# Force push or pull

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posted:
3/23/2011
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```							          _____ – push or ____
• Sometimes ______
forces are obvious but
not always
•   can cause the ______
of an object to
change
•   force of moving ball
causes ball at rest to
move in the _______
of the force
Forces
• ___ force – 2 or more
forces acting on a
object @ same ____
•   zero because the ___
forces cancel each
other
•   Forces ____ in size &
_______ in direction –
balanced forces
________ forces
• 2 students pushing with
________ forces in
opposite directions – net
force occurs in the
direction of the _______
force
•   net force – will be the
__________ between the
two forces because they
are in opposite ________
Unbalanced forces
• forces are combined
(______ together)
because they are
exerted on the box in
the _______ direction
•   net force that acts on
this box – found by
_______ the two
forces together
Inertia – tendency of an object to
_______ any change in its motion
• If object is _______, it will have uniform
motion
• It will keep moving at the same _____ &
in same ________ unless acted on by an
unbalanced force
• velocity of the object remains _______
unless a force changes it
• object at ______ remains at rest
Inertia

• inertia of an object is related to its mass –
greater the ____ of object the greater its
inertia
• Sir Isaac ______ – stated rules that
describe the effects of forces on the
_______ of objects – known as Newton's
law's of motion
Newton’s ______ Law of Motion

• Also called the law of _______
• states that an object moving at a constant
velocity keeps moving at that _______
unless acted on by an unbalanced net
force
• object at rest stays at ____ unless acted
on by an unbalanced net force
law of inertia – explains what
happens in a car crash
50 km/h collides
something solid, the
car crumples, slows
down, and stops in
law of inertia – explains what
happens in a car crash
• Any passenger not wearing a safety belt
continues to move _______ at the same
speed the car was traveling
• Within about 0.02 s after the car stops,
unbelted passengers slam into the
dashboard, steering wheel, windshield, or
the backs of the front seats
law of inertia – explains what
happens in a car crash
• force needed to slow a person from 50
km/h to zero in 0.1 s is equal to 14 times
the force that gravity exerts on the person
• belt loosens a little as it restrains the
person, increasing the time it takes to
slow the person down
• this reduces force exerted on the person
• safety belt also prevents the person from
being thrown out of the car

```
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