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45 Cards in this Set

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What is the mathematical equation for WORK?
Work = force x distance

(eg: newton x meters)
work = force times...what?
What is the verbal definition of WORK?
you do WORK on an object when you exert a FORCE on the object that causes it to MOVE in the same direction as the force applied.
Is lifting a heavy box work?
YES--the force applied and motion of the box were both UPWARD (same direction)
is carrying a heavy box work?
NO--the force applied was upward, but the motion was forward. Force and motion NOT same direction, so NOT work.
what's a joule?
a unit of work measuring how much work you do when using 1 newton of force to move an object 1 meter (newton x meter)
what's a newton?
a unit of force
what is a machine?
a device that makes work easier or more effective by changing the amount of FORCE you exert (note: it doesn't decrease the work!)
what are the types of simple machines?
inclined plane, gear, pulley, screw, wheel and axle, lever, wedge
what's input force?
the force you exert on the machine
what's output force?
the force exerted by the machine (also called resistance force)
What are the three ways a machine can make work easier?
multiplying distance
multiplying force
changing direction
what's the verbal definintion of mechanical advantage?
the number of times the output force of a machine is greater than the input force
what's the mathematical equation of mechanical advantage?
mechanical advantage =
output force/input force
("output force" divided by "input force")
if your machine is multiplying force, it's mechanical advantage will be: more, less, or equal to 1?
if your machine is multiplying distance, it's mechanical advantage will be: more, less, or equal to 1?
if your machine is only changing direction, it's mechanical advantage will be: more, less, or equal to 1?
what's the verbal definition of efficiency?
output work compared to input work (usually expressed as a percentage, always less than 100%)
How do you calculate efficiency?
As a percentage: (output work/input work) x 100% = percent efficiency

{always less than 100%}
Why is there no machine with 100% efficiency?
because there's always some friction, and that wastes some of the input work (that's why "perpetual motion machines" don't work--they'll slow down eventually)
What's the unit of measurement used to measure work?
a Joule
What's the unit of measurement used to measure work?
a Newton
What's "ideal mechanical advantage"?
ideal mechanical advantage =
Output force/input force
(and you ignore the effect of friction. In real life, you'll never quite achieve this)
What's "actual mechanical advantage"?
actual mechanical advantage =
measured output force/measured input force
(you have to really measure it, so friction will be taken into account)
Can a machine decrease the amount of work you need to do?
NO--it can make the work easier, but in the end the amount of work will be as much or more than it was originally.
Why is ideal mechanical advantage different from actual mechanical advantage?
FRICTION: in ideal mechanical advantage, you ignore it...but when you really measure the output (for actual mechanical advantage), it's there, decreasing the machine's work output.
What do you need to know to calculate the efficiency of a machine?
output work and input work (output work divided by input work, times 100%)
Can a machine increase both force and distance? Explain.
NO: if the machine increases force, then distance decreases; if the machine increases distance, then force decreases. If one goes up, the other goes down.
What's a manipulated variable?
it's the factor the scientist changes in the experiment (like the number of pennies you placed first in the seesaw experiment)
What's a responding variable?
it's the factor in the experiment that changes in response to the manipulated variable (like the position of the second stack of pennies used to balance the other stack in the seesaw experiment)
How do you calculate the ideal mechanical advantage of an inclined plane?
ideal mechanical advantage =
length of incline/height of incline
How are wedges and screws related?
They're both types of inclined plane: the wedge is like two inclined planes stuck together; the screw is like an inclined plane wrapped around a cylinder.
Which has a greater mechanical advantage: a screw with wide threads, or a screw with threads closer together?
More threads = more mechanical advantage, so the screw with closer threads has more mechanical advantage
What's a fulcrum?
A fixed point that a lever pivots around (like the middle point of a see-saw)
What's a first class lever? Give an example.
Fulcrum in the middle, between output and input forces (like a seesaw, scissors, or pliers)
What's a second class lever? Give an example.
Fulcrum on one end, then the output force, then the input force on the other end (like a wheelbarrow, door, nutcracker, or bottle opener)
What's a third class lever? Give an example.
Fulcrum on one end, then the input force, then the output force on the other end (like a rake, fishing pole, shovel, or baseball bat)
How do you calculate ideal mechanical advantage for a LEVER?
ideal mechanical advantage =
distance from fulcrum to input force/distance from fulcrum to output force
What point on a lever doesn't move?
The fulcrum point.
What kind of simple machine is a screwdriver, or a doorknob?
wheel and axle
How do you calculate ideal mechanical advantage for a WHEEL & AXLE?
ideal mechanical advantage =
radius of wheel/radius of axle
How do you calculate ideal mechanical advantage for a PULLEY SYSTEM?
ideal mechanical advantage =
number of rope sections that support the object (don't count the section of the rope you're pulling on; it doesn't support the object)
What's a compound machine?
a machine that uses more than one simple machine (like a car: wheel & axle, gears, levers for the door handles, etc.)
What kind of machine is your arm? Explain.
A lever. One fulcrum is your elbow, the levers are your arm bones, and the muscles apply the input force.
What kind of machine are your front teeth?
What's a tendon?
Tough connective tissue that attaches your muscles to your bones.