Transcript Forces and Motion

Forces and Motion
Chapter 2 – Gravity, Motion, and Light
Matter
• Anything that has ___________ and
takes up _________.
• All matter is composed of __________
• Atoms have several subatomic
particles.
– _________&_________ – In the nucleus
– __________ – Orbit around the nucleus
• All matter, and subsequently atoms,
are subject to four forces of Nature.
Forces of Nature
•
– The force of attraction that is
between two bodies and is generated by
their masses.
– More later
•
– The force arising between
electrically charged particles or between
charges of a magnetic field. (holds
electrons to the nucleus)
– More later
•
force – Only important on a
subatomic scale. Holds the protons to
the neutrons in the nucleus.
•
force – Only important at an
atomic scale and is responsible for
radioactive decay.
Gravity
• ______________gives the universe its
structure.
• It acts on _______ objects.
• Every particle is drawn toward every
other particle by its pull.
•
– The tendency for an object
at rest to remain at rest, and a body in
motion to remain in motion in a straight
line at a constant speed.
• Inertia was first demonstrated by
__________, but describe in to the law
we know today by _________________.
Newton’s first law of motion
• The ______________________.
• Objects at rest remain at rest unless
a force is acted upon it. Objects in
uniform motion continue moving in a
straight line unless other forces act
upon it.
• Newton’s first law explains how
_______________________________.
• Video
Determining the rate of drop
• Velocity is how fast an object is moving
in one direction.
• Velocity =
• V=d/t so
• T = d/v
• On Earth gravity causes objects to fall at
9.8 m/s2
• Notice that an objects mass has little to
do with its rate of fall in this example.
• However, an objects mass has a lot to do
with how quickly an object can accelerate
Newton’s second law of motion
Newton’s second law deals with a change in
direction or the acceleration of an object.
•
– A change in an object’s
velocity. (a deviation from uniform velocity).
– Acceleration can be positive - _____________
– Acceleration can be negative - _____________
– A change in direction is also a change in
acceleration.
•
– The amount of
acceleration that a force can produce, depends
on the mass of the object being accelerated.
The math behind Newton’s 2nd law
• __________ = object’s mass x acceleration.
• F = ma
• Force is measured in ____________, mass
in grams, and acceleration in meters/sec.
• Tomorrow, you will measure the amount of
force necessary to move two objects
across two different surfaces.
• Newton was able to deduce the law of
gravity using the moon’s motion and
applying his second law of motion.
The law of gravity
• Every mass exerts a force of
attraction on every other mass. The
strength of the force is directly
proportional to the product of the
masses divided by the square of
their separation.
• OR simply : _____________________
• G is a constant = 6.67x10-11
• We will not be calculating the force
of gravity between two objects
The effects of Gravity
• Gravity is the force that keeps us
“______________” to the Earth.
• It also keeps the __________ orbiting
around the Earth.
• The moon’s gravitational pull is
what causes the ____________.
– We will discuss the tides later in the
semester.
• Newton then used his first two laws
to state his third law : ________________________.
Newton’s third law of motion
• When two bodies interact, they
create equal and opposite force on
each other. See fig 2.8 in book.
• When I asked how would you return
to the space station with only a tool
box in your possession?
• We relied on Newton’s third law.
The force you applied to the tool box
was equal and opposite to the force
that the tool box applied on you,
thus it would force you to move in
the opposite direction.
Pulling g’s
• The term pulling g’s refers to the
gravitational attraction at a planet’s surface.
• Otherwise known as _____________
gravity.
• Surface gravity (g) is VERY important.
– It determines: your ______________
– The celestial body’s ______________
– The presence &/or the components of the
___________________
• The formula for determining surface gravity
is: g = GM/R2.
– G = constant 6.7x10-11
– M = The mass of the attracting body
– R = Radius of the attracting body
Determine your weight on the Moon
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Mass of the moon = 7.3x1022
Radius of the moon = 1.7x106
G= 6.7x10-11
Formula for g = GM/R2
The g on earth = 9.8
divide 9.8 by gmoon and that is how
many times different your weight is
on the moon than on earth
• Multiply your weight by that number
to get your lunar weight.
Escape velocity
•
• Escape velocity = √2GM/R
– G = constant (6.7x10-11)
– M= Mass of the body to be escaped from
– R= Radius of the body to be escaped from
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The escape velocity from the moon is 2.4 km/second
The escape velocity from the Earth is 11 km/second.
Why is it easier to escape the moon than Earth?
Does escape velocity have an effect on the ability of
a planet to sustain life?