Chapter #3 ~ Work and Simple Machines

==Work is done on an object when you apply a force to it and it moves in the direction of that force.==

• ^^When work is done on an object, its energy changes.^^
• If an object is pushed or pulled but ^^doesn’t move, no work is done on it.^^
• In the metric system, work is measured in %%joules (J)%%.

==When you do work on an object, you change its energy.  This is an important idea known as the Work-Energy Theorem. (The work is always EQUAL to the energy)==

• $By pushing or pulling an object, you give it <strong>kinetic energy.</strong>$
• By lifting an object, you give it potential energy.  You also give it kinetic energy while you’re lifting it.

==Power is the rate at which work is done.  As we said in class, it’s a measure of how quickly (or slowly) you do work on an object.==

• In the metric system, power is measured in %%watts (W).%%
• The $more work is done on an object, the more power$ will be used to do that work.
• The $more time it takes to do work, the less power$ will be used to do that work.

==A machine is any device that makes work easier.==

• Machines don’t decrease the amount of work done.  They make doing the work easier by changing how the work is done.
• $With any machine, there are always two forces involved:$  ==The input force (which you use on the machine), and the output force (which the machine uses on something else).==
• $With any machine, there are always two distances involved:$  ==The input distance (which you use on the machine), and the output distance (which the machine uses on something else).==

^^There are three (3) ways machines can make work easier to do:^^

1. $They can increase the size of the input force, making your force <strong>stronger.</strong>$
2. $They can increase the distance over which your force acts, making your force <strong>last longer</strong>.$
3. $They can change the <strong>direction</strong> in which a force is applied$.

==With any machine, there is always a tradeoff.  The tradeoff in a machine is that it can increase the strength of your input force OR increase the distance over which it acts==, $<strong><strong>but it CAN NOT do both at the same time</strong></strong>.$

==Mechanical advantage is a measure of how much a machine increases your input force.  It also tells us which of the three ways a machine is making work easier:==

• If the mechanical advantage is > 1, then the machine increases your input force, making it stronger.
• If the mechanical advantage is < 1, then the machine weakens your input force but makes it last a longer distance.
• $If the mechanical advantage = 1, then the machine changes the direction of your input force.$

==The efficiency of a machine is a percentage of how much useful work the machine can actually do.==  $It’s$ $always <strong>less</strong> than 100$

^^No machine can ever be 100% efficient, because friction is always present.^^

==Simple Machines do work by using only ONE MOVEMENT.==

==There are six (6) kinds of simple machines==:  ^^Levers, wheel & axle, screws, wedges, pulleys, and inclined planes.^^

With any simple machine, there is always a TRADEOFF- either a machine can increase the amount of our input force, or make our input force last a longer distance, but it ==CAN NOT DO BOTH.==

==A lever is a simple machine that pivots, or rotates, around a fixed point.==

• ==The pivot point of the lever is known as the fulcrum.==
• ==The input force you use to operate the lever is known as the effort.==
• ==The output force that the lever lifts/lowers is known as the load.==

==The mnemonic “Frogs Lay Eggs” can help you remember the three classes of levers:==

• $A 1st class lever has the <strong>F</strong>ulcrum in the middle.$
• $A 2nd class lever has the <strong>L</strong>oad in the middle.$
• $A 3rd class lever has the <strong>E</strong>ffort in the middle.$

@@A good example of a 1st class lever is a seesaw.@@

@@A good example of a 2nd class lever is a wheelbarrow.@@

@@A good example of a 3rd class lever is a broom@@.

$With a 1st class lever, the <strong>mechanical advantage</strong> could be <strong>greater than, equal to, or less than 1.</strong>$  ^^This means that a 1st class lever could increase our input force, change the direction of our input force, or make our^^ ^^input force last a longer distance.^^

$With a 2nd class lever, the <strong>mechanical advantage</strong> is <strong>always greater than 1.</strong>$  ^^So a 2nd class lever will always increase the amount of our input force.^^

$With a 3rd class lever, the <strong>mechanical advantage</strong> is <strong>always less than 1.</strong>$  ^^So a 3rd class lever will always increase the distance our input force acts, making it last longer.^^

==A wheel and axle is an axle attached to the center of a wheel.  Both rotate together.  Wheel/Axles always increase the amount of our input force.==

@@Ex: Door Knob@@

==An inclined plane is a flat, sloped surface that makes lifting loads easier.  It also increases our input force but makes us apply the force a longer distance (the tradeoff).==

@@Ex: Ramp@@

==A wedge helps us by cutting or separating two objects.  It’s a sloped surface that moves.==

@@Ex: Teeth@@

==A screw is an inclined plane that is wrapped around a cylinder.==

@@Ex: Threads on a light bulb@@

==A pulley is a grooved wheel with a rope/chain/cable wrapped around it.  It helps us lift loads and change the direction of force applied.==

Ex:

 \n ==A compound machine is two or more simple machines that are put together to help us do work.  Compound machines are less efficient than simple machines at doing work.==

@@Ex: Scissor@@