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Lecture

chapter 4


Department
Astronomy & Astrophysics
Course Code
AST101H1
Professor
Clifford Orwin

Page:
of 3
chapter 4
Newtons 1st law---An object at rest remains at rest, and an object in motion remains in
motion at constant speed and in a straight line unless acted on by an unbalanced force.
eg. a bike laying on the ground flat stays like that unless an unbalanced force acts on it
( a person lifting the bike up) and a rolling bike will keep rolling and it will only stop
unless an unbalanced force acts on it. The combined friction from ground and air will
cause it to slow down. WITHOUT friction the bike would keep on going forever.
2nd law---The acceleration of an object depends on the mass of the object and the
amount of force applied.
acceleration=force/mass ( the larger the force, the larger the acceleration)
eg. a person pushing a bike with little force with just get the bike rolling
a person pushing a bike with maximum force with make the bike accelerate
!!!!BUT MASS ALSO PLAYS A ROLE
a person pushing a bike with a child riding=bike will move faster
a person pushing a bike with an adult riding=bike moving much slower
THESE BIKE RIDERS ALSO HAVE MOMENTUM
momentum=mass*velocity
NEWTONS 2ND LAW OF MOTION AFFECTS MOMENTUM BECUSE:
since an unbalanced force causes acceleration, which is a change in velocity, then force
also changes momentum
3rd law----Forces act in equal and opposing pairs
you push down on the ground when u walk and the ground pushes up towards your feet
3 basic terms on how an object is moving
1)Speed- how far a car will go in a certain time (100km/hr)
2)Velocity- both speed and time
3)Acceleration- if the speed or direction change (slowing speed or change in direction
is negative acceleration
Galileo- demonstrated that gravity accelerates all objects by the same amount
regardless of their mass
*air resistance causes difference in acceleration*
Acceleration of Gravity- acceleration of falling objects (g)
*Earth acceleration for falling objects is 10m/s*
www.notesolution.com
-An objects momentum is the product of its mass and velocity (momentum=mass*velocity)
-The only way to change momentum is to apply force
Angular momentum- object that is either spinning or moving along a curved path
Torque- force used to change an objects angular momentum (twisting force)
MASS AND WEIGHT
Mass- amount of matter in your body
weight- scale measurements also, depends on body mass and force(gravity) acting on
your mass
example: elevator
when standing in an elevator moving up your mass does not change but your weight
does by becoming heavier and when moving down you become lighter
example: #2
weight less on moon because gravity is weaker
Free-Fall- falling without any resistance to slow you down (consequently makes you
weightless)
-astronauts are in constant free fall
Newton systems of laws that govern all motion
-delivered the final blow to Aristotle"s physics
-Newton brought the heavens and earth together as one universe
Newtons laws of motion
1st law- objects remain in motion unless a force acts to stop them (An object at rest
remains at rest, and an object in motion remains in motion at constant speed and in a
straight line unless acted on by an unbalanced force.)
example: a bike laying on the ground flat stays like that unless an unbalanced force acts
on it ( a person lifting the bike up) and a rolling bike will keep rolling and it will only stop
unless an unbalanced force acts on it. The combined friction from ground and air will
cause it to slow down. WITHOUT friction the bike would keep on going forever.
2nd law- he acceleration of an object depends on the mass of the object and the
amount of force applied.
acceleration=force/mass ( the larger the force, the larger the acceleration)
example: a person pushing a bike with little force with just get the bike rolling
a person pushing a bike with maximum force with make the bike accelerate
!!!!BUT MASS ALSO PLAYS A ROLE
www.notesolution.com
a person pushing a bike with a child riding=bike will move faster
a person pushing a bike with an adult riding=bike moving much slower
3rd law-for any force, there is always an equal and opposite reaction force
example: you push down on the ground when u walk and the ground pushes up towards
your feet
www.notesolution.com