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 kinetic energy.
- 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:^^
- They can increase the size of the input force, making your force stronger.
- They can increase the distance over which your force acts, making your force last longer.
- They can change the direction 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==, but it CAN NOT do both at the same time.
==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 less 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 Fulcrum in the middle.
- A 2nd class lever has the Load in the middle.
- A 3rd class lever has the Effort 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 mechanical advantage could be greater than, equal to, or less than 1. ^^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 mechanical advantage is always greater than 1. ^^So a 2nd class lever will always increase the amount of our input force.^^
With a 3rd class lever, the mechanical advantage is always less than 1. ^^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@@