontal* circle

Centripetal force: FT Net force equation: FT = mv^2/r

When a roller coaster car is at the *top* of the loop, the direction of the acceleration and net force is directed:

*downward*

An object traveling in a circle at a constant speed has what acceleration?

*inward* acceleration

Where on a roller coaster loop would a person feel lighter?

*top*: less FN than Fg (FN = 0)

When a roller coaster car is at the *bottom* of the loop, the direction of the acceleration and net force is directed:

*upward*

Two kids are on a merry-go-round, one is 2 m from the center, and the other is 3 m from the center. Which one has greater linear speed? Which one feels greater centripetal force?

3 m = greater *linear speed* because it has a *greater radius* 2 m = feels greater centripetal force because it feels more velocity the closer he is to the center

If you *triple* the *mass* attached to the end of the line without changing the rotating speed or radius, the force on the stopper will be...

3x the original force (*3m*v^2/r)

If you *triple* the *speed* attached to the end of the line without changing the mass or radius, the force on the stopper will be...

9x the original force (m*3^2*/r)

Explain how an object can be moving at a constant speed and still be accelerating when moving in a circle.

Because there is a change in velocity when an object *turns*

Scenario: car going around a curve on a flat street

Centripetal force: FK Net force equation: Fk = mv^2/r

Scenario: clothing spinning in a top-loading washing machine

Centripetal force: FN Net force equation: FN = mv^2/r

Scenario: rubber stopper whirled on a string in a *vertical* circle at *bottom* of its path

Centripetal force: FT Net force equation: FT - Fg = mv^2/r **FT > Fg

Scenario: rubber stopper whirled on a string in a *vertical* circle at *top* of its path

Centripetal force: FT Net force equation: Fg + FT = mv^2/r **FT < Fg

Scenario: rider spinning on a Ferris wheel at the *bottom* of the ride

Centripetal force: Fg, FN Net force equation: *FN* - Fg mv^2/r

Scenario: rider spinning on a Ferris wheel at the *top* of the ride

Centripetal force: Fg, FN Net force equation: Fg - *FN* = mv^2/r

Scenario: you are a rider on a merry-go-round but you are not holding onto the rail

Centripetal force: Fs Net force equation: Fs = mv^2/r

Magnitude of FN compared to Fg at *top* of loop of a rollercoaster (upside down!)

FN < Fg (FN = 0) -- feel lighter

Magnitude of FN compared to Fg at *bottom* of a Ferris wheel

FN > Fg -- feel *heavier*

Why did the rubber stopper in the lab move in a circle?

FT (force tension) pulling the stopper inwards

Why does an object moving in a circle accelerate towards the center?

Fc (net force) pulls it to the center

Magnitude of FN compared to Fg at *top* of a Ferris wheel

Fg > FN -- feel *lighter*

Magnitude of FN compared to Fg at *bottom* of loop of a rollercoaster:

Fg > FN -- feel heavier

Why are highways banked at a curve?

Gives you a "back up" centripetal force (FN) & pushes you back to the road

Explain why the last person "flies off" the chain so easily as he rounds the turn when ice skating?

He covers more distance = larger radius = Fc is less

The sticking to the wall phenomenon while on a barrel ride at an amusement park is best explained by the fact that:

The person has a natural tendency to move *tangent* to the circle but the wall (*FN*) pushes him inwards (*centripetal force*)

Suppose you are a driver in a car and you travel over the top of a hill in the road at a high speed. As you reach the crest of the hill, you feel your body moving upward as if there is an upward push on your body. This upward sensation is best explained by:

The tendency of your body to follow its original path upward (*inertia*)

What does slope represent on a v^2/r graph?

acceleration

What is a centrifugal force?

an outward force that *does not exist* -- it is inertia that makes you go straight

If you cut the *radius* by *1/3* without changing the mass or speed of the stopper, the force on the stopper will be...

x3 the original force (v^2/*3r*)