#### Newton’s Laws of Force

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Transcript Newton’s Laws of Force

Gravity
Chapter 3 Section 2
Effects of Gravity
Why
does the apple fall down
from the tree and not float
around in space?
All objects have forces of
attraction between them
this force of attraction is called
gravity
Gravity
is the force of attraction
between objects and the Earth
the amount of gravitational
force between objects depends
on their masses and the distance
between them
Weight
The
force that is caused by
gravity. The mass and the
distance determine the weight.
Good test question
Do
you weigh more, less or the
same on the moon compared to
Earth?
The Third Law of Motion
Chapter 3 Section 3
Newton’s Third Law
Shooting
a gun
rowing a boat
rocket propulsion
ice skater pushing off
Newton’s
third law of motion
–when one object exerts a force on
a second object, the second one
exerts a force on the first that is
equal in size and opposite in
direction
–to every action force there is an
opposite and equal reaction force
How
is this law different from the
other two?
Forces don’t cancel each other out
even if they are equal and opposite.
There are always two objects
involved
If forces are equal then how can a
swimmer move through the water?
Newton’s second law determines
the acceleration of an object
The
forces are equal, but
the masses may not be
the objects with less mass
will accelerate more
Momentum
Why
is it harder to stop a
loaded train car verses an
unloaded train car?
Why is it harder to stop a train
car moving at 10 m/s verses a
train car moving at 5 m/s?
Momentum
is a property an
object has due to its mass and
velocity
can be calculated by
multiplying mass times velocity
momentum = mass x velocity
r = m x v
units are kgm/s
Force & Changing Momentum
How do you stop the baseball from stinging
your hand as you catch it?
Why to air bags work?
Newton’s 2nd law says F=ma
v f vi
And
a
t
So F m( v f vi )
t
Rearrange to have the equation
Ft=m(vf-vi) or Ft=mΔv
Where: Ft is called impulse
So the impulse equals the change in
momemtum
Momentum
has direction
momentum will change only if
its mass or velocity changes
momentum can be transferred
from one object to another
–pool balls
–car crashes
–hockey players
Law of Conservation of
Momentum
The
total amount of momentum
of a system does not change
unless an outside force acts on
the system
–pool balls