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## PowerPoint Slideshow about ' Six Simple Machines Chapter 4 section 3' - gefjun

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Force

- Any push or pull is defined as a force
- The unit of force is the newton
- 1 pound =4.5 newtons

Work

- A force applied through a distance;
- W= F x d
- units of work are Newton meters (N ● m) but are commonly called Joules

Power

- Power is the measure of work done in a given time.
- The formula for power is:
- P = W/t
- The unit of work is the watt ( J/s)
- Since this unit is very small the Kilowatt is often used = 1000 watts.

Inclined Plane

- Also known as a ramp – a flat sloped surface.
- How it works:
- Allows you to exert your force over a longer distance.
- Input force = force you use to push or pull the object
- Output force = the force you would need to lift the object without the inclined plane
- Output force is equal to the objects weight

Inclined plane - Mechanical Advantage

- IMA = length of incline

Height of incline

Example: if you are loading a truck that is 1 meter high using a ramp that is 3 meters long, the

IMA = 3m / 1m = 3

Therefore: the inclined plane increases the force you exert on the object by three times.

By increasing the length of the incline, the less input force needed to push or pull the object.

Wedge

- A device that is thick at one end and tapers to thin edge at the other end.

Input force

wedge

Output force

Output force

Wedge – How it works

- Instead of moving an object along an inclined plane, you move the inclined plane itself.

Screws

- An inclined plane wrapped around a cylinder
- The threads act like an inclined plane to increase the distance over which you exert an input force.
- The threads exert an output force on the wood, pulling the screw into the wood.
- The friction between the wood and the screw holds the screw in place.
- The closer the threads are the greater the mechanical advantage.

Levers

- A rigid bar that is free to pivot, or rotate, on a fixed point.
- The fixed point that a lever pivots around is called a fulcrum
- 3 classes, based on location of fulcrum,

effort force (E) and resistance force (load) (R)

First class lever

- Fulcrum is in between the effort force and the resistance
- Ex. Scissors, crowbar, car jack, prying the lid using a screw driver

Second class lever

- Fulcrum is at one end, effort is at the other end, the resistance is in between

Ex. Wheelbarrow, a Door, a Nutcracker,

Third Class levers

- Fulcrum is at one end , effort force is close to fulcrum, resistance is at other end
- Almost all sports equipment ex.
- Golf club, baseball bat, lacrosse stick, fishing rod, rake, hockey stick etc.

Mechanical advantage

- Ratio of the output force to the input force
- IMA = ideal mechanical advantage, does not include friction
- IMA Formula=

Effort arm distance (cms)

Resistance arm distance (cms)

Actual Mechanical advantage

- Measures ratio of resistance force to effort force, includes friction
- Formula =

Resistance Force(g)

Effort Force(g)

Mechanical Advantage

- When MA is less than one the machine multiplies speed
- When the MA is greater than one the machine multiplies your effort

Wheel and Axle

- a simple machine made of two circular or cylindrical objects fastened together that rotate about a common axis
- The object with the larger radius is the wheel
- Example: screw driver
- It works because the wheel is larger than the axle, the axle rotates and exerts a large output force.
- The greater the ratio between the radius of the wheel and the axle the greater the mechanical advantage.

Pulley

- A simple machine made of a small grooved wheel and a rope or cable wrapped around it
- Pulley’s decrease the amount of input force needed to lift the object and it can change the direction of the input force.
- Example: raising a flag pole.
- Two basic types:

A. fixed pulley-pulley that is attached to a structure

B. movable pulley- pulley attached to a structure that can move

The ideal mechanical advantage is equal to the number of sections of rope that support the object

Compound machine- utilizes two or more simple machines

- Apple peeler, bicycle

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