MachinesMaking Work

Easier

Machines

A device that makes work easier Some powered by engines/motors,

others powered by people

Can you think of some?SIMPLE MACHINE = a device that

does work with only one movementI have some examples…There are 6 types

Advantages of Machines

They make work easier by…1. Multiplying the effort force

2. Changing the direction of the applied force you exert

3. Increasing the distance through which the resistance force moves

4. Overcoming gravity and friction

Applying force and doing work

EFFORT FORCE = the force applied to a machine

RESISTANCE FORCE = the force applied by the machine to overcome resistance

For Review………………

Where is the effort force?

Where is the resistance force?

A

B

C

Applying force and doing work

W = Fd (Work = Force ٠ distance)W = F ٠ dMeasured in Joules (J)You push a box with a force of 200N.

The box moves 1m. How much work did you do?

W = 200N x 1mW = 200J

Applying force and doing work

A girl lifts a 12N (a) weight 1.5m (b) How much work does she do on the weight?

F = d =W = Fd

Applying force and doing work

REMEMBER energy is always conserved so…..

You never get more work out than you put in

Win = Wout (in an ideal machine)

Why will work out always be smaller?

The Simple Machines

http://www.enchantedlearning.com/physics/machines/Levers.shtml

http://www.flying-pig.co.uk/mechanisms/pages/lever.html

LEVERS

A bar that is free to pivot, or turn, about a fixed point

FULCRUM = the fixed point of a leverEFFORT ARM = the part of the lever on

which the effort force is appliedRESISTANCE ARM = the part of the

lever that exerts the resistance force

LEVERS

Teeter-totter, can opener, tennis racket

Helps you do more work with the strength you already have

3 TYPES OF LEVERS

FIRST CLASS = fulcrum is between the effort and resistance forces (teeter-totter) Multiplies the effort force and changes its

direction Effort moves farther than Resistance.

1st Class Lever

When the fulcrum is closer to the effort than to the load: there is a loss in force There is a gain in speed and distance.

1st Class Lever

When the fulcrum is closer to the load than to the effort: there is a loss in speed and distance There is a gain in force.

1st Class Lever

When the fulcrum is midway between the effort and the load: there is no change in force, speed or

distance

3 TYPES OF LEVERS

SECOND CLASS = resistance is located between the effort force and the fulcrum (wheelbarrow) Always multiplies effort force Effort moves farther than Resistance.

3 TYPES OF LEVERS

THIRD CLASS = effort force is located between the resistance force and the fulcrum (fishing pole) Increases speed (cannot multiply the force) Resistance moves farther than Effort. Multiplies the distance the effort force

travels

How well do you know your levers?

A. 1st class B. 2nd class C. 3rd class

Pulleys

A grooved wheel with a rope, chain, or belt running along the groove

Flagpole, blindsThe two sides of the pulley are the effort arm

and resistance armWHAT DOES A PULLEY DO?

changes the  direction of the force makes it easier to lift things to

high-rise areas.There are 3 types of pulleys

Fixed Pulley

A fixed pulley is attached to something that does not move

Changes the direction of the effort force.to pull or push  the pulley up and

down. Disadvantage: have to apply

more effort than the load

Movable Pulley

A movable pulley moves with the load May be attached to a construction crane Does multiply the effort force Cannot change direction of the effort force. Mechanical advantage is the effort

distance divided by the resistance distance.

Disadvantage: have to pull or push the pulley up or down.

Advantage: less  effort to pull the load.

Block and Tackle Pulley

A movable pulley and a fixed pulleythe effort needed to lift the load is less than half

the weight of the load. Advantage: effort is less than

half of the load. Disadvantage: travels a very

long distance.

Wheel and Axle

a lever that rotates in a circle around an axle. Two wheels of different sizes connected -

the axle being the smaller wheel. Larger wheel may be a crank handle or faucet

handle Door knob, water faucet

Wheel and Axle

A GEAR is a wheel with teeth along its circumference

Effort is exerted on one gear to cause the other gear to turn

Inclined Plane

A plane is a flat surface Inclined plane is a plane that is slanted Ramp Used to move things from a lower to higher

place or vice versa

Inclined Plane

How does the amount of work done with a ramp

compare to the amount of work done lifting the object?

Will be the same Force to lift would be

greater than the force use to push

Distance pushed up the ramp would be farther than distance lifted

Screw

an inclined plane wrapped around a cylinder.

Multiplies an effort force by acting through a long effort distance.

The closer the threads on a screw, the greater the mechanical advantage

The plane actually slides through the wood

Wedge

An inclined plane with one or two sloping sides that moves

The wedge used to increase force.  The material remains in place while he wedge

moves through it. A wedge changes the direction of the input

force. Ax, knife, chisels The "sharper" the wedge, the greater the

mechanical advantage. Can be used to split, cut, or fasten

(nail/doorstop)

Compound Machines

A combination of two or more simple machinesLawn mowerPencil sharpenerAxBicycle

Honda - The Cog