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Work and Machines- Chapter 5

STUDY
PLAY
Work
the transfer of energy that occurs when a force (push or pull) moves on an object
Energy
the ability to cause change or do work
Energy
is transferred from the object that is doing the work to the object on which the work is done (i.e. carrying a box upstairs)
Work
force x distance (fd)
Newtons
force is measured in
Meters
distance is measured in
Joules
work is measured in
Joules
also known as Newton meters
Power
the amount of work done in a certain amount of time; the rate at which work is done
Power
work / time
Watts
power is measured in
Power
energy / time
Machine
a device that makes work easier
Machines
increase the force applied to the object
Machines
can be powered by a force applied by a person
Machines
they can be simple or complex
Machines
make work easier by changing the direction of an applied force (i. e. pulling down on blind sring as blinds fold up)
Machines
can increase the force by applying a smaller force over a a large distance versus a larger force over a shorter distance
Effort force
the force applied to a machine
Resistance force
the force applied by the machine to overcome resistance is called
Input work
work done by you on the machine
Output work
work done by the machine
The Ideal Machine
Input work = Output work (not possible due to friction)
Mechanical advantage
the number of times a machine multiplies the effort force
effort distance
De
resistance distance
Dr
mechanical advantage
Fr / Fe or De / Dr =
2.5 N
If Fe = 100 N and Fr = 250 N, what is the MA?
less than one
When MA is ____ ____ ___, the machine increases the distance moved or the speed
equals one
When the MA is ______ ___, the machine changes the direction of the Fe.
greater than one
When the MA is _______ ____ ___, the machine increases the Fe.
efficiency
the measure of how much of the work put into a machine is changed into useful output work
High efficiency machines
produce less heat from friction
Efficiency
W out / W in x 100%
oil grease
You can make machines more efficient with ___ ______.
Simple machine
a machine that does work with only one movement
Levers
barsthat are free to pivot or turn about a fixed point called a fulcrum
resistance arm
the distance from the fulcrum to where the resistance force is applied
half
When you double the distance, you can ____ the force
effort arm
the distance from the fulcrum to where the effort force is applied
first class lever
used to multiply the force and change the direction of the applied force (screwdriver opening a paint can)
second class lever
the resistance froce is located between the effort force and the fulcrum; multiplies force (wheelbarrow)
IMA
the length of the arm / length of the resistance arm
IMA
Le / Lr
pulley
a grooved wheel with a rope, chain, or cable running along the groove
fixed pulley
a modified first class lever that can multiply force and/or change the direction of the applied force; attatched to something that does not move
moveable pulley
one end of the rope is fixed and the wheel is free to move; it multiplies force by increasing the distance you pull
block and tackle pulley
a system of pulleys made of fixed and moveable pulleys; can have large mechanical advantages
wheel and axle
a machine made up of two wheels of different sizes that rotate together (doorknoibs, pencil sharpener)
larger wheel
the effort force is usually exerted on the
resistance force
the smaller wheel is the
gears
two or more interlocking wheels that may change the direction of the force
inclined planes
sloping surfaces that reduce the amount of force required to do work by increasing the distance over which the force is applied
length of slope / height of slope
For inclined planes, the IMA =
less force
As a ramp/inclined plane is made longer and less steep, ____ _____ is required.
screws
inclined planes wrapped in a spiral around a cylindrical post (twisted inclined planes
Wedge
inclined plane with one or two sloping sides that change the direction of the effort force (knife, axe, edge of scissors
compound machine
two or more simple machines used together