Transcript effort force

PASS Content Standard 2.1
Objects change their motion only when
a net force is applied. Laws of motion are
used to determine the effects of forces
on the motion of objects.
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Motion - 12 min
• Earth rotates
on its axis
at 1,100 mph
• Earth orbits
the Sun at
68,000 mph
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• The whole galaxy rotates
at 490,000 mph
Two Dimensional World
distance
Speed =
time
A snail crawls 10 feet in 5 minutes.
What is the speed of the snail?
distance
Speed =
time
10 feet
=
= 2 feet/min
5 minutes
total distance
Average speed =
total time
A boy runs 1 mile in 6 minutes, rests for
2 minutes, then walks 1 mile in 12
minutes. What is his average speed?
total distance
Average speed =
total time
1 mile + 1 mile
=
2 miles
=
20 minutes
20 minutes
Distance
(meters)
Time (seconds)
is a vector quantity
because it has both
speed and direction.
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Vectors - 12 min
All these planes have
the same speed.
How is
their
velocity
different?
The length of the line represents
the quantity (speed) and the arrow
indicates the direction.
Add vectors head to tail.
Direction is
indicated by
compass degrees
The magnitude
of the speed is
indicated by
the measured
length (scale)
of the line.
90
o
An airplane is flying 200
o
mph at 50 . Wind velocity
o
is 50 mph at 270 . What
is the velocity of the plane?
180
o
0
270
o
o
90
180
o
o
0
270
o
o
90
180
o
o
0
270
o
o
90
180
o
o
0
270
o
o
90
180
o
o
0
270
o
o
90
180
o
o
0
270
o
o
Velocity(final) - Velocity(original)
Acceleration
=
time
A car traveling at 60 mph
accelerates to 90 mph
in 3 seconds. What is the
car’s acceleration?
A car traveling at 60 mph accelerates to
90 mph in 3 seconds. What is the
car’s acceleration?
Acceleration
=
Velocity(final) - Velocity(original)
time
=
=
90 mph - 60 mph
3 seconds
30 mph
3 seconds
= 10 mph/second
A car traveling at 60 mph slams
on the breaks to avoid hitting
a deer. The car comes to a safe
stop 6 seconds after applying
the breaks. What is the
car’s acceleration?
A car traveling at 60 mph slams on the breaks to
avoid hitting a deer. The car comes to a safe stop
6 seconds after applying the breaks. What is the
car’s acceleration?
Acceleration =
Velocity(final) - Velocity(original)
time
=
=
0 mph - 60 mph
6 seconds
- 60 mph
6 seconds
= - 10 miles per hour per second
Acceleration toward the
center of a circular path.
For an object to travel in a
curved path, some force must
be accelerating it
toward the center
of the circle.
Force provided
by engine
Acceleration
provided
by tires
What happens if
the accelerating
force is removed?
The object
moves in a
straight line.
An apparent force
that appears only
in rotating frames
of reference.
This “false” force
appears to push
away from the
center of the
circular path.
If you are riding in the passenger
seat of this car, what do you feel?
What's actually happening?
Aristotle and Newton had different
ideas about forces and motion.
Aristotle's idea: For an
Newton's idea: An object
object to move at a constant
speed, a constant force
must be applied.
moving at a constant speed
will continue at that speed
without additional force
being applied.
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Produce
NO
Motion
Produce
Motion
Sliding - two solid surfaces rubbing
against each other.
Rolling - an object rolling over
a surface.
Fluid - an object moving
through a fluid.
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Newton’s Laws - 5 min
An object at rest
will remain at rest,
and a moving object
will remain at a
constant velocity
unless acted on
by unbalanced forces.
F = Ma
Force = mass X acceleration
For every action,
there is an equal
and opposite
reaction.
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Rockets - 6 min
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Momentum - 8 min
Does a long pendulum swing
faster than a short one?
Does a heavy pendulum swing
faster than a light one?
The total momentum of
any group of objects
remains the same
unless acted on by
outside forces.
Elastic - occur when both momentum
and kinetic energy are conserved.
Inelastic - occur when
momentum is conserved,
but kinetic energy is not.
M1V1 = M2V2
Before
After
Colliding objects have same mass
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Elastic Collision
Heavy object strikes light object
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Elastic Collision
Light object strikes heavy object
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Elastic Collision
Colliding objects have same mass
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Inelastic Collision
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Rollercoasters - 4 min
Units of Force are Newtons
Units of Distance are Meters
Newton
Meters = Joules
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Work - 2 min
A force of 200 Newtons is used
to move an object 10 meters.
How much work is done?
A force of 200 Newtons is used
to move an object 10 meters.
How much work is done?
W = Fd
A force of 200 Newtons is used
to move an object 10 meters.
How much work is done?
W = Fd
= (200 N)
A force of 200 Newtons is used
to move an object 10 meters.
How much work is done?
W = Fd
= (200 N)(10 meters)
A force of 200 Newtons is used
to move an object 10 meters.
How much work is done?
W = Fd
= (200 N)(10 meters)
= 2000 Joules
Power is the rate
at which work is done.
Units of Work are Joules
Joules per second = Watts
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power - 2 min
A machine produces 250 joules
of work in 2 seconds. How much
power is produced?
A machine produces 250 joules
of work in 2 seconds. How much
power is produced?
P=W/t
A machine produces 250 joules
of work in 2 seconds. How much
power is produced?
P=W/t
= (250 joules)
A machine produces 250 joules
of work in 2 seconds. How much
power is produced?
P=W/t
= (250 joules) / 2 sec
A machine produces 250 joules
of work in 2 seconds. How much
power is produced?
P=W/t
= (250 joules) / 2 sec
= 500 Watts
1 Horsepower
is equal to
745.56 Watts
or
550 ft lb/sec
The effort force is
applied to a machine.
The resistance force is
applied by a machine.
The number of times a machine
multiplies the effort force.
Work output
Work input X 100
Inclined Plane
An 800 pound motorcycle
is rolled up a 10 foot ramp
into a pickup bed that is
3 feet off the ground.
Calculate input work.
Calculate output work.
Calculate efficiency %.
Work input = 10 ft X 800 lb
= 8000 ft lb
Work output = 3 ft X 800 lb
= 2400 ft lb
% Efficiency =
Work output
2400 ft lb
Work input X 100
8000 ft lb X 100
0.3 X 100 = 30% Efficiency
Mechanical Advantage =
Length
10 ft
Height =
3 ft =
3.33 mechanical advantage
Machines make work
easier or faster . . .
but machines NEVER
produce more work
than is put into them.
In fact, because of friction,
more work goes
into a machine
than comes out.
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Climbing cars - 24 min
In 1868, a motion was passed
in congress to abolish the U.S.
Patent Office because all
important discoveries had
already been made.
Make work easier
because the effort force
moves over a greater
distance than the
resistance force.
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Inclined Plane - 2 min
Force is multiplied since
it is applied to a wide
area and exerted over
a small area.
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Wedge - 2 min
Multiplies an effort force
by acting through a
long effort distance.
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Screw - 1 min
A bar which moves
freely around a fixed
position, or fulcrum.
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Levers - 3 min
Three Parts of a Lever
Effort
Force
Resistance
Force
Fulcrum
The Fulcrum is between
the Effort Force and
the Resistance force
Multiplies Effort
Force and changes
its direction
The Resistance is
between the Effort
Force and the Fulcrum
Multiplies the Effort
Force but does not
change its direction
The Effort Force is
between the Resistance
Force and the Fulcrum
Does not multiply
the Effort Force and
does not change its
direction.
Does not multiply
the Effort Force and
does not change its
direction.
Direction of
the Effort Force
is changed.
Mechanical Advantage = 0
Direction of
the Effort Force
is not changed.
Mechanical Advantage = 1
Direction of the Effort
Force is changed.
Mechanical Advantage
is equal to the number
of supporting ropes.
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Pulleys - 1 min
A fixed pulley
does not have
a mechanical
advantage.
Fixed pulleys
only change
the direction
of the force.
A movable
pulley has a
mechanical
advantage.
The effort force
is in the direction
of the movement
of the resistance.
Two wheels of different sizes
connected - the axle being
the smaller wheel.
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Wheel & Axle - 1 min
Worm Gear
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Compound Machines - 4 min