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Transcript of Simple Machines
How it works...
How it works...
~a device that allows you to do work in a way that is easier~
INPUT AND OUTPUT
~Input and Output Forces
The lenses of a pair of glasses help you see things clearer if you have bad vision.
You may think machines have to be complex, but most machines are as simple as the examples below.
Scissors assist you while
A bicycle helps you transport to places you need to go to. It also saves energy and keeps you healthy. Riding bikes is good for the ecosystem because it doesn't put off exhaust like motorized vehicles do.
A lock keeps your valuable items safe such as your house or a lock on your safe (which contains money and other valuables).
~Input and Output Work
A machine makes work easier by changing at least one of the factors. A machine may change the amount of force you exert, the distance over which you exert your force, or the direction in which you exert your force.
Friction and Efficiency
Real and Ideal Machines
Ideal Mechanical Advantage=
Length of lncline
Height of Incline
How it works...
How it works...
Different Types of Levers
Ideal Mechanical Advantage=
Distance from fulcrum to input force
Distance from fulcrum to output force
WHEEL AND AXLE
How it works...
Radius of Wheel
Radius of Axle
How it works...
TYPES OF PULLEYS
Block and Tackle
SIMPLE MACHINES IN THE BODY
Work= Force x Distance
When a machine increases force, you must exert the input force over a greater distance.
small input force x large input distance = large input force x small output distance
When a machine increases distance, you must apply a greater input force.
large input force x small input distance = small output force x large output distance
When a machine changes the direction of the input force, the amount of force and the distance remain the same.
small input force x large input distance =
large output distance x small input force
input force: the force you exert on the machine
The input force moves the machine a certain distance, called the input distance.
output force: the force the machine exerts on an object
The machine does work by exerting a force over another disance,
called the output distance.
input work: the input force times the input distance
output work: the output force times the output distance
When you use a machine, the amount of output work can never be greater than the amount of input work.
~a machine's mechanical advantage is the number of times a machine increases a force exerted on it~
When the output force is greater than the input force, the mechanical advantage of a machine is greater than 1.
example: Suppose you exert an input force of 10 newtons on a hand-held bottle opener, and the opener exerts an output force of 40 newtons on a bottle. The mechanical advantage of the opener is 40 N (output force) divided by 10 N (input force). This equals 4. The bottle opener quadruples your input force.
For a machine that increases distance, the output force is less than the input force. (The mechanical advantage is less than 1)
example: Suppose your input force is 10 N and the machine's output force is 5 N. The mechanical advantage is 5 N (output force) divided by 10 N (input force). This equals 1/2. The output force of the machine is half your input force, but the machine exerts that force over a longer distance.
If the direction is the only variable that's changing, the input and output forces will be the same. The mechanical advantage will always be 1.
If you have ever tried to cut the stem of plant with a pair of shears that barely open and close, you know that a large part of your work is wasted overcoming the tightness, or friction, between the parts of the shears.
Forces from machines are lost when the machine is trying to overcome friction. The less friction there is, the closer the input work is to the output work. The efficiency of a machine compares the output work to the input work. Efficiency is expressed as a percent. The higher the percent, the more efficient the machine is. You can calculate a machine's efficiency if you know the input work and the output work for a machine.
To calculate the efficiency of a machine, divide the output work by the input work and multiply the result by 100 percent.
Ideal machines are machines with 100% efficiency. Machines like this, unfortunately, do not exist. All machines have an efficiency of less than 100%. In every machine, some work is wasted by the force of friction.
A machine's ideal mechanical advantage is its mechanical advantage with 100% efficiency. If you measure a machine's input force and output force, however, it will always be less than 100%. A machine's measured mechanical advantage is called actual mechanical advantage.
There are six basic kinds of simple machines: the inclined plane, the wedge, the screw, the lever, the wheel and axle, and the pulley. Simple machines are machines that help make work easier.
~a flat, sloped surface~
The reason you can exert your input forces over long distances is because of inclined planes. The input force needed, as a result, is less than the output force. The force with which you push or pull on an object is the input force that is used on an inclined plane. The force that you would use to lift the object without the inclined plane is the output force.Therefore, it is equal to the weight of the object.
You can determine the ideal mechanical advantage of an inclined plane by dividing the length of the incline by its height.
example: Suppose you are loading a truck that is 2 meters high using a ramp that is 6 meters long, the ideal mechanical advantage of the ramp is 6 meters divided by 2 meters, or 3. The inclined plane increases the force you exerted 3 times. If the height of the incline does not change, increasing the length of the incline will increase the mechanical advantage. The longer the incline, the less input force you need to push or pull an object.
~a device that is thick at one end and tapers a thin edge at the other end~
Using a wedge is like using an inclined plane. Instead, however, you don't move objects along the inclined plane. You move the inclined plane itself. Wedges are used in your everyday life. A zipper depends on wedges to close and open.
The mechanical advantage of the wedge and the inclined plane are similar. The ideal mechanical advantage of a wedge is determined by dividing the length of the wedge by its width. The greater its mechanical advantage, the longer and thinner the wedge is.
~can be thought of as an inclined
plane wrapped around a cylinder~
When you twist a screw into a wall, you exert an input force on the screw. The threads of a screw act like an inclined plane to increase the distance over which you exert the input force. As the threads of the screw turn, they exert an output force on the wall, pulling the screw into the wall.Friction between the screw and the wall holds the screw in place.
The closer together the threads of a screw are, the greater the mechanical advantage. This is because, the closer together the threads are, the more times you must turn the screw to fasten in into the wall. Your input force is applied over a longer distance. The longer input distance results in an increased output distance. The ideal mechanical advantage of a screw is the length around the threads divided by the length of the screw.
EXAMPLES OF SCREWS
~a rigid bar that is free to pivot, or rotate, on a fixed point~
The fixed point that a lever pivots around is called the fulcrum. To understand how levers work, think about using a bottle opener. The opener rests against the edge of the bottle, which acts as the fulcrum. The tip of the opener is under the bottle cap. When you push down, you exert a force on the handle, and the opener pivots on the fulcrum. As a result, the tip of the opener pushes up, thereby exerting an output force on the bottle cap.
A lever like a bottle cap opener helps in two ways. It increases your input force and changes the direction of your input force. When you use the bottle cap opener, you push the handle a long distance down to move the cap a short distance up. However, you are able to apply a smaller force than you would without the opener. The ideal mechanical advantage of a lever is determined by dividing the distance from the fulcrum to the input force by the distance from the fulcrum to the output force.
When a bottle opener is used as a lever, the fulcrum is located between the input and output forces. This is not always the case. There are three different types of levers. Levers are classified according to the location of the fulcrum relative to the input and output forces.
First-class levers always change the direction of the input force. If the fulcrum is closer to the output force, these levers also increase force. If the fulcrum is closer to the input force, these levers also increase distance.
These levers increase force, but do not change the direction of the input force.
These levers increase distance, but do not change the direction of an input force.
~two circular of cylindrical objects fastened together that rotate about a common axis~
When you use a screw driver, you apply an input force to turn the handle, or wheel. Because the wheel is larger than the shaft (axle), the axle rotates and exerts a large output force. The wheel and axle increases your force, but you must exert your force over a long distance.
You can find the ideal mechanical advantage of a wheel and axle by dividing the radius of the wheel by the radius of the axle. The greater the ratio between the radius of the wheel and the radius of the axle, the greater the mechanical advantage.
~a grooved wheel with a rope or cable wrapped around it~
The input force is when you pull on one
end of the rope. At the other end of the rope, the output force pulls up on the object you want to move. Using a pulley to move heavy objects makes work easier in two ways. It can decrease the amount of input work needed to lift the object. The pulley can change the direction of your input force. For example, you pull down on the flagpole rope and the flag moves up.
The ideal mechanical advantage of a pulley is equal to the number of sections of the rope that supports the object.
A pulley that you attach to a structure is called a fixed pulley. A fixed pulley does not change the amount of force applied. It does change the direction of the force.
If you attach a pulley to an object you wish to move, you use a movable pulley. A movable pulley decreases the amount of input force needed. It does not change the direction of the force.
By combining fixed and movable pulleys, you can make a pulley system called a block and tackle.
~machines are involved in much of the work that your body does~
Most of the machines in your body are levers that consist of bones and muscles. Every time you move, you use a muscle. Your muscles are connected to your bones by connecting structures called tendons. Tendons and muscles pull on bones, making them work as levers. The joint, near where the tendon is attached to the bone, acts as the fulcrum. The muscles produce the input force. The output is used for doing work, such as lifting your hand.
When you bite into a sour patch kid, You use your sharp front teeth called your incisors. Your incisors are shaped like wedges to enable you to bite off pieces of food. When you bite down on something, the wedge shape of your front teeth produces enough force to break it into pieces, just as an ax splits a log. The next time you take a bite out of a chewy sour patch kid, think about the machines in your mouth.
~a machine that utilizes two or more simple machines~
The ideal mechanical advantage of a compound machine is the product of the individual ideal mechanical advantages of the simple machines that make it up.
An apple peeler is a
compound machine. Four
different simple machines
make it up. The handle is
a wheel and axle. The
axle is also a screw that
turns the apple. A wedge
peels the apple's skin. To
hold the machine in place,
a lever can be switched to
engage a suction cup.
binder- helps students/ teachers stay organized and carry around papers and such
pencils- helps you write
stage ramp- helps transport rolling musical intruments and props to the stage
lotion top- keeps lotion contained
glue top- keeps glue from getting everywhere
bottom of chap stick- raises and lowers chap stick
jar- keeps food fresh
maxilla and mandible joint- moves your mouth to eat and talk
screw- holds pictures and such up on the wall
elbow joint- moves your arm up and down
pencil sharpener- helps keep your pencils sharp
zipper- keeps your jackets and such closed
counselor mailbox- helps keep the box closed
bottle cap- keeps your drink from spilling
music stand- keeps music upright while you are performing
scissors- help cut things
scissors- help cut things
baseball bat- helps hit baseballs
bottle opener- helps open
wheel barrow- helps move dirt from one place to another
handicapped ramp- A handicap ramp assist handicapped people while getting from the parking lot to the sidewalk.
hill- The hill helps you go to a higher surface
letter openers- help open letters
makeup sponges- help put makeup on
ax- helps cut wood
screw driver- helps put nails in the wall
tire- helps move vehicles
paddle wheel- helps move the boat
door knob- helps lock doors
steering wheels- helps direct tires on vehicles
door handle- helps open the door
tape dispenser- helps you tear tape faster and easier
bicycle chain- helps keep the wheels moving and change the gears
crane- helps move large objects
flag pole- keeps flags waving in the air and off of the ground