Transcript Motion Notes

Motion Notes
Speed
Momentum
Acceleration and Force
Friction and Air Resistance
Newton’s Laws of Motion
I. Motion

A. Speed and Velocity.

1. Speed: the distance traveled divided by the
time interval during which the motion occurred.
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Since speed is a derived measurement.
 SI unit is meter per second (m/s).
When a car is moving at a speed that does not change
over a period of time, it is called constant speed.

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2. Speed can be determined from a distance-time
graph
3. Speed can be calculated using distance and time.

The equation for speed is:

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speed = distance/time
v=d/t
Velocity: is the quantity describing both speed and
direction. (Direction is the path of the motion: east, north, south,
etc…)

The equation for velocity is the same as speed, the
only difference is that you must indicate the direction of
the motion.
II. Momentum
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A. Momentum: a quantity defined as the
product of an object’s mass and its velocity.
(“power”).
B. Momentum equation:
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momentum = mass X velocity
p=mXv
(p= momentum, m= mass, v = velocity)
C. The law of conservation of momentum:

The total amount of momentum in a system is
conserved
III. Acceleration
A. Def: Change in velocity divided
by the time interval in which the
change occurred. (How fast an
object speeds up or slows down)
B. Key points:

1. A change in direction will result in
experiencing acceleration.
 2. Units are m/s2
Acceleration= final velocity-initial velocity
time
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3. Acceleration- indicates how fast a car is speeding up, or
how fast is slowing down
4. Positive acceleration means an object is speeding up.
5. Negative acceleration means an object is slowing down.

Ex. A car has a constant speed of 60 m/s and the person
driving the car increases his speed to 100 m/s. If it takes him
7sec to reach this speed, what is his acceleration in m/s2 ?
Formula: a= Vf-Vi
t

Ex. A car can go from 0 to 96 m/s in 4 sec, what is its
acceleration?
IV. Force
Force

A. Def: the cause of acceleration, or
change in an objects velocity.

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Net force: is the combination of all the forces
acting on an object.
Balance forces: forces acting on an object that
combine to produce a net force equal to zero.
Unbalanced forces: forces acting on an
object that combine to produce a
net nonzero force.
V. Friction and Air Resistance
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A. Friction: the force between two objects in contact
that opposes the motion of either object.
B. Air Resistance: a form of friction, it is caused by
the interaction between the surface of a moving
object and the air molecules.

What determines it amount of air resistance?
 1. Size
 2. Shape
 3. Speed.

Note: air resistance increases with as the objects speed increases.
VI. Gravity

A. Def: the attraction between two
particles of matter due to their mass.

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Gravity is a unique force; it does not have to
be touching the object to exert its force.
B. Mass and distance affect gravitational
force.

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1. As the distance between two objects
increases the gravitational force decreases,
and vice-versa.
2. The force of gravity is proportional to their
mass and inversely proportional to the square
of the distance between them.
Newton’s Laws of Motion
Newton’s First Law

Newton’s 1st Law:
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An object at rest tends to stay at rest and an
object in motion tends to stay in motion with the
same speed and in the same direction unless
acted upon by an unbalanced force.
Inertia: is the tendency of an object to remain at
rest or in motion with a constant velocity.
Newton’s 2nd Law

Newton’s 2nd Law:
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The force of an object equals its mass times its
acceleration.
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The unit for force is Newton (N).
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F=m X a
1N=1kg X 1m/s2
Practice problem:
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What is the force necessary to accelerate a 1250 kg
car at a rate of 40m/s2?
Free Fall and Weight

Def: the motion of a body when only the force of gravity
is acting on it.
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Free-fall acceleration near Earth’s surface is constant.
Note: in
this class we will disregard air resistance for all calculations.
Gravity acceleration on any object is 9.8 m/s2.
Weight equals mass times free-fall acceleration
 weight=mass x free-fall acceleration
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
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w=m X g
Weight is the force on an object due to gravity. Because weight
is a force, the SI unit of weight is the Newton (N).
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Weight is different from mass
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a. mass is a measure of the amount of
matter in an object
b. weight is the gravitational force an
object experiences due to its mass.
 Ex: 66 kg x 9.8 m/s2=650 N (Earth 150
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lb)
66 kg x 1.6 m/s2 = 110 N (moon 24 lb)
Weight influences shape
Terminal Velocity: the maximum
velocity reached by a falling object
that occurs when the resistance of
the medium is equal to the force of
gravity.
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The object has stopped accelerating at
this point.
Newton’s Third Law
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Newton’s Third Law: for every action force,
there is an equal and opposite reaction force.

Ex. When you kick a soccer ball, the force exerted
by your foot is the action force, the ball also
exerts a force on your foot, this is the reaction
force that is equal to the action force.