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Simple machines make the things we use in everyday life function. Engineers use and combine simple machines to design complex devices to make our lives easier!
Simple machines are basic devices that help accomplish physical tasks with few or no moving parts.
The five most common simple machines:
- screw jack
- lever
- pulley
Simple machines make work easier, but they do not decrease the amount of work you have to do.
Simple machines are designed to change the magnitude/direction of the force (remember, work = force x distance), making the task easier to perform.
Remember that in closed systems the total amount of energy is conserved. A machine cannot increase the amount of energy you put into it.
A simple machine can change the amount of force you must apply to an object, and the distance over which you apply the force. In most cases, a simple machine is used to reduce the amount of force you must exert to do work.
The downside is that you must exert the force over a greater distance because the product of force and distance, i.e. work, does not change.
These simple machines provide the mechanical advantage of the design and then engineers combine multiple simple machines to create more advanced tools like cars, bicycles, medical devices, and 3D printers.
EarthPen. (2022). Simple machines (Standard YouTube licence)
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Levers use mechanical advantage to make lifting or applying pressure easier. All levers are made of a bar and a pivot, called a fulcrum.
Levers have three main parts:
- effort - the amount of force applied by the user, also referred to as the input
- fulcrum - where the lever pivots
- load - the weight that needs to be moved, also referred to as the output
Mechanical advantage is the amount of help you get using a machine in comparison to doing something with just human effort, and it is created by levers.
It is measured by dividing the load by the effort applied to moving it, both measured in Newtons (N) - this could also be described as the output (load) divided by the input (effort).
Example
A person lifting a load of 200 N but only using 100 N of effort:
Therefore, the mechanical advantage = 200 ÷ 100 = 2.
This can also be written as 2:1. The person is able to lift twice the load using 100 N of effort.
The mechanical advantage can also be calculated theoretically by measuring the distance between the load and pivot and the effort and pivot.
In the picture below the distance between the load and fulcrum is 2 m. The distance between the effort and fulcrum is 6 m.
Therefore, the mechanical advantage = 6 ÷ 2 = 3 or 3:1
The person will find this load three times easier to lift.
In both examples the mechanical advantage could be calculated. It is possible to calculate any part of the formula as long as there are two pieces of information from the formula available.
TED-Ed. Peterson, A & Patterson, Z. (2014). The mighty mathematics of the lever. (Standard YouTube licence)
Classes of lever
There are three different types of levers. They are chosen for their ability to produce the most mechanical advantage for a particular task. These classes of lever arrange the effort, fulcrum, and load in a different order:
First order
Effort
Fulcrum
Load
Second order
Effort
Load
Fulcrum
Third order
Fulcrum
Effort
Load
First order levers (Class 1) place the fulcrum between the effort and the load. An example would be a seesaw, which places the fulcrum in the centre and allows equally weighted children to lift each other up.
If the load is closer to the fulcrum, it becomes easier to lift. When the fulcrum is in the centre, like a seesaw, the effort and the load must be equal to balance them. If a person is slightly heavier at one end or leans back, moving the weight, one end of the seesaw moves down.
When a lever is balanced it has equilibrium - the load is balanced on either side.
A crowbar is an example of a first order lever that puts the load closer to the fulcrum - this gives it more power to move a load. When the fulcrum is moved nearer the load it takes less effort to move it.
Scissors are a first order lever. The hand’s grip is the applied force, the fulcrum is the pin at the centre of the scissors and the blade applies force to the load.
The class 1 lever is probably the most familiar to most people. We often use it when we want to lift something we can't lift with just our muscles. The fulcrum is between the load and the applied force.
One of many class-1 levers in humans is the system that rotates the skull up and down. The fulcrum is the point where the skull connects to the spine. The applied force is the muscles on the back of the neck and the load is the weight of the front of the skull. Normal muscle tension in the bundle of muscles at the back of the neck holds the head level.
Second order levers (Class 2) place the fulcrum at one end of the lever and the effort at the other, with the load in the centre. The closer together the fulcrum and load are, the easier it is to lift the load. Examples include wheelbarrows, nutcrackers and some bottle openers.
In a class-2 lever system, the load is between the fulcrum and the applied force, as shown below.
The mechanical advantage in this system is the same as a class-1 lever. One common example is a door. The fulcrum is at one edge, the load is the weight of the door, which we can concentrate at its center of mass, and the applied force is at the edge opposite the hinges.
The muscles that stand you on tip-toe are the calves. They attach to the bottom of the femur and to the heel bone. The load of the weight of a human is transferred through the tibia, which is between the fulcrum (the ball of the foot) and the applied force (the constricting calves).
Third order levers (Class 3) place the effort between the fulcrum and the load. If the effort and the fulcrum are further apart, it becomes easier to lift. A third order lever does not have the mechanical advantage of first order levers, or second order levers so are less common. They are generally used for moving small or delicate items. Examples include tweezers or fishing rods.
Tweezers or cooking tongs have the fulcrum at the closed end, the load at the open end, and the force in between.
In a class-3 lever, the applied force is between the fulcrum and the load. In this configuration, the bar must be attached to the fulcrum, or else it would lift off.
In a 3rd-class lever, the maximum mechanical advantage is 1. Any position of the applied force other than directly opposite the load, results in an amplification of the force needed to move the load.
In order to raise a load held in your hand, your biceps, which attach to the strong bone of the forearm between the fulcrum (the elbow) and the hand, shorten and pull on the forearm bone (ulna), raising the load.
MooMooMath. (2020). Difference between 1st, 2nd and 3rd class levers. (Standard YouTube licence)
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Pulleys use mechanical advantage, similar to levers, to lift up loads. Pulleys are wheel shaped with a groove that allows a cord to sit inside the groove. They can be used by hand or attached to a motorised winch to increase the amount of weight that can be lifted.
Pulleys can either be fixed (stationary) or moving. The mechanical advantage in a pulley system is equal to the number of ropes leading to or coming from moving pulleys. In the simplest case, a single pulley is used to re-direct the force needed to move a load:
A single pulley changes the direction of force, making pulling down easier than lifting up. Single pulley systems are demonstrated in cranes, lifting a bucket from a well, raising a flag or adjusting window blinds. Even though there is no actual mechanical advantage with one pulley, it is referred to as having a mechanical advantage of one.
One pulley doesn’t make a mechanical advantage, as the same amount of force is needed. However, if additional pulleys are added, a mechanical advantage is created. Using two pulleys together means you need half the force to lift. This is called a block and tackle, and is used to lift large, difficult-shaped objects, such as furniture. Adding more wheels to the block and tackle increases the load it can lift.
In a 2:1 pulley system, shown below, a second pulley is attached to the load, and so moves along with it. In this system, there are two ropes attached to the moving pulley, giving a mechanical advantage of 2. So, the force required to lift the crate will be half of the weight of the load, but for every meter of lift, we'll have to pull 2 m of rope through the system.
The mechanical advantage is equal to the number of sections of rope pulling up on the object.
A 4:1 pulley system is shown below. It contains two moving pulleys, each with two ropes going to or coming from them. The four ropes attached to moving pulleys gives this system a 4:1 mechanical advantage.
The force needed to lift the load is ¼ of the load, but four times as much rope will have to be pulled through the system for each unit of lift of the load.
The mechanical advantage of a movable pulley (one where the pulley can move freely along the rope) is two.
Activity
1. Click on the link below:
https://www.compassproject.net/html5sims/pulleysim/pulley_en.html
2. On the right-hand side, change the pulley system to a single system, and pull down on the rope using 10 newtons of effort. Make a note of how many newtons were used to lift the load and the distance it rose.
3. Reset the simulation and change the pulley system to a double fixed.
Again, pull on the rope with 10 newtons of effort. Make a note of the distance the load rose. Compare it to the distance the load rose using a single pulley. What do you notice?
The 10 N load below would still require 10 N of force to lift as the extra pulley is not taking any additional strain in weight - the weight is still taken by only one section of rope.
4. Reset the simulation. Change the pulley to a single compound. Pull down on the rope until the effort arrow goes green. Note the amount of effort in newtons and the height the load was lifted.
Compare this to the two previous attempts. What do you notice?
The 10 N load below would require half of the force to lift. There are two sections of rope taking the strain, so 5 N of force would be needed to lift it. The mechanical advantage would be 2.
5. Reset the simulation and change the pully system to a double compound. Again, pull on the rope until the arrow goes green. Note the effort in newtons.
6. Reset the simulation and change the pully system to a triple compound. Again, pull on the rope until the arrow goes green. Note the effort in newtons.
You should notice that every time you add a pulley, the amount of effort required is reduced by half.
SmarterEveryDay. (2019). How pulleys work. (Standard YouTube licence) -
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An inclined plane is a sloping plane used to raise heavy bodies. Inclined planes make it easier to lift objects to greater heights. There are two ways to raise an object: it can be either raised by lifting it straight up or by pushing it diagonally up.
Lifting an object straight up moves the object in the shortest distance, but a more significant force must be exerted. Using an inclined plane to lift objects requires a smaller force but must be exerted over a long distance. A few everyday examples of inclined planes include sidewalk ramps, highway access ramps, inclined conveyor belts, and switchback roads.
In the diagram, the crate can be lifted directly to height, or it can be moved there via the inclined plane.
The effort required to lift the crate is more than the effort required to slide the box up the inclined plane, but the distance the box travels will be greater.
How Does an Inclined Plane Work
An inclined plane takes advantage of the slope or inclination, making it easier to work against gravity. The force required to overcome gravity is much less than required to lift an object vertically; the latter is equal to the object’s weight. However, the distance traversed by the object will be longer.
The mechanical advantage of an inclined plane is defined as the ratio of the output force to the applied force. It is expressed in terms of distances. The following equation gives the formula for ideal mechanical advantage.
ideal mechanical advantage = \[L/h\]
Where,
L: Length of the inclined plane
h: Maximum height of the inclined plane
According to the equation, the longer the plane, the easier moving an object upward. So, an inclined plane reduces the effort force by increasing the distance through which the force is applied.
The equation ignores the friction between the object and the inclined plane. The efficiency of an inclined plane is the ratio of the actual mechanical advantage and ideal mechanical advantage.
In reality, the actual mechanical advantage is always less than the ideal mechanical advantage. Hence, the efficiency is always less than 100%.
There are many examples of inclined planes that are used in real everyday life:
- A staircase is considered an inclined plane because it makes an angle to the surface. So, when a person climbs stairs, they are not climbing vertically.
- An escalator is an inclined plane since it is in the same category as a staircase.
- A ladder is considered an inclined plane because it is placed at an angle to the surface. When a person climbs the ladder, they are not climbing vertically.
Inclined planes serve many purposes ranging from basic needs to engineering applications.
- A sloping road connects a roadway to a bridge or overpass.
- A ramp is used instead of a staircase for wheelchairs and shopping trollies in departmental stores.
- Ancient pyramids had ramps that allowed laborers to roll up stones.
- A multistorey car park has ramps allowing vehicles to move from one level to another.
- A sloped driveway is used in front of houses for driving vehicles up to the entrance.
- Children use slides in a playground for fun.
- Houses have slanted roofs so that water and snow run off them.
Click on the link below to watch a YouTube video on inclined planes:How Inclined Planes MAKE WORK EASY!
Turtlediary. (2017). How inclined planes make work easy (Standard YouTube licence)
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An inclined plane wrapped around a shaft is known as a screw. The two primary functions of a screw are to hold things together or to lift objects. The threading around the shaft in a screw makes it an efficient tool to hold things together. The threads grip the surrounding material like teeth, resulting in a secure hold.
A screw is just a specialized version of the inclined plane. A bolt is a screw that is meant to slide into a pre-grooved receptacle with matching threads, such as a nut or a tapped (threaded) hole.
A few examples of screws include screw, bolt, clamp, spinning stool, and spiral staircase. A car jack is an example of a screw used to lift something.
A car jack is a mechanical device used to easily lift heavy loads cars, to gain an easy access to sections underneath vehicles or to simply just change a wheel. The most important fact of a jack is that it gives the user a mechanical advantage by changing rotational force into linear, allowing the user to lift heavy structures up that would be impossible to do without this tool.
JAES Company. (2020). What is jackscrew and how it works (Standard YouTube licence)
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The wheel is one of the most significant inventions in the history of the world. Before the invention of wheels, the amount of load and the distance through which we could carry the load over land was limited.
Wheeled carts facilitated agriculture and commerce by enabling the transportation of goods to and from markets, as well as easing the burdens of people traveling great distances.
Wheel and axle make work easier by moving objects across distances. The wheel and axle greatly reduce the friction involved in moving an object. The wheel (round ends) turns with the axle (or cylindrical post), causing movement.
In addition to reducing friction, a wheel and axle can also serve as a force multiplier. If a wheel is attached to an axle, and a force is used to turn the wheel, the rotational force, or torque, on the axle is much greater than the force applied to the rim of the wheel.
The wheel and axle is a type of simple machine used to make tasks easier in terms of manipulating force by applying mechanical advantage. The system changes the force by changing the distance over which the force must be applied, if the input force is reduced to \[1/5\] the output force, then the force must be applied over five times the distance.
The wheel and axle both rotate at the same rate. What this means is that both the axle and the wheel will complete one full rotation in the same amount of time. Due to the size difference in the radius of the wheel and axle, this means that the distance the two parts rotate through in the same amount of time is different. This is due to the difference in the circumferences of the wheel itself and the axle that supports it. This supplies the conditions for mechanical advantage.
The mechanical advantage for this system is ideally:
IMA=Rr
where R is the radius of the wheel, and r is the radius of the axle, shown in the diagram below:
A wheel and axle system need a force in order to lift the load, but that force can be less than the weight of the object. Although the force a person needs to apply may not be very large compared to the force it does on the object, the distance they need to rotate the wheel is much larger than the distance the axle rotates through.
MakerClub. (2018). How does a wheel and axle work? (Standard YouTube licence)
Examples of wheel and axle machines
1. Bicycle
A bicycle consists of an arrangement of wheel and axle that helps it move forward. Here, the force applied to the axle initiates the motion and causes the wheels of the cycle to move.
2. Car Tyres
The tyres of a car move forward or turn to either side with the help of an axle. When the engine of the car exerts a force on the axle, the wheels tend to move or rotate accordingly.
3. A Ferris Wheel consists of a giant wheel that rotates in a circular direction. The centre point of the Ferris wheel consists of a cylindrical rod known as the axle. The axle is subjected to a high magnitude electrical force, which supports the rotation of the Ferris wheel.
4. A doorknob closely resembles the wheel and axle simple machine. Here, the doorknob acts as the wheel, and the shaft present at the centre of the knob functions as the axle. When the knob is turned, a force is built on the shaft or the axle. This force helps retract the latch and open or close the door with ease.
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A machine that uses liquid to transmit a force is called a hydraulic system. The pressure in the liquid is the same everywhere in the system. The simplest type of hydraulic machine is made of two pistons connected by a liquid-filled pipe. If one piston is pushed, the force is transmitted through the liquid and the other piston moves. Hydraulic brakes on cars work like this.
Liquids are used in hydraulic systems because they are more difficult to compress than gases, so are better at transmitting forces - when a force is applied at one end of the system, it is easy transferred through the system.
Pascal’s principle (also known as Pascal’s law) states that when a change in pressure is applied to an enclosed fluid, it is transmitted to all portions of the fluid and to the walls of its container. In an enclosed fluid, since atoms of the fluid are free to move about, they transmit pressure to all parts of the fluid and to the walls of the container.
A simple hydraulic jack, like a car jack, is a good example of how Pascal's law is put into practice. Using such jacks, one can even lift buildings.
The hydraulic jack consists of a lever that pushes a piston into a narrow tube of some fluid, usually an oil. The lever allows a human to apply a lot of force to the fluid reservoir. The size of the fluid tube is expanded below a moveable piston that can be pushed upward to raise a mass. A reservoir of low-pressure oil and a couple of valves complete the jack so that it can be extended its full length, and sometimes further if the piston can telescope.
When the lever is pushed downward, the one-way filling valve closes, and the lower valve (which allows flow only in the right → left direction (in this figure). Because the diameter of the pumping piston is smaller than the diameter of the lifting piston, the force is multiplied, and the rising jack can lift large masses.
To full the pump, the handle is raised. The high-pressure (lower) valve shuts off, maintaining the fluid pressure under the lifting piston. The filling valve opens, as it allows fluid movement from right to left (in the figure) only. Fluid from the low-pressure reservoir enters the pump and is ready to be pushed into the high-pressure side.
Fuseschool. (2020). Hydraulics. (Standard YouTube licence)
A hydraulic press is a machine that uses Pascal’s Principle to generate a large amount of force. It consists of two cylinders, a smaller slave cylinder and a larger master cylinder. The slave cylinder contains a piston that is used to apply pressure to the fluid inside the slave cylinder. This pressure is then transferred to the master cylinder, where it is pushed by a piston.
Hydraulic presses are commonly used for forging, clinching, moulding, blanking, punching, deep drawing, and metal forming operations. Hydraulic presses are also used for stretch forming, rubber pad forming, and powder compacting. The hydraulic press is advantageous in manufacturing, it gives the ability to create more intricate shapes and can be economical with materials. A hydraulic press takes up less space compared to a mechanical press of the same capability.
Calculating the force on a piston:
A hydraulic car jack is used to lift a vehicle. The area of piston A holding the car is 40 m2 and the area of piston B, which the mechanic presses, is 0.5 m2. The mechanic exerts a force of 100 N on her piston. What is the force exerted on the car by piston B? (Remember that the pressure is the same in the entire system.)
First calculate the pressure on the surface of piston A:
On piston A, a force of 100 N is exerted over an area of 0.5 m2.
This is the pressure of the system.
Pressure = Force normal to the surface/area of the surface
Pressure = 100/0.5
Pressure = 200 Pa
Then calculate the force at piston B. First rearrange the equation to find force normal to surface area:
Force normal to a surface area = pressure × area of that surface
Force on piston B = 200 × 40
Force on piston B = 8,000 N
Activity
What you will need:
16 strong pieces of cardboard with a length 12cm and breadth of 1.5 cm, or 16 ice lolly sticks
20cm long pipe
18 strong bamboo sticks.
Two syringes, 1 of 10mls and the other 20ml. You can also use same size syringe.
Hot glue gun
Sharp knife
What you will do:
1. Make 3 holes in each piece of card board.
2. Cut eighteen bamboos sticks into 10 cm lengths.
3. Arrange all cardboard in crisscross and push through the bamboo sticks.
5. Seal the sticks into place with hot glue.
6. Repeat this process for the other side.
7. Glue a cardboard platform to the top of the chain.
8. Glue one of the syringes, the pressing end to the chain.
9. Fill the second syringe with water, and using the pipe connect another syringe.
10. Place an object onto the platform and using the syringe, lift the object up.
DIY Projects. (2018). Hydraulic jack (Standard YouTube licence)
Examples of hydraulic presses:
1. Hydraulic Lifts - used for moving goods or people vertically. Scissor lifts, two-post lifts, four-post lifts, carousel lifts, and mezzanine lifts are different types of hydraulic lifts used.
2. Hydraulic Brakes - Braking systems on vehicles are an important example of hydraulics.
3. Bicycle pump
4. Syringes
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