centripetal force and gravity 4/27/07. recap = s r = t = t s = r v t = r a t = r a c =...

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Centripetal Force and Gravity 4/27/07

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Centripetal Force and Gravity

4/27/07

Recap

= sr

= t

= t

s = r

vT = r

aT = r

ac =v2

r

ac = r2

Fc = mac = m v2

r

Fc = mac = mr2

= 2T

Recap (UCM)Uniform Circular Motion

UCM means that is constantWhich means that… = 0aT = 0|vT| = constant

BUT… vT is not constant because the direction changes

UCM

UCM

FSB

UCM

FSB

UCM

FSB

FSB

UCM

FSB

FSB

UCM

FSB

FSBFSB

UCM

FSB

FSBFSB

UCM

FSB

FSBFSB

FSB

Vertical UCM

Vertical UCM

FSB

Vertical UCM

FSB

mg

What’s keeping the ball pinned up against the top?

Vertical UCM

FSB

mg

What’s keeping the ball pinned up against the top?

Inertia

Vertical UCM

FSB

mg

Fc = F = FSB + mg

Fc is the sum of the inward forces on the ball.

Fc

Vertical UCM

FSB

mg

Fc = F = FSB + mg

Fc is the sum of the inward forces on the ball.

Fc

Fc = mr2 = m v2

r

Vertical UCM

FSB

mg

Fc = F = FSB + mg

Fc is the sum of the inward forces on the ball.

Fc

m = FSB + mg

Fc = mr2 = m v2

r

v2

r

Vertical UCM

Vertical UCM

FSB

mg

Fc is the sum of the inward forces on the ball.

Vertical UCM

FSB

mg

Fc is the sum of the inward forces on the ball.

Fc = F = …

Vertical UCM

FSB

mg

Fc is the sum of the inward forces on the ball.

Fc = F = FSB

Vertical UCM

Vertical UCM

FSB

Vertical UCM

FSB

mg

Vertical UCM

FSB

mg

Fc is the sum of the inward forces on the ball.

Fc = F =

Vertical UCM

FSB

mg

Fc is the sum of the inward forces on the ball.

Fc = F = FSB

Vertical UCM

FSB

mg

Fc is the sum of the inward forces on the ball.

Fc = F = FSB - mg

Vertical UCM

FSB

mg

Fc is the sum of the inward forces on the ball.

Fc = F = FSB - mg

Fc = mr2 = m v2

r

m = FSB - mgv2

r

Vertical UCM

Is the force of the string on the ball greater at the top or at the bottom?

Vertical UCM

FSB

mg

FSB

mgIs the force of the string on the ball greater at the top or at the bottom?

Vertical UCM

What is the slowest vT the ball can have if it doesn’t fall when it reaches the top?

Vertical UCM

What is the slowest vT the ball can have if it doesn’t fall when it reaches the top?

Happens when Fc just counters mg (I.e. FSB = 0)

Vertical UCM

What is the slowest vT the ball can have if it doesn’t fall when it reaches the top?

m = mgv2

r

Happens when Fc just counters mg (I.e. FSB = 0)

Vertical UCM

What is the slowest vT the ball can have if it doesn’t fall when it reaches the top?

m = mgv2

r

Happens when Fc just counters mg (I.e. FSB = 0)

= gv2

r

Vertical UCM

What is the slowest vT the ball can have if it doesn’t fall when it reaches the top?

m = mgv2

r

Happens when Fc just counters mg (I.e. FSB = 0)

= gv2

r v2 = rg

Vertical UCM

What is the slowest vT the ball can have if it doesn’t fall when it reaches the top?

m = mgv2

r

Happens when Fc just counters mg (I.e. FSB = 0)

= gv2

r v2 = rg

v = rg