Work and MachinesChapter 5 Sec 2

What is a Machine?

Any device that makes work easier.

How do machines make work easier?

Increase force Work = Force X Distance

If force is increased then distance will decrease Ex. car jack

How do machines make work easier?

Increase distance Ex. Ramp

How do machines make work easier?

By changing the direction of the force being applied.

Ex. Car jack, wedge (ax), and pulley

Work done by machines

Force applied to machine is input force.

Output force is the force applied by machine to overcome resistance.

Work done by machines

Law of conservation of energy – energy is always conserved Amount of energy of the machine transfers to the

object cannot be greater than the amount of energy transferred to the machine1. Some energy transferred will be changed to heat due

to friction

An Ideal Machine with no friction and would have the same input work and output work.

Work in = Work out

Win = Wout

Fin x din = Fout x dout

Example: suppose a hammer claw moves a distance of .01 meters to remove a nail. If the output force of 1,500 Newtons is exerted by the claw of the hammer, and you move the handle of the hammer .05 meters, you can find the input force needed.

The Mechanical Advantage

Mechanical advantage (MA) is the number of times a machine multiplies the effort force. It is calculated by MA equals resistance force divided by effort force.

mechanical advantage = output force / input force

MA = __Fout__ Fin

Efficiency

Efficiency is the measure of how much of the work put into a machine is changed into useful output work by the machine

Efficiency = __Output work__ x 100 Input work

Efficiency of a machine is always less than 100%

Efficiency

Lubricants can make machines more efficient by reducing friction.

Simple MachinesChapter 5 Section 3

Simple machine

A machine that does work with only one movement is a simple machine.

Lever

A lever is a bar that is free to pivot about a fixed point called the fulcrum

Input arm - part of lever on which effort force is applied

Output arm – part of the lever that exerts the resistance force.

Classes of levers

First-class Second-classThird-class

Pulleys A pulley is a

grooved wheel with a rope, chain, or cable running along the groove.

Three types of pulleys

1. fixed pulley – attached to something that doesn’t move

2. movable pulley – end of rope fixed and wheel is free to move

3. Block and tackle – system of pulleys consisting of fixed and movable pulleys

Wheel and Axle

Wheel and axle – machine with two wheels of different sizes rotating together; modified lever form

Wheel and Axle

Wheel and axle – machine with two wheels of different sizes rotating together; modified lever form

Gears are a modified form of the wheel and axle

Inclined Plane

Inclined Plane – sloping surface that reduces the amount of force required to do work Less force is required if a ramp is longer and less

steep.

Screw

Screw is an inclined plan wrapped in a spiral around a cylindrical post

Wedge

An inclined plan with one or two sloping sides is a wedge.

Compound machine

A compound machine uses a combination of two or more simple machines.