Work

and

Machines

What is work?Vocabulary

– Work: force exerted on an object that causes it to move

– Joule: unit of work equal to one Newton-meter

–Mechanical Advantage: the number of times a force exerted on a machine is multiplied by the machine

–Ideal Mechanical Advantage: the mechanical advantage of a machine without friction.

WORK• Is force through a

distance• If force is applied

to an object, and the object moves work has been done

• Force must be in the same direction of object’s motion.

Calculating Work• Work can be determined by the formula

W = Force X DistanceEx: If it takes10N (Newtons) to move an object 10m, 100 J(Joules) of work was done

W= 10N X 10m W = 100J

Input and Output Force

• The force applied to a machine is the input force

• The force exerted by the machine is the output force (resistance force)

• Some output force is Some output force is lost due to friction.lost due to friction.

input

output

Fulcrum

Machines• Are devices that make

work easier by changing the amount of force you exert, by changing the distance which you exert the force, or change the direction of force applied

• Machines do not require an input of electrical energy.

• Machines are not 100% efficient due to friction.

Simple Machines

There are six types of simple machines1) Inclined Plane2) Wedge3) Screw4) Lever5) Wheel and axle6) Pulley

Inclined Plane• A slope or ramp

that goes from a lower to higher level

• Makes work easier by taking less force or effort to lift something a certain distance

• Trade off: the distance the load must be moved would be greater than simply lifting it straight up

The longer the incline (the less steep the incline), the less input force you need to push or pull an objectWork is lost to friction.

Wedge• Device thick at one end

and tapers to a thin edge at the other

• Input force is transferred to the tin edge as an output force

• Less input force needed to do the same work.

• Person applies force to ax handle (input force) Ax splits wood (output force)

Screw

• An inclined plane wrapped around a cylinder

• Input force is applied over a great distance

• EX: Bolts, faucets, jar lids

Levers

Lever• A rigid board or bar

combined with a fulcrum and effort.

• By varying position of load and fulcrum, load can be lifted or moved with less force.

• Trade off: must move lever large distance to move load small distance

1st Class Lever• The fulcrum is

located between the effort and the load

• Direction of force always changes

• Examples are scissors, pliers, and crowbars, elbow

2nd Class Lever• The resistance is

located between the fulcrum and the effort

• Direction of force does not change

• Examples include bottle openers and wheelbarrows

3rd Class Lever• The effort is

located between the fulcrum and the resistance

• Direction of force does not change, but a gain in speed always happens

• Examples include ice tongs, tweezers and shovels

Wheel and Axle• Made of two circular or

cylindrical objects attached to each other

• Larger object is wheel, and smaller the axle

• Wheel and axles multiply force, but force is exerted over a longer distance

Pulley• A rope or chain free to

turn around a suspended wheel

• By pulling down on the rope, a load can be lifted with less force.

• Trade off: no real trade off here; the secret is that the pulley lets you work with gravity so you add the force of your own weight to the rope

A pulley changes the amount and direction of the input force. Force is downward.

Living levers – consists of bones and muscles – tendons and muscles pull on bones, making them work as levers

Machines in the human body