1. GRAVITY:
Ch 12.
Sec. 2
pages
GRAVITY IS EVERYWHERE!

2. 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…)

3. 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

4. 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.

5. 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.

6. 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.
sea level: m/s2
sea level: m/s2
 ~0.5% more force

7. 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.

8. NECAP QUESTION
2009

9. 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

10. 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 SAME RATE
Mass= 60kg
Mass= 60kg

11. (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)

12. 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.

13. 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

15. 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

16. 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

17. 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?!

18. FALLING PENNIES

19. 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

20. 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

21. 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.

22. 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.

23. 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

27. 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

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

29. ZERO GRAVITY CLASSROOM…