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Motion
•Position = location
•Motion = Event that involves a change in the position or location of something
•Distance is the total length traveled from motion…distance traveled depends on the path you take
•Displacement is a straight line distance between 2 points
•Reference point is a location to which you compare other locations
•Change in position tells us that motion took place but doesn’t tell us how quickly happened
Types of Motion
• Uniform motion - constant speed in a straight line
• Accelerated motion – motion that is changing in
speed or direction
• Circular motion - speed is constant but the
direction of motion is changing continuously
Speed
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Speed = the distance something moves in a given amount of time
Speed is a rate; rates are when you compare a change in one quantity to another
quantity
The greater the speed, the faster it changes position
To calculate speed, you need distance and time measurements; s = d/t
The standard unit for speed is meters per second m/s
Speed is not constant
Your speed at any given moment is your instantaneous speed…how fast
something is moving at a particular instance in time
Average speed = total distance traveled / total time elapsed
Constant Speed = speed that doesn’t change
Velocity
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• Velocity is speed in a certain direction…units are m/s
too!
• Vector – has magnitude (speed) and direction. Velocity is a vector.
• Speed is a scalar quantity…it only has magnitude
Acceleration
Velocity = distance / time
(remember velocity is a vector)
Acceleration = Vfinal – Vinitial
Time
NBC Science
of Football
• Acceleration is the rate in which velocity changes with time,
its not the same as velocity
• It is any change in velocity…when you come to a stop or turn
you are accelerating
• Units of acceleration are expressed in m/s2 because it is
velocity (m/s) divided by time (s)
• Free fall is an object in motion solely under the influence of
gravity…9.8m/s2…which means every second speed increases
by 9.8 m/s
Relative
Motion
Animations
• How an observer sees motion depends on how it compares with
their motion… is called relative motion
• Relative Motion – it is described and compared to a REFERENCE
POINT
• Motion is described by using a frame of reference
• Look at the picture of the planes above, which is moving?
Force
• Force is a push or pull on an object In a particular direction…forces are
used everyday to change the motion of objects; Forces cause changes in
speed and direction (velocity) and acceleration
• Contact forces are those that push or pull an object by touching it
• Action-at-a-distance forces are another type of force like gravity,
electrical force between two charges, and magnetic force
• Forces usually act in pairs
• Forces usually can’t be seen, but their effects can
• Gravity is the force of attraction between two masses…the earth’s
gravity pulls on us
How Can Forces Affect Objects?
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Slow them down
Speed them up
Change their direction
Change their
shape…squeeze and tear
Force
Animations
• Like Velocity, Force is a vector…it has ? And ? To get a car from point a
to point b, force must be applied in the right direction
• Net force is the overall force acting on an object when all other forces
are combined…if net force = 0 then the force acting on the object is
balanced
• Balanced forces have the same effect of no force at all
• Unbalanced forces are needed to change an object’s direction/motion
• When two forces act in the same direction the net force is the sum of
the two forces; when unequal forces act in opposite directions the net
force is the difference of the two
• The final force and direction is called the resultant force
• The unit for force is the NEWTON which is equal to kg*m/s2
Newton’s Three Laws
• Sir Isaac Newton helped develop three laws to
describe motion that are still in use today
• Newton’s ideas were built upon those of Galileo Galilee
• Galileo concluded that in the absence of friction, a
moving object will continue to move, even if there is no
force acting on it…friction stops objects in motion
Newton's 1st Law = Law of Inertia
• Objects at rest stay at rest and those moving stay moving unless there
is a force acting on them…Newton’s 1st Law (Law of Inertia)
• Inertia is a resistance of an object to a change in the speed or
direction of its motion…Newton’s First Law is also known as the
law of inertia
• Inertia is closely related to mass…when you measure mass you
are also measuring its inertia…it is easier to push a Hyundai than
a Mac truck…it is harder to change the motion of an object with
more mass…the more mass, the more inertia
• Slamming on the breaks in a car is an example of our inertia
overcoming the force of friction on the seats
Animations
nd
Newton's 2 Law
• If you are to give 2 objects of different masses the same
acceleration, different forces need to be applied
• Newton’s 2nd Law states that the acceleration of an object
increases with increased force. Acceleration also goes up
with decreasing mass…the direction of acceleration is the
same as the force
• In other words, if you wanted to give two different masses
different accelerations you would need to apply different
forces to them
F = ma
M = F/a
a = F/m
http://www.myphysicslab.com/pendulum1.html
• Force = mass x acceleration
• To use this you need to understand the
units for force are called Newtons (N)
• A Newton is the amount of force needed to
accelerate 1 kg of mass one meter per
second (1 m/s2)…1 kg x m/s2
Newton’s Third Law
Force
• Every action has an equal and opposite reaction = Newton’s 3rd Law
• When you stub your toe, the same force is exerted back on you as you
put in
• Your chair resists the force of your body with the same push
• Describes why forces act in pairs
• Action and reaction forces are equal forces acting in opposite directions
on different objects
Friction
• Friction is a force that resists motion between two surfaces that are
pressed together. The direction of friction force is always in a
direction opposing motion
• Although friction can make some tasks more difficult, most activities,
like walking, would be impossible without it
• Many surfaces appear to be smooth, but when magnified, have bumps
and ridges
• The type of surface, motion of the surface, and force pressing the
surface together all determine the friction between objects
• Friction also produces heat
• Friction created in a fluid is called drag
• Friction due to the air is called air resistance
Centripetal Force
• Centripetal force is any
force that keeps an
object moving in a circle
• The force points toward
the center of the circle
• The faster an object
spins, the greater the
acceleration, the greater
the acceleration, the
greater the force
• Likewise, the more
massive an object, the
more force required to
keep it moving at the
same speed as a less
massive one
• The opposite,
centrifugal force, is an
outward force away
from the center of
rotation
Momentu
m
• Momentum is a measure of mass
in motion…the momentum of an
object is the product of its mass
and its velocity
• At the same velocity, a semitruck has more momentum than a
Scooter
• You can increase momentum by
increasing velocity
• Is similar to inertia; both depend
on mass
• Dissimilar in that momentum has
velocity
• Momentum = mass x velocity;
or p = mv
• Momentum is a vector
• Conservation of momentum
states that in the absence of an
external force, the momentum of
an object remains unchanged
• A collision is a situation in which
two objects in close contact
exchange energy and
momentum…momentum is
conserved in these collisions