Phy Ch 5 Circular Forces Circular Motion Do

Phy Ch 5. Circular Forces

Circular Motion Do you see it? That tiny spark, that wee blip of light? It may not look like much, but it is in fact a normal planet orbiting a normal star, 250 trillion kilometers from Earth.

Newton said all objects move in a straight line unless acted upon by an outside force If an object exhibits circular motion, it is due to a centripetal outside force!!!

Read Only Revolving vs Rotating Small quiz: 1. The ball : 2. The hammer thrower: 3. Kids in seats: 4. The center of ride axel: 5. Earth on its axis : 6. Earth around sun

Circular Motion & Centripetal Force An object in motion remains in motion in a straight line and at a constant speed UNLESS acted upon by an EXTERNAL (unbalanced) Force. This is called a Centripetal Force! There are TWO conditions here : Condition #1 – The force pulls to the center of inferred circle Condition #2 – Inertia acts tangential to motion at any point What are the centripetal forces that act in this pic?

The Big 3 Circular Motion Equations

Rules 1. Angular velocity is not linear velocity V linear Fc 2. Linear velocity is changing b/c of direction 3. Radius is constant over set intervals a V Fc Fc 4. Net Force points inward V 5. Acceleration points inward with Net Force a linear

Fnet equations and FBD for Circ Mo A force applied in a straight line A force applied perpendicular to the motion F applied = FT = Ff = Fg= F E = F mag = …….

Visualizing a specific centripetal force Read Only A car traveling around a curve… . a) What centripetal force holds it on the curve? b) What direction is its force vector c) If the force was removed what would be the car’s path?

Core Problem 1. 0 What is the maximum velocity the car can go around the curve without sliding off ? Step 1 FBD Step 2 F net equation Fc = . = Step 3 Isolate and solve Knowns m= 200 kg m = 0. 50 r = 12 m vmax = ? v max a) If r went up, would v max go down?

What is Centrifugal Force Rotation vs Revolution

What is Centrifugal Force Latin (n) : center fleeing ! side view Top view F F F c centripetal centrifugall V linear q Inertia continues motion q Only 1 force is active in top or sideview q Centrifugal force is perceived, but not real

Chapter 7 Gravity

“Traveling through hyperspace ain’t like dustin’ crops boy” -Han Solo

Johannes Kepler (1571 -1630) Kepler developed three laws that describe the motions of the planets. #1 The law of ellipses. • The orbit of each planet is an ellipse with the sun as one of the foci. Not a circle!!!

#2 The Law of Equal Areas • An imaginary line from the sun to the planets sweeps out equal areas in equal time intervals Close to sun = faster Farther away = slower

#3 Law of Orbital Harmony • The ratio of the squares for the periods of two planets Is equal to the ratio of the cubes from their average distance from the sun!

Problem #1 The period of revolution for the earth is 1 year. Uranus takes 84 years to make its revolution around the sun. If Earth’s average distance from the sun is 149. 6 x 10 6 km, what would Uranus’ distance be?

3 2 (1 yr)2 (149. 6 x 10 6 ) 3 (84 yr)2 ( ra ) 3 2869356109 m

Newton marveled at the path of the moon around the earth…. he felt the moon “fell” into the earth….

Definition: any object that has mass in the universe exerts an attractive force on any other object with mass in our universe. The greater the mass, the greater the force; the greater the distance between objects -the weaker the force!!!

Match centripetal force with universal G equations 2 m 1= mass of 1 st object r = distance between objects m 2= mass of 2 nd object G= 6. 67 x 10 -11 N m 2 / kg 2

constant: G= 6. 67 x 10 -11 N 2 m / kg 2 Gravitaional “glue” between all things in universe, calculated by Cavendish!

The test:

The force of gravity is a shared force from the center of mass of two objects

Comparing the Fg of objects using r M r m 2 m Lets start here 1. F=______ m 2. F=______ = ___ M r 2 r 4. F=______ m 2 m 2 m F= 3. F=______ M ½r m 5. F=______

What if the object is a black hole ? It will have a mass 3 times higher than our sun It will fall out of our universe There is evidence one makes out galaxy spin It is so massive, light is pulled

Does the mass itself attract mass ? Einstein’s View of Universal Gravity Mass doesn’t attract mass with a particle High-precision test of general relativity by the Cassini space probe (artist's impression): radio signals sent between the Earth and the probe (green wave) are delayed by the warping of space and time (blue lines) due to the Sun's mass.

Match centripetal force with universal G equations 1. 2. m 3. v r M

Core Problem #1 a) Calculate the force that develops between a 1 x 10 9 kg mountain and the moon ( m= 7. 36 x 10 22 kg , r = 1. 74 x 10 13 m).

Core Problem #2 Calculate the average distance between the sun and the earth if the average force of attraction is 3. 5 x 10 22 N