Mechanical Systems Unit

Simple Machines

Machine – a device that helps us perform a task What is a machine? Machine – a device that helps us perform a task

Machines can: Change energy from one form to another Ex. Car Engine Chemical energy in Kinetic energy out

Machines can: Transfer forces Example: Car transmission Transmits force from the engine to the axle/wheels

Machines can: Change the direction of force Example: Raising a flag Pull down on the string, flag goes up

Machines can: Change the magnitude of forces Example: Gears in a Bike Allows you to apply less force over a greater distance to climb a hill

Machines can: Change distance and speed Example: Bike transmission Allows you to apply a smaller force over a greater distance or a greater force over a smaller distance

Lever Type Incline Plane Type Two Types of Machines Lever, pulley, wheel and axle, gears Incline Plane Type Incline plan, wedge, screw

The Lever Family

Fundamental Concept We can reduce the amount of force we need to apply by pulling over a greater distance We can increase the amount of force we apply by pulling over a smaller distance

Definitions Lever – a rigid bar that can rotate freely about a pivot point (or fulcrum) Fulcrum – A pivot point that the lever can rotate about

What does a lever do? Levers turns your effort into a force on a load Effort Force Load Force

Where are the load and effort forces?

Fulcrum is in the middle, load and effort to either side Classes Of Levers 1st Class Lever Fulcrum is in the middle, load and effort to either side

Load is in the middle, fulcrum and effort to either side Classes Of Levers 2nd Class Lever Load is in the middle, fulcrum and effort to either side

Effort is in the middle, fulcrum and load to either side Classes Of Levers 3rd Class Lever Effort is in the middle, fulcrum and load to either side

Remember 1 2 3 F L E

Terminology Effort force (FE) – a force applied to a lever (N) Load force (FL) – a force exerted on a load (N) or a force used to do something

Terminology Effort distance (dE) – the distance from the fulcrum to the effort (m) Load distance (dL) – the distance between the load and the fulcrum (m)

Lever Powered Bike

Identify the Type of Lever

Levers that don’t look like levers… Don’t think a lever is always an unbendable bar It can be something that acts like an unbendable bar! Take a look

Pulleys

Wheel and Axle

Gears

Biology’s Levers

Pulleys Pulley Systems – Machines that move objects with less force Pulley – A wheel that rotates around a fulcrum in it’s centre

Examples

Pulley Systems Pulley systems allow you to pull with less force over a greater distance The advantage provided by the pulley is based on the number of support strands on the mass

For example, the following pulley would require you to pull with half the force over twice the distance

Pull with ¼ the force over 4 times the distance

Wheel and Axle A large circular disc (wheel) with a small rigid rod (axle) through the centre Oldest wheel and axle is around 5000 years old

The Wheel and Axle

Gears Toothed wheels of different diameters

Worm Gear

The Inclined Plane

Inclined Plane Increases the load that can be moved with a given force Makes the force less because the inclined plane supports some of the weight of an object (easier than lifting vertically)

Examples of an Inclined Plane Ramp Stairs – it’s easier to climb stairs than a ladder Easier to push a piano up a ramp than to lift it onto a truck

Wedge A double inclined plane (axe, door stop) Increases applied force and changes it’s direction Transforms a lateral force into a splitting force

A twisted inclined plane (road around a mountain) Screw A twisted inclined plane (road around a mountain) Changes turning force into vertical force

Made of two or more simple machines Compound Machine Made of two or more simple machines

Work Pg 76 # 6,7 Pg 77 # 1,5,6