Transcript Newtons laws

SEISMIC SLEUTHS Part 1
Newton’s Laws
EARTHQUAKES AND
PHYSICS?
•
Newton’s laws
•
Liquefaction lab
•
Smart Sitting
•
Energy and Quakes
CAN BUILDINGS BE MADE
SAFER?
• Building Fun
• Structural Reinforcement
• BOSS
• Earthquake in a Box
• Building Challenge
• Find and Fix the Hazards
• Strengthening your
House
Newton’s Laws of Motion:
• 1st Law: Law of Inertia
• Objects keep on doing what they are
doing.
http://www.physicsclassroom.com/mmedia/newtlaws/cci.cfm
Mass is directly related to inertia.
• The greater the mass the greater the tendency
to resist change of an object’s motion.
• objects will continue to do as they are doing with
out friction.
Equilibrium: if the net force on an object is zero
(at rest or moving at a constant velocity)
Static friction
• Static friction results
when the surfaces of
two objects are at rest
relative to one
another
2nd law: Net force: something that disturbs an
object’s equilibrium (net force changes an object’s velocity or
acceleration)
• Need to be able to
find the net force
(sum of all forces on
an object) since net
force causes an
object’s acceleration
http://www.physicsclassroom.com/mmedia/kinema/avd.cfm
2nd Law: acceleration of an object is proportional
to the mass of the object being accelerated
• F=ma
– a is in m/s/s
– m is in kg,
– F is kgxm/s/s or
Newtons
• F = mg (weight)
– Gravity (9.8 m/s/s)
http://www.physicsclassroom.com/mmedia/newtlaws/efar.cfm
Unbalanced force
• The normal force is
cancelled by the force of
gravity.
• The book is sliding to the
right but there is no force
in that direction.
• Because SLIDING friction
is currently the only
horizontal force it will
cause the book to come
to a stop
Sliding Friction
• If a car slams on its
brakes and skids to a
stop (without antilock
brakes), there is a
sliding friction force
exerted upon the car
tires by the roadway
surface.
Causes of friction:
• When the high points of each surface touch they bond,
you must break these bonds to move one of the pieces
(origin of static friction)
• As surfaces move across each other, electrostatic forces
continue to attract between high points, resulting in the
weaker kinetic friction
• Air drag (any fluid) depends on speed of the motion
(getting larger as speed increases)
• size and shape of object
• density of fluid
Forces
• (Ff) Friction Force: The
contact force that acts to
oppose sliding motion
between surfaces.
Parallel to the surface
Opposite the direction of
sliding
• Normal force (FN): The
contact force exerted by a
surface on an object.
Perpendicular to and
away from the
acceleration of the object
barring any resistive
forces.
3rd law:
• For every action there is an equal and opposite
reaction
http://www.physicsclassroom.com/mmedia/momentum/crete.cfm