Transcript Gravity - ScienceRocks8

Key Concepts
• What factors affect the gravitational
force between two objects?
•
Why do objects accelerate during
freefall?







Gravity
Mass
Weight
Free fall
Air resistance
Terminal velocity
projectile

Sir Isaac Newton concluded
that a force acts to pull
objects straight down
toward the center of the
Earth

Gravity is a force that pulls
objects toward each other

The force of gravity
acts between all
objects in the
universe

Any 2 objects in the
universe attract
each other



Two factors affect the
gravitational attraction
between objects: mass and
distance
Mass - a measure of the
amount of matter in an
object (atoms)
SI unit of mass is kilogram - 1
kilogram is the mass of about
400 pennies = 2.2 pounds



Mass – more mass an object has, the greater
its gravitational force
The sun’s mass is so great that it exerts a
large gravitational force on the planets – One
reason why they stay in orbit
Distance – the farther apart two objects are,
the less gravitational force between them




Mass is the measure of the
amount of matter in an
object
Weight is a measure of the
gravitational force exerted
on an object
Weight varies with the
strength of the
gravitational force, but
mass does not
Mass weight gizmo


Free fall –occurs when gravity is the only
force acting on an object
An object in free fall is accelerating because
the force of gravity is an unbalanced force



Near the surface of the Earth the acceleration
due to gravity is 9.8m/s2
For every second an object is falling its speed
increases by 9.8 m/s
All objects in free fall accelerate at the same
rate




Objects falling through air experience a type
of fluid friction called air resistance
Friction is a force in the opposite direction of
motion so air resistance is an upward force
Falling objects with greater surface area
experience more air resistance
In a vacuum there is no air, all objects fall at
the same rate of acceleration





Air resistance increases with velocity
Eventually the falling object will fall fast
enough that the upward force of air
resistance will equal the downward force of
gravity
At this point, the forces are balanced and the
objects stops accelerating
The object continues to fall at constant speed
This is called terminal velocity – when the
force of air resistance = weight of the object

Projectile - An object that is thrown

Will an object that is thrown horizontally
land on the ground at the same time as an
object that is dropped?

The force of gravity still acts on the object in
the same way. It falls downward at the same
rate of acceleration as a ball that has been
dropped



If you throw an object at an upward angle,
the force of gravity will reduce its vertical
velocity until it stops.
Then the force of gravity will pull it back to
the ground
When it falls it will accelerate at 9.8m/s2
 Goalfinder









http://www.aps.org/publications/apsnews/200510/zerogravity.cfm
http://www.williamsclass.com/EighthScienceWork/ImagesEighth/
gravityEarthPull.gif
http://learn.uci.edu/media/OC08/11004/OC0811004_L6GravityFor
ce.jpg
http://www.melancholyrhino.com/images/gravity.jpg
http://imagine.gsfc.nasa.gov/YBA/M31velocity/images/twomass.gif
http://www.daviddarling.info/encyclopedia/W/weight.html
http://www.bkpc.co.uk/freefall.jpg
http://leedsmathgeeks.com/wpcontent/uploads/2009/02/terminal_velocity.gif
http://www.mredwards.net/images/ProjectileMotion.GIF