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science > ch 12 > Flashcards

ch 12 Flashcards

(49 cards)

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1
Q

What is work input?

A

the work put into a machine

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2
Q

What is a compound machine?

A

A combination of two or more simple machines

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3
Q

What is a machine?

A

A device that makes work easier

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4
Q

What are ways that machines make work easier?

A

-changing the required force that needs to be applied
-changing the required distance over which the force must be applied
-changing the direction in which the force must be applied

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5
Q

What is the formula for work?

A

force x distance

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6
Q

What is the formula for power?

A

work divided by time

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7
Q

What is power?

A

the rate at which work is done

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8
Q

What is work defined as?

A

a force acting through a distance

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9
Q

What is the formula for Joule’s?

A

Newton x meter

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10
Q

When is positive work done on an object?

A

when the object moves in the same direction in which the force is exerted.

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11
Q

If an object does not move…

A

no work is done

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12
Q

Work is only done..

A

when the force is acting through the distance

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13
Q

Any remaining distance the object travels after the force…

A

is no longer being applied to the object is not included in the calculation of work.

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14
Q

What is a joule?

A

an amount of work or energy that is equivalent to applying a 1 Newton force to an object for a distance of 1 meter

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15
Q

What is energy?

A

the ability to do work or cause change

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16
Q

What is the work required to raise an object some distance

A

by multiplying the object’s mass times the acceleration due to gravity to get an idea of the minimum force required to lift the object and then multiplying by the distance the object is raised.

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17
Q

If you wanna multiply a mass into a weight..

A

don’t forget to multiply by 9.8!

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18
Q

What is the formula for power when it is combined with work?

A

Power = (Force x Distance)/Time

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19
Q

joule/second =

A

Watt

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20
Q

What is a watt?

Study These Flashcards
A

the equivalent of applying a 1 Newton of force through a distance of 1 meter in 1 second

21
Q

How many Watts is 1 kilowatt equal too?

22
Q

How many Watts is one horse power equal to?

23
Q

Do machines change the amount of work done?

24
Q

Do machines make work easier?

Study These Flashcards
A

yes, by changing the way in which the work is done in at least one of three ways

25
What is the formula for work input?
Work input (WI) equals the input or effort force (FI) times the input distance (dI). WI = FIdI
26
What is work output?
The work that a machine does
27
What is the formula for work output?
Work output (WO) equals the output or resistance force (FO) times the output distance (dO). WO = FOdO
28
The work put into a machine...
is equal to the output work (WI = WO)
29
Machines can make it easier to do work by letting you use less force, but..
they require you to move something a longer distance. (ex. using a ramp to lift a cart means you don't have to push as hard but you have to push the cart further up the ramp)
30
When machines work in the opposite way...
They make you use more force but let you move something a shorter distance. (ex. when you ride a bike in high gear, you have to pedal harder, but you don't have to spin the pedals as much to go far)
31
If the required forces are changed when using a machine...
the required distances are also changed and vice versa
32
Is there an advantage when machines change the direction of the force?
yes (ex. instead of lifting smth heavy straight up, u can use a pulley.)
33
Some machines make work easier by changing the direction of the force you use, but they can also change how much force you need and how far you have to move something.
For example, a “block and tackle” system, which uses multiple pulleys, lets you pull down instead of lifting up. It also lets you use less force, but you have to pull the rope a longer distance to move the object.
34
Even though the total amount of work stays the same in theory, some of the work gets “lost” because of friction.
Friction creates heat, which means some of the energy gets turned into thermal energy instead of being used to do the work you want.
35
What is efficiency?
A comparison of input work to output work
36
Efficiency =...
WO/WI (work output/work input)
37
Can a machine be 100 % efficient?
no, due to friction and inefficiencies
38
Which machines tend to be the most efficient?
Machines with the smallest amount of friction
39
Mechanical advantage tells how many times the input force is multiplied.
The greater the mechanical advantage, the less force is required to do the work.
40
Mechanical Advantage = ...
Output Force / Input Force (MA = FO/FI)
41
Mechanical advantage is how much a machine helps you do work by making it easier. It’s a number that shows how much the machine multiplies your force.
For example, if a machine has a mechanical advantage of 3, it means you only need to use one-third of the force to do the same job. However, you might have to move something farther to make up for it.
42
What is the formula for Efficiency?
AMA / TMA (actual mechanical advantage divided my theoretical mechanical advantage)
43
An ideal machine is a machine that works perfectly, with no energy lost to things like friction. It would be 100% efficient, meaning all the energy you put in would be used to do the work.
But in real life, no machine is perfect. These are called real machines because they lose some energy to things like heat or friction.
44
All machines are either _____ or _____ simple machine.
one or more simple machine.
45
How many simple machines are there and what are they?
There are 6 and they are: Inclined plane, wedge, screw, lever, pulley, and wheel and axle
46
What is an inclined plane?
a flat, sloped surface like a ramp. - The longer the inclined plane is, the less force is needed to raise the object because of the decreased slope. Therefore, longer inclined planes with less slope yield greater mechanical advantages.
47
What is a wedge?
essentially a moving inclined plane. - Many wedges are made from two inclined planes stuck together like an ax. The longer and thinner the wedge, the greater its mechanical advantage. Its ideal (theoretical) mechanical advantage is calculated similar to an inclined plane’s ideal mechanical advantage. TMA = (Length of the wedge) / (Width of the wedge).
48
What is a screw?
an inclined plane wrapped around a central bar or cylinder to form a spiral. - A screw gets its mechanical advantage from the length of the inclined plane wrapped around it. The closer together the threads on a screw, the greater its mechanical advantage. TMA = (Length of the threads around the screw) / (Length of the screw).
49
What is a lever?
a rigid bar that is free to pivot about a fixed point called a fulcrum - A good example is the see-saw. There are three classes of levers. A first class lever has a fulcrum in the middle. A second class lever has the resistance in the middle.A third class lever has the effort in the middle. Just remember FRE. The numeric order of the letters in the word “FRE” corresponds with the class of lever that includes the fulcrum, resistance, or effort in the middle. Notice that different classes of levers change the direction of the input force. This can sometimes make work easier. The mechanical advantage of a lever is generated by changing the effort arm length relative to the resistant arm length. The effort arm length is the distance from the fulcrum to input force. The resistance arm length is the distance from the fulcrum to the output force. TMA = (Effort arm length) / (Resistance arm length).

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