Machines are tools that help humans do work
Machines help people use energy more effectively.
A device that helps us to do work.
An example of technology developing is a combine harvester.
Simple Machines – Meet Human Needs
1) Were very simple devices
2) Depended on people & animals for their source of energy.
3) Example: Plow
How did earlier civilizations get water to their homes?
(I) Roman Aqueducts
Used for transporting water for many kilometres to supply cities.
Had 3 parts: Pump – raise water into reservoirs.
Channels – on a slope to carry the water.
Distribution system – distributes water within a city.
(II) Sakia (Persian wheel)
- Series of buckets attached to a long rope, draped over a wheel.
- Wheel is turned by animals which raises the buckets of water.
- After water is raised it is stored in tanks.
- Gravity moves water through pipes and into homes.
(III) Archimedes Screw
- A screw picks up the water and carries it up to the top of the tube.
- Originally powered by hand, then later by gas or electric motors.
- Leonardo da Vinci later used 2 Archimedes screws to increase efficiency
(IV) Present Day
- Pumps keep the water flowing and are powered by motors.
A tool or device made up of one basic machine.
- There are 6 simple machines that help us do work.
- Each machine has its own advantages and disadvantages.
A rigid bar or plank that can rotate around a fixed point called a pivot or fulcrum.
Enables the user to move a larger load than without.
But the user must move a greater distance than the load.
Determined by the location of the fulcrum and the load being moved.
(I) First class lever – fulcrum between the load and the point of effort.
(II) Second class lever – load is between the effort and the fulcrum.
(III) Third class lever – has the effort between the load and the fulcrum.
2) Inclined Plane:
A flat surface that is at an angle to another flat surface, such as the ground.
- Enables the user to move a larger load than without.
- But the user must move a greater distance than the load.
- The ramp cannot be too steep in order to work.
Similar to an inclined plane, but is forced into an object.
- By pressing on the wide end, the narrow end splits the object.
- Can only be used in one direction, to push objects apart.
- Enables the user to apply a greater force on an object.
- But the user must move a greater distance than the split.
Consists of a cylinder with a groove cut in a spiral on the outside.
- Can penetrate materials using a relatively small force.
- Convert rotational motion to linear motion.
- Most screws move objects very slowly.
Made up of a wire, rope, or cable moving on a grooved wheel.
- May be made up of one or many wheels.
- Can be fixed in place or movable.
6) Wheel and Axle:
Made up of two wheels of different diameters the turn together.
- A longer motion on the wheel produces a shorter more powerful motion on axle.
- Enable the user to apply a greater force on an object.
- But the user must move the wheel a greater distance to apply the force.
- Can also be used to increase speed (ex. Bicycle).
** A simple machine can increase or change the direction of the force that you apply.
But, the cost is that the force the user applies must move farther than the load.
The Complex Machine – A Mechanical Team
Why complex machines?
- As larger communities developed, newer more complicated machines developed.
- New larger energy sources like coal, oil, and electricity combined with new technologies, caused an industrial revolution.
- This led to an increase in people’s standard of living.
- But has also led to people now being dependent on technology.
A system in which simple machines all work together.
A group of parts that work together to perform a function.
- (Ex) bicycle
A smaller group of parts in a complex machine with one function.
- (Ex) braking and steering
Subsystems that Transfer Forces
A belt or chain to transfer energy from a energy source to an object.
- (Ex) bicycle chain
A special type of linkage for transferring energy from the engine to the wheel in large vehicles such as cars or trucks.
- more useful when larger loads must be moved.
A pair of wheels with teeth that interlink; when they rotate together, one gearwheel transfers turning motion and force to the other.
- are important because control the transfer of energy in a system.
- gear wheels work together in gear trains (2 or more gears).
Gear that has original force applied to it.
Gear that receives the force after.
How do gears affect speed?
(I) When driving gear is smaller than the driven gear = The turning speed in the system increases.
- For every turn the larger wheel makes the smaller gear will do many more.
- Are called multiplying gears.
(II) When the driving gear is larger than the driven gear = The turning speed in the system decreases.
- Are called reducing gears.
- In some systems the gears are meshed together, but in some cases they are connected by a linkage.
Understanding of mechanical advantage and work helps determine the efficiency of machines
Understanding simple & complex machines advanced world exploration,
- (Ex) Sail boat
Machines Make Work Easier.
- A winding road is actually a series of inclined planes with switchbacks, which allow cars to drive up a steep hill.
Mechanical Advantage :
Amount by which a machine can multiply a force. Also called the force ratio
Force applied to the machine.
Force the machine applies to the object.
Force is measured in Newtons (N).
Mechanical Advantage (MA) = Force Output (N) / Force Input (N)
Measures the distance an object travels in a given amount of time.
- Speed = Distance (m)/ Time (s)
Measure of how the speed of the object is affected by a machine.
SR describes how much faster the user is moving than the load is working.
- Speed Ratio (SR) Input Distance (m)/ Output Distance (m)
** A machine can increase or change the direction of the force that you apply. But, the cost is that the force the user applies must move farther than the load.
A Mechanical Advantage Less Than 1
Useful for tasks that do not require a large output force.
- (Ex) Bicycle – the output force is used for speed.
The Effect of Friction
- Mechanical Advantage does NOT always equal Speed Ratio.
- Friction can affect MA, but not SR.
- Speed ratio represents the ideal mechanical advantage (No friction).
Friction – force that opposes motion.
- caused by the roughness of surfaces.
- As roughness of a surface increases so does the effect of friction.
- Friction creates HEAT, and must be released to protect the system.
Efficiency – measurement of how well a machine or device uses energy.
- affected by friction.
- most energy lost is unusable (ex. Heat).
Efficiency = ________________
- Most complex machines are very inefficient: waste energy.
Ex) Car – 15% efficient.
2.2 The Science of Work
Work – done when a force acts on an object to make the object move.
- Movement is needed before one can say that work has been done.
- Amount of work done depends on 2 things:
1) amount of force exerted on the object
2) distance the object moved in the direction of the applied force.
Work (N*m) = Force (N) * Distance (m)
- N*m is called a Joule (J)
- The joule is also used in calculating Energy.
Energy and Work
- Energy and work are closely related, can not have one without the other.
Ex) Car – needs energy (gasoline) in order to work (move)
- Machines help us do work by transferring energy.
Work and Machines
- Using a machine does not decrease the amount of work, it decreases the force.
Ex) Work Input = Work Output
- This equation is affected by friction (just like mechanical advantage)
- Here is another way of calculating efficiency.
Efficiency = ________________
2.3 The Big Movers – Hydraulics
- Most machines that move very large objects use a hydraulic system.
Hydraulic system – system that uses a liquid under pressure to move loads.
- device that uses liquids in a confined space to transfer forces.
- works according to Pascal’s Law.
- Before hydraulic systems most construction was done by hand
- Pneumatic systems use gases while hydraulic systems use liquids.
Pressure in Fluids
Pressure – measure of the amount of force applied to a given area.
Pressure Force (N)
(Pa) = _______________
- pressure applied to an enclosed fluid is transmitted equally in all directions through out the fluid.
A Piston Creates Pressure
- Hydraulic systems work because of pistons.
- Piston – is a disk that fits tightly inside a cylinder.
- as the disk moves it either pushes fluid out or draws a fluid in.
- size can vary.
- Hydraulic system is a combination of 2 pistons attached by a flexible pipe.
- Input Piston – used to apply force to the fluid.
- Output Piston – transfers the force to the load
- Pressure exerted equally in the fluid provides the mechanical advantage.
Mechanical Output Force
Advantage = _________________
(MA) Input Force