Download Name: Gravity Notes In a car accident, a seat belt helps prevent

Name: _________________________
Gravity Notes

In a car accident, a seat belt helps prevent injuries by applying a force
(1) less than the force of the moving passenger
(2) greater than the force of the moving car
(3) in the same direction as the car’s motion
(4) in the opposite direction of the passenger’s motion
Gravity

Which falls fastest, a feather or a bowling ball?
GRAVITY AFFECTS THEM BOTH EQUALLY SO THEY FALL AT THE SAME RATE. AIR RESISTANCE
AFFECTS THE FEATHER MORE SO IT FALS SLOWER WHEN THERE IS AIR, BUT IN A VACCUUM (NO
AIR) THEY HIT THE GROUND AT THE SAME TIME

Newton’s Law of universal gravitation: all OBJECTS in the universe are ATTRACTED to each
other

Gravity is:

A FORCE OF ATTRACTION BETWEEN ALL OBJECTS IN THE UNIVERSE

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Why does an apple fall towards the earth instead of the earth towards the apple?
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Why THINGS ARE PULLED TO THE CENTER OF THE EARTH
THE EARTH HAS MUCH MORE MASS THAN THE APPLE AND THEREFORE MORE GRAVITY
Gravity depends on DISTANCE and MASS

LARGER masses exert MORE gravity

SMALLER masses still exert gravity (it is just hard to tell)

Force of gravity DECREASES as distance between objects INCREASES (AS THEY GET
FARTHER APART)

The force of gravitational attraction between two objects depends on the distance between the
objects and their
(1) buoyancies (3) masses
(2) temperatures (4) shapes

A battery-powered cart pulls an 800-gram load across the floor. If the load were reduced to 400
grams, and the force used to move the cart remained the same, the cart would
(1) move slower
(2) move faster
(3) move at the same speed
(4) stop moving

What force keeps the moon hanging around? GRAVITY

Orbits happen because an object’s FORWARD MOTION keeps it from falling straight down
(balance between forward motion and downward pull gives planets and satellites their
CIRCULAR paths)

Does the moon exert gravity on the earth? YES

How do we know? THE MOON PULLS THE OCEAN AND CAUSES TIDES

G FORCES refer to the amount of gravity experienced (1 G = normal pull of gravity; 9 G is max
humans can experience and survive)
Name: _______________________
Friction Notes

Why does the book stop?
FRICTION

Friction is a force that opposes (goes in the opposite
direction of) motion

Static friction: friction while not moving


Must be overcome for object to move
Sliding friction: friction while sliding

Makes things in motion slow/stop

Air resistance is friction in the air

What tire surface would you rather have?
ONE WITH TRACTION (BUMPS) RATHER THAN SMOOTH

Friction makes motion possible!

List things that would not be possible
without friction:

DRIVING, WALKING, RIDING A BIKE,
ETC.

What happens to motion when friction is decreased?

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Too much friction can be a bad thing—why?

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Heat, malfunction (things break)
Or too much friction on your feet?


CAN CAUSE HEAT OR MALFUNCTION (THINGS CAN WEAR OUT OR BREAK)
What if there is too much friction inside an engine?


MOTION INCREASES OR SPEEDS UP
Blisters 
How do you move things against friction?

You need to apply a force greater
than the friction force for
something to move

If you are wearing socks, are you more likely to slip on a carpeted floor or a polished linoleum
floor?


How can you change the amount of friction?


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POLISHED FLOOR (B/C LESS FRICTION)
CHANGE THE TEXTURE OR SURFACE SOMEHOW
Less friction:

Rolling friction (use rollers or wheels)

Lubricants
To have more friction:

Sand

Tread

Non-slip surfaces
Free fall & terminal velocity
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Another word for a thrown object?

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Projectile
Near the surface of the earth, acceleration due to gravity is about
10m/s2

That means for every second you fall, you speed up by 10
m/s (10 meters per second, per second)

Free fall occurs when gravity (weight) is the only
force acting on an object

The moon is in free fall

So is a skydiver

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Terminal velocity is the maximum speed an object
reaches while free falling

In terminal velocity, the force of gravity equals the air resistance, so there is no
acceleration (net force = 0)