Simple Machines

Machine: an object that changes either the magnitude or direction of a force

Simple Machines

There are six simple machines: • lever• inclined plane• wedge• wheel & axle• pulley• screw

All other machines are made out of simple machines.

Machines make life easier.

Without simple machines there would be no other

machines.

Mechanical Advantage(how machines make life easier)

e

r

F

FMA

Double a force by using a machine

with a mechanical advantage of two!

effort force (Fe): the force exerted on a machine

resistance force (Fr): the force exerted by a machine

EfficiencyWork is input (Wi) to a machine when an effort force (Fe)

is applied over a distance (de).

Wi = Fede

100% W

Wefficiency

i

o

Work is output (Wo) from a machine when it exerts a resistance force (Fr) over a distance (dr).

Wo = Frdr

Ideal Machines(perfect machines)

r

e

d

dIMA

Ideal Mechanical Advantage

input work (Wi) = output work (Wo)

efficiency = 100%

No real machine is perfectly efficient!

Lever(a rigid object pivoting on a fulcrum)

Three types of levers: • 1st class lever: fulcrum between Fe & the load• 2nd class lever: the load between Fe & the fulcrum• 3rd class lever: Fe between the load & the fulcrum

Fe

load

Fr

Fe

load

Fr

load

Fr

Fe

1st class lever 2nd class lever 3rd class lever

Lever Examples

Crowbar(1st Class Lever Example)

Fe

Fr

Wheel & Axle

Wheels rotate around an axle.

Wheel Examples

Well Wheel

Fe

Fr

Pulley

A pulley is a wheel with a rope running over it

Pulley Examples

Inclined Plane

• A slanted surface or ramp

• Reduces the force required to move objects

Inclined Plane Examples

Wedge

• A wedge is usually a triangle shape with a sharp point.

• A wedge is used to split, secure, or lift.

• Applying a force to one end pushes the wedge between something

• The pictured wedge is designed to split wood when hit with a sledge hammer

Wedge Examples

Wedges that split:• teeth• knives• zippers

Wedges that secure:• doorstops• nails

Wedges that lift:• shims• golf wedges

Screw(a helical inclined plane)

A screw is an inclined plane twisted around an axis.

Screw Examples

All 6 Simple Machines

Lever

Pulley

Wheel & Axle

WedgeScrew

Inclined Plane

Compound Machines

Compound Machine: two or more linked simple machines

The mechanical advantage of a compound machine is the product of the component simple machines’ mechanical

advantages.

Notes: 7. Machine: an object that makes transferring energy easier by changing either the magnitude or direction of a force A. effort force (Fe): the force exerted on a machine B. resistance force (Fr): the force exerted by the machine C. mechanical advantage (MA): the ratio of the resistance force to the effort force

i. e

r

F

FMA

D. input work (Wi): the work done to the machine i. Wi = Fede

E. output work (Wo): the work done by the machine i. Wo = Frdr

F. 100%x W

Wefficiency

i

o

G. ideal (perfect) machines i. input work (Wi) = output work (Wo) ii. ideal efficiency = 100%

iii. ideal mechanical advantage (IMA): r

e

d

dIMA

8. Simple Machines A. lever: a rigid object pivoting on a fulcrum B. wheel & axle: a wheel turning around an axle C. pulley: a wheel with a rope running over it D. inclined plane: a ramp E. wedge: a sharp triangular object F. screw: an inclined plane wrapped around a shaft

9. Compound Machines A. two or more linked simple machines B. MA = (MAmachine 1)(MAmachine 2) (…)

Your Turn

Chapter 10 Practice Problems (p. 238): 13-16