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Gravity
Because the earth is so large ALL objects are pulled towards it.
Objects fall towards the earth at the same rate (acceleration).
Acceleration due to gravity is 9.8 m/s2 for ALL objects.
Air resistance slows down the speed of a falling object.
Because the air particles have mass, they have Inertia.
The amount of air resistance depends on the size and shape
of the object falling.
Free Fall – When only gravity is acting on an object, no other
forces are involved.
Orbiting – An object is pulled towards the center by gravity.
The object also has forward velocity. Combined
they equal the orbit of an object.
Centripetal Force – “towards the center”. In an orbit, it is
gravity.
Projectile Motion – Similar to an orbit, it is the curved path
that an object in flight follows.
Projectile motion has two components, Horizontal and Vertical
Horizontal motion is side to side and
is constant, except for air resistance
Vertical motion is changing due to
gravity. All objects are pulled down.
We must look at each component separately and then
combine them.
Ex. A ball rolling across a table has a horizontal component
only, no vertical component. Once it hits the edge of the
table, now it has a vertical component.
White Ball
Vert – 9.8 m/s
Hor – 0 m/s
Gray Ball
Vert - 9.8 m/s
Hor – 3 m/s
Vert – 19.6 m/s
Hor – 0 m/s
Vert - 19.6 m/s
Hor – 3 m/s
Vert – 27.4 m/s
Hor – 0 m/s
Vert - 27.4 m/s
Hor – 3 m/s
Newtons Laws of Motion
1st Law – An object at rest remains at rest and an object in
motion remains in motion at a constant speed and a straight
line unless acted on by an unbalanced force. (think inertia).
2nd Law – The acceleration of an object depends on the mass
of the object and the amount of force applied to that object.


Acceleration decreases as mass increases.
Acceleration decreases as force decreases.
Reminder we measure force in Newtons. 1N = 1
kg m
/s2
Formula
Force = mass x acceleration
100 kg
F = ma
F = ma
5N = 100kg (a)
5N
5N_
100kg
=.05 m/s2
100 kg
a = 10 m/s2
F = ma
F = 100kg (10 m/s2)
= 1,000N
3rd Law – When one object exerts a force on a second
object, the second objects exerts an equal and opposite
force on the first. (Forces always act in pairs).
Action = Reaction (forces in pairs)
Momentum – is like inertia, it is the mass x velocity
The more mass or velocity it has, the more momentum it has.
Ex. Bowling ball (catching or throwing)
Formula
Momentum = Mass x Velocity
P=mxv
Transfer of momentum – momentum moves from one
object to another.
Before
After
Before
After
Conservation of Momentum – When two objects collide,
they can change or exchange momentum, but the total
momentum, stays the same.
Momentum before the collision = Momentum after the collision
BEFORE
10 m/s
0 m /s
0 m /s
50 m/s
50kg
50kg
10kg
500
10kg
/s + 0 kg m/s
= 500 kg m/s
kg m
AFTER
0
/s + 500 kg m/s
= 500 kg m/s
kg m
BEFORE
5 m /s
0 m /s
0 m /s
50 m/s
50kg
50kg
50kg
250
50kg
/s + 0 kg m/s
= 250 kg m/s
kg m
AFTER
0
/s + 250 kg m/s
= 250 kg m/s
kg m
BEFORE
10 m/s
0 m /s
5 m /s
25 m/s
50kg
50kg
10kg
500
10kg
/s + 0 kg m/s
= 500 kg m/s
kg m
AFTER
250
/s + 250
= 500 kg m/s
kg m
kg m
/s