GRAVITY: Ch 12. Sec. 2 pages 403-410 GRAVITY IS EVERYWHERE!

Minute Physics: What is gravity? A. GRAVITY Minute Physics: What is gravity? = The FORCE of ATTRACTION between ANY two objects All matter (anything that has mass) has gravity…but it’s only noticeable between massive objects (like planets…)

Ex: Earth vs. moon Mass of the objects The size of this gravitational force depends on 2 factors: Mass of the objects 1. __________________________ *As mass increases, the force of gravity increases Ex: Earth vs. moon

Distance between the objects 2. _________________________________ *As distance between the two objects _________, the force of gravity _________. increases decreases This is why we’re “stuck” to the surface of the Earth instead of being pulled off towards the more-massive sun.

Gravity & Tides Alternating rise and fall in sea level with respect to the land Caused by gravitational forces of Sun & Moon The moon has about a 70% effect on our tides. The Sun has a 30% effect. The sun’s gravity is stronger (179x stronger than the moon), but it’s far away.

Earth is a bit wider at the waist… The rotation (spinning) of the Earth creates the equatorial “bulge” The Earth’s diameter at the equator is 27 miles more than the pole to pole diameter At the poles closer to the center of the Earth  weigh slightly more. Poles @ sea level: 9.780 m/s2 Equator @ sea level: 9.832 m/s2  ~0.5% more force

Law of Universal Gravitation All objects in the universe attract each other through the force of gravity. As distance increases, force decreases. As mass increases, force increases.

NECAP QUESTION 2009

B. Weight vs. Mass 1. MASS The amount of _________ in an object that _______ changes. Measured in ___ MATTER NEVER kg 2. WEIGHT The gravitational ________ that an object experiences because of its _______. Weight= mass x gravity FORCE MASS Varies (changes) by location

ALL OBJECTS ACC. @ SAME RATE Weight is a FORCE. F = ______________ mass x acceleration So if weight is a force, we could replace F with mxg (weight) mxg=mxa (where m cancels out and g=a or ALL OBJECTS ACC. @ SAME RATE Mass= 60kg Mass= 60kg

(i.e. every object accelerates towards Earth 9.8 m/s per second) Acceleration of free-falling objects VELOCITY 1. All falling objects accelerate (change ____________) towards the _________ of the Earth due to __________ CENTER GRAVITY the acceleration of a falling object due to gravity (on Earth) is a constant = g= 9.8 m/s2 or 9.8 m/s/s (i.e. every object accelerates towards Earth 9.8 m/s per second)

Wait a minute… 9.8m/s2 down is NOT gravity!!! It is the acceleration DUE TO GRAVITY Gravity is a force of attraction. 9.8m/s2 down is the acceleration caused when gravity is the only force acting on the object.

Misconceptions about Falling Objects This means that the velocity of a freely-falling object __________ by ____ m/s for every _______ that passes (up to a certain point…) 9.8 INCREASES SECOND But…on Earth, not all falling objects hit the ground at the same time because of _____________ or _______________. FLUID FRICTION air resistance Misconceptions about Falling Objects

Hammer & Feather Drop on Moon (Apollo 15) On the moon…all objects hit the surface at the SAME time because there is no ____ on the moon. There IS GRAVITY. Gravity = ____ of Earth. AIR 1/6 Hammer & Feather Drop on Moon (Apollo 15) Water Balloon Fight in Space Force of G on Moon = 1.63 m/s/s

D. Terminal Velocity -shape -size -weight The __________ speed that an object can have in freefall due to ___________________. MAXIMUM AIR RESISTANCE Terminal velocity changes depending on the object’s -shape -size -weight

As objects fall, _____________ increases until it balances the _______ of the object FLUID FRICTION WEIGHT Physics of Sky Diving & Terminal Velocity Therefore, a heavier object will accelerate for a _________ time period and have a __________ terminal velocity. GREATER GREATER Flying Squirrel Suits?!

FALLING PENNIES

Falling Objects Lab Recap/Review Golf Ball Ping pong Ball Ping Pong & Golf Ball A ping pong ball reaches its terminal velocity first A golf ball continues to accelerate for a greater time period and has a greater terminal velocity- so it hits the ground first. Drag Weight

Penny in Middle & Penny on Side Index card with penny on side fell vertically (penny tipped card) SHAPE CHANGED This caused there to be less air resistance on the card Reaches terminal velocity later Accelerated for a longer time period & hit ground first DURING FALL BEFORE FALL

Magazine & Piece of Paper A flat sheet of paper falls slowly because of air resistance -it reaches its TERMINAL VELOCITY right away. Weight Air Resistance If placed on a magazine, the paper accelerates with the magazine. Since the magazine weighs more, it accelerates for a longer time period.

FALLING CATS -There are cats on record that have survived falls of over 32 stories (~320 feet). -They are more likely to die in falls less than 5 stories. HOW IS THIS POSSIBLE? -On average, cats reach their terminal velocity (60 mph) after falling about 5 stories. - Once reaching this velocity, they relax and spread out like a parachute, minimizing injuries.

E. Projectile Motion: CURVED Motion that has two components (horizontal & vertical) that combine to form a __________ path CURVED The two motions DO NOT affect each other

Why do astronauts feel weightless? Gravity in Space Why do astronauts feel weightless? In ISS, the space craft is “falling” towards Earth and gravity is about the same as on Earth (~90%) BUT the spacecraft is also moving sideways so the ISS does get any closer to E surface. Guns in Space?! Astronauts “float” when inside an orbiting spaceship because they are _______________! in FREE FALL

PARABOLIC FLIGHTS…experience “weightlessness” as you free fall with a plane….. only $2,950 per person!

ZERO GRAVITY CLASSROOM…