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59 terms

Chapter 5 - Work and Machines

Parker 8th grade
STUDY
PLAY
work
the product of force and distance when force is used to move an object
joule
unit of work, the SI unit of energy
machine
a device that changes the amount of force exerted or the direction in which force is exerted
input force
the force exerted on a machine
output force
the force applied by a machine
mechanical advantage
the number of times the force exerted on a machine is multiplied by the machine
efficiency
the percentage of the input work that is converted to output work
actual mechanical advantage
the mechanical advantage that a machine provides in a real situation
ideal mechanical advantage
the mechanical advantage that a machine would have without friction
inclined plane
a simple machine consisting of a flat surface with one end higher than the other
wedge
a simple machine consisting of a device that is thick at one end and tapers to a thin edge at the other
screw
a simple machine that consists of an inclined plane wrapped around a central cylinder to form a spiral
lever
a simple machine consisting of a rigid object that pivots about a fixed point
fulcrum
the fixed point around which a lever pivots
wheel and axle
a simple machine consisting of two circular objects that are fastened together and rotate about a common axis
pulley
a simple machine consisting of a grooved wheel around which is wrapped a rope, chain, or cable
compound machine
a device that combines two or more simple machines
gears
two or more wheels linked together by interlocking teeth
ideal machine
machine with no friction
W(in)=W(out)
Simple machines do not multiply energy
W(out) is never > W(in)
A watt is equal to __________
one newton per second
Work
A transfer of energy when a force makes an object move in the same direction (Joules)
Power
The rate or amount of work being done in one second (Watts)
mechanical advantage
how many times a machine multiplies a force
efficency
input compared to output
simple machine
machine that has only 1 movment
compound machine
combination of simple machines
The Force-Distance Trade-off
Machines often will increase the distance of the object has to move, but the input effort force is decreased. The same amount of work is done.
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
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.
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
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.