Science Explorer Chapter 4 Work And Machines

Front 1

What is the mathematical equation for WORK?

Back 1

Work = force x distance

(eg: newton x meters)

Hint 1

work = force times...what?

Front 2

What is the verbal definition of WORK?

Back 2

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.

Front 3

Is lifting a heavy box work?

Back 3

YES--the force applied and motion of the box were both UPWARD (same direction)

Front 4

is carrying a heavy box work?

Back 4

NO--the force applied was upward, but the motion was forward. Force and motion NOT same direction, so NOT work.

Front 5

what's a joule?

Back 5

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)

Front 6

what's a newton?

Back 6

a unit of force

Front 7

what is a machine?

Back 7

a device that makes work easier or more effective by changing the amount of FORCE you exert (note: it doesn't decrease the work!)

Front 8

what are the types of simple machines?

Back 8

inclined plane, gear, pulley, screw, wheel and axle, lever, wedge

Front 9

what's input force?

Back 9

the force you exert on the machine

Front 10

what's output force?

Back 10

the force exerted by the machine (also called resistance force)

Front 11

What are the three ways a machine can make work easier?

Back 11

multiplying distance
multiplying force
changing direction

Front 12

what's the verbal definintion of mechanical advantage?

Back 12

the number of times the output force of a machine is greater than the input force

Front 13

what's the mathematical equation of mechanical advantage?

Back 13

mechanical advantage =
output force/input force
("output force" divided by "input force")

Front 14

if your machine is multiplying force, it's mechanical advantage will be: more, less, or equal to 1?

Back 14

more

Front 15

if your machine is multiplying distance, it's mechanical advantage will be: more, less, or equal to 1?

Back 15

less

Front 16

if your machine is only changing direction, it's mechanical advantage will be: more, less, or equal to 1?

Back 16

equal

Front 17

what's the verbal definition of efficiency?

Back 17

output work compared to input work (usually expressed as a percentage, always less than 100%)

Front 18

How do you calculate efficiency?

Back 18

As a percentage: (output work/input work) x 100% = percent efficiency

{always less than 100%}

Front 19

Why is there no machine with 100% efficiency?

Back 19

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)

Front 20

What's the unit of measurement used to measure work?

Back 20

a Joule

Front 21

What's the unit of measurement used to measure work?

Back 21

a Newton

Front 22

What's "ideal mechanical advantage"?

Back 22

ideal mechanical advantage =
Output force/input force
(and you ignore the effect of friction. In real life, you'll never quite achieve this)

Front 23

What's "actual mechanical advantage"?

Back 23

actual mechanical advantage =
measured output force/measured input force
(you have to really measure it, so friction will be taken into account)

Front 24

Can a machine decrease the amount of work you need to do?

Back 24

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.

Front 25

Why is ideal mechanical advantage different from actual mechanical advantage?

Back 25

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.

Front 26

What do you need to know to calculate the efficiency of a machine?

Back 26

output work and input work (output work divided by input work, times 100%)

Front 27

Can a machine increase both force and distance? Explain.

Back 27

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.

Front 28

What's a manipulated variable?

Back 28

it's the factor the scientist changes in the experiment (like the number of pennies you placed first in the seesaw experiment)

Front 29

What's a responding variable?

Back 29

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)

Front 30

How do you calculate the ideal mechanical advantage of an inclined plane?

Back 30

ideal mechanical advantage =
length of incline/height of incline

Front 31

How are wedges and screws related?

Back 31

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.

Front 32

Which has a greater mechanical advantage: a screw with wide threads, or a screw with threads closer together?

Back 32

More threads = more mechanical advantage, so the screw with closer threads has more mechanical advantage

Front 33

What's a fulcrum?

Back 33

A fixed point that a lever pivots around (like the middle point of a see-saw)

Front 34

What's a first class lever? Give an example.

Back 34

Fulcrum in the middle, between output and input forces (like a seesaw, scissors, or pliers)

Front 35

What's a second class lever? Give an example.

Back 35

Fulcrum on one end, then the output force, then the input force on the other end (like a wheelbarrow, door, nutcracker, or bottle opener)

Front 36

What's a third class lever? Give an example.

Back 36

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)

Front 37

How do you calculate ideal mechanical advantage for a LEVER?

Back 37

ideal mechanical advantage =
distance from fulcrum to input force/distance from fulcrum to output force

Front 38

What point on a lever doesn't move?

Back 38

The fulcrum point.

Front 39

What kind of simple machine is a screwdriver, or a doorknob?

Back 39

wheel and axle

Front 40

How do you calculate ideal mechanical advantage for a WHEEL & AXLE?

Back 40

ideal mechanical advantage =
radius of wheel/radius of axle

Front 41

How do you calculate ideal mechanical advantage for a PULLEY SYSTEM?

Back 41

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)

Front 42

What's a compound machine?

Back 42

a machine that uses more than one simple machine (like a car: wheel & axle, gears, levers for the door handles, etc.)

Front 43

What kind of machine is your arm? Explain.

Back 43

A lever. One fulcrum is your elbow, the levers are your arm bones, and the muscles apply the input force.

Front 44

What kind of machine are your front teeth?

Back 44

Wedges.

Front 45

What's a tendon?

Back 45

Tough connective tissue that attaches your muscles to your bones.