Chapter 7 Machines… Making work easier

machines
a device that makes work easier
simple machines
a device that does work with only one movement
How do machines make work easier?
by changing the force your exert in size, direction, or both
How many forces are involved when a machine is used to do work?
2
What are the two forces called?
effort force and the resistance force
effort force
the force applied to the machine
resistance force
the force applied by the machine to overcome resistance
What is the symbol for effort force?
F
e
What is the symbol for resistance force
F
r
How much work can you get out of a machine?
Energy is always conserved. Therefore, you can never get more work out of the machine then you put into it.
ideal machine
a machine in which work input equals work output.
What are examples of ideal machines?
ideal machines do not exist
mechanical advantage
the number of times a machine multiplies the effort force
What is the symbol for mechanical advantage?
MA
How many simple machines are there?
6
What are the six simple machines?
levers, pulleys, wheel and axle, inclined planes, screws, and the wedge
lever
a bar that is free to pivot, or turn, about a fixed point.
What are examples of levers?
seesaw, can opener, tennis racket
fulcrum
the fixed point of a lever
effort arm
the part of the lever on which the effort force is applied
resistance arm
the part of the lever that exerts the resistance force
What is the symbol for Ideal Mechanical Advantage?
IMA
What is the formula to find the ideal mechanical advantage of a machine?
IMA=length of effort arm
______________________
length of resistance arm
How many classes of levers are there?
3
What are the classes of the levers based on?
the positions of the effort force, resistance force, and the fulcrum
first class
fulcrum located between the effort and resistance forces. Usually used to multiply force, can also be used to multiply distance
second class
resistance located between the effort force and the fulcrum. Always multiplies force
third class
effort force located between the resistance force and the fulcrum. Can’t multiply force. MA always less than one. It increases speed.
Pulleys
a pulley is a grooved wheel with a rope or a chain running along the groove.
How many types of pulleys are there and what are they called?
2. They are called fixed and movable pulleys
block and tackle
fixed and movable pulleys combined to make a system of pulleys
wheel and axle
a simple machine consisting of two wheels of different sizes that rotate together
What are examples of wheel and axles?
doorknobs, faucets, ice-cream maker
gears
modified wheel and axle machines
inclined plane
a sloping or slanted surface used to raise objects. A ramp is an example of an inclined plane
screw
an inclined plane wrapped in a spiral around a cylindrical post
wedge
an inclined plane with one or two sloping sides
What are examples of wedges?
chisels, knives, ax blades
What are the 6 types of simple machins variations of?
the lever and inclined plane
power
the measure of the amount of work done in a specific amount of time
What is power measured in?
watts, It equals 1 joule/second
compound machine
a combination of two or more simple machines
bionics
the science of designing artificial replacements for parts of the human body that are not working properly
What are artificial replacements for the human body called?
prostheses
efficiency
the ratio of the useful work put out by a machine to the work put into that machine; efficiency is always less than 100 percent
What does W stand for?
work
What does F stand for?
force
What does d stand for?
distance
What does W in stand for
work input
What does d e stand for
effort distance
What does W out stand for
work output
What does d r stand for?
resistance distance
What is the formula for work
W=F x d
What is the formula for work input
W = F x d
in e e
What is the formula for work output?
W = F x d
out r r
What is the formula for work input and work output in an ideal machine?
W W
in = out
How does a hammer used to pull a nail from a board change the direction of the force?
When you push down on the hammer, the claw pulls it up. It changes the direction of the force.
When you use a hammer to drive a nail into a piece of wood, are you changing the size or the direction of the force?
you are changing the size.
What simple machines are levers?
lever, wheel and axle, gear, and the pulley
What simple machines are inclined planes?
wedges, screws, and inclined plane
In a brain-to-computer interface, electrodes are used to collect —— from the brain
signals