1. Unit D Mechanical Systems

2. Machines are tools that help humans do work
Machines help people use energy more effectively.
Machine – device that helps us to do work.
An example of technology developing is a combine harvester.

3. Simple Machines – Meet Human Needs
Early machines
1)      Were very simple devices
2)      Depended on people & animals for their source of energy.
Example: Plow

5. How did earlier civilisations 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.

6. How did earlier civilisations get water to their homes?
(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.

8. How did earlier civilisations get water to their 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 used 2 Archimedes screws to increase efficiency

9. How did earlier civilisations get water to their homes?
(IV) Present Day
Pumps keep the water flowing and are powered by motors.

10. Machines effected transportation

11. Simple Machines
Simple Machine – is a tool or device made up of one basic machine.
There are 6 simple machines that help us do work. (levers, inclined planes, wedges, screws, pulleys, wheel & axle)
Each machine has its own advantages and disadvantages.

12. 1) Levers
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 a lever.
But the user must move a greater distance than the load.
3 types:
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.

13. Gizmo: See Saw torque

19. 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 the plane.
But the user must move a greater distance than the load.
The ramp cannot be too steep in order to work.

21. 3) Wedge 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.

22. 4) Screw
Consists of a cylinder with a groove cut in a spiral on the outside.
Can penetrate and materials using a relatively small force.
Convert rotational motion to linear motion.
Better than nails!
Most screws move objects very slowly. (ex. Archimedes screws)

23. 5) Pulley 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.

25. Gizmo: Pulley Lab

26. 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.

27. Wheel & 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).

29. Effects of Simple Machines
You should be aware:
** 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.
Ex. P. 268 fig

30. http://streaming. discoveryeducation. com/search/assetDetail. cfm

31. Homework!
Check & Reflect
P. 268
1-4