Unit 3 Notes

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Transcript Unit 3 Notes

Amusement Park Forces
What is a Force?
FORCE = Any push or pull which causes
something to change its speed or
What is a Force?
Balanced forces are equal in size
(magnitude) and opposite in direction
Balanced forces are not equal in size
(magnitude) and/or opposite in direction.
If the forces on an object are
UNBALANCED, we say a NET force
Amusement Park Forces
What is a Force?
Can you think of examples of forces?
Balanced Forces?
Unbalanced Forces?
What is Gravity?
GRAVITY: An attraction force between
all masses
 Newton’s universal law of
gravitation: Every object in the
universe exerts a gravitational
attraction to all other objects in the
 The amount of gravitational force
depends upon the mass of the objects
and the distance between the objects
What is Gravity?
The greater the mass, the greater
the force
The greater the distance, the less
the force
Acceleration due to gravity = 9.8
m/s/s or 9.8 m/s2
Gravity in Space
Weight is a measure of the gravitational
force between two objects
The greater the mass the greater
the force (weight)
Measured in units called newtons (N)
Weightlessness – free from the effects
of gravity
Gravity by Brainpop
1) How does the gravity on the
moon compare to the gravity on
2) Why don’t you notice your own
gravitational pull on the Earth?
3) On what two things does the
force of gravity depend?
Air resistance:
The force of air exerted on a
falling object
The air pushes up as gravity pulls down
Dependent upon the shape and surface
area of the object
When the air resistance equals the force
of gravity, terminal velocity is reached
Terminal velocity is the highest velocity
that an object will reach as it falls
What is Motion?
Motion: A change in position of an object
compared to a reference point
Motion involves all of the following:
What is Motion?
The rate of change in position
Speed = distance ÷ time or
= distance
What is Motion?
Speed plus direction
Example: 50 km/hour north
What is Motion?
The rate of change in velocity
Positive acceleration = speeding up
Negative acceleration = slowing down (decelerate)
Acceleration = Vfinal – Vinitial
= ∆Velocity
What is Friction?
Friction = A force that opposes or slows
down motion
 Caused by the physical contact
between moving surfaces
 The amount of friction depends upon
the kinds of surfaces and the force
pressing the surfaces together
 Changes motion into heat
What is Friction?
What are some ways athletes uses
Acceleration by Brainpop
1) What units are used to measure
2) What units are used to measure
3) What is another way to say
“slowing down” in terms of
First Law: An object at rest stays at rest or
an object in motion, stays in motion (in
the same direction/at the same speed)
unless acted upon by an unbalanced
Also called the law of inertia
 A property of matter
 The tendency of an object to
resist any change in its motion
 The greater the mass the
greater the inertia
 The greater the speed the
greater the inertia
Examples of Newton’s 1st Law
a) car suddenly stops and you strain against the seat belt
b) when riding a horse, the horse suddenly stops and you
fly over its head
c) the magician pulls the tablecloth out from under a
table full of dishes
d) the difficulty of pushing a dead car
e) lawn bowling on a cut and rolled lawn verses an uncut
f) car turns left and you appear to slide to the right
Examples of Newton’s 1st Law
Second law: The greater
the force applied to
an object, the more
the object will
accelerate. It takes
more force to
accelerate an object
with a lot of mass
than to accelerate
something with very
little mass.
The player in black had more
acceleration thus he hit with a
greater amount of force
Second law:
The greater the force, the greater the
The greater the mass, the greater the
force needed for the same acceleration
Calculated by: F = ma
(F = force, m = mass, a = acceleration)
Examples of Newton’s 2nd Law
a) hitting a baseball, the harder the hit, the faster the ball
b) accelerating or decelerating a car
c) The positioning of football players - massive players on
the line with lighter (faster to accelerate) players in the
d) a loaded versus an unloaded truck
Examples of Newton’s 2nd Law
Examples of Newton’s 2nd Law
The second law states that
unbalanced forces cause
objects to accelerate with an
acceleration which is directly
proportional to the net force
and inversely proportional to
the mass. This one is telling
us that big heavy objects
don’t move as fast or as
easily as smaller lighter
objects. It takes more to
slow down a charging bull
then to slow down a
charging mouse.
third law: For every
action force,
there is an
equal and
reaction force.
(Forces are
always paired)
Examples of Newton’s 3 Law
a) rockets leaving earth
b) guns being fired
c) two cars hit head on
d) astronauts in space
e) pool or billiards
f) jumping out of a boat onto the dock
g) sprinklers rotating
Examples of Newton’s 3 Law
Newton’s third law: "For every action, there is
an equal and opposite reaction." When you fire
a gun you feel the recoil. Some of the funniest
things in cartoons follow physics that have
been exaggerated or just plain ignored. Wyle
Coyote hangs suspended in space over that
canyon for a lot longer than an object would
in reality, but it is the anticipation of the drop
and Wyle's facial recognition of the upcoming
pain that is so classically cartooney. So some
laws are stretched for comical effect.
Examples of Newton’s 3rd Law
Momentum: The quantity of motion
A property of moving objects
Calculated by: P = mv
(p = momentum, m = mass, v = velocity)
Law of conservation of momentum:
the total amount of momentum of a
group of objects does not change
unless outside forces act on the
Newton’s Laws by Brainpop
1) Why does a ball roll across a rug
and come to a stop?
2) What is a net force?
3) Give an example of Newton’s 3rd
Force by Brainpop
1) What famous physicist are units of
force named after?
2) What does velocity measure?
3) If Moby has a mass of 50 kg and
Tim has a mass of 40 kg, who would
require more force to move?