Machines

A.  Basics

1.  A machine is a device that makes work easier.

2.  Simple machines work with only one movement.

3.  Work = force x distance

4.  Effort force - the force applied to the machine.

5.  Resistance force - the force applied by the machine to move something.

6.  Work input - the work done on the machine.

7.  Work output - the work done by the machine.

8.  In an ideal machine, work input would equal work output.

9.  Mechanical advantage is the number of times a machine multiplies the effort force.

a.  MA = F(r) / F(e)

b.  MA = ED / RD

B.  The Simple Machines

1.  Levers

a.  Parts

1)  Levers are bars that are free to pivot, or turn, about a fixed point.

2)  The fulcrum is the fixed point.

3)  The effort arm is the part on which the effort force is applied.

4)  The resistance arm is the part that exerts the resistance force.

5)  MA = length of EA / length of RA

b.  Classes of levers

1)  1st class        R

                   --------------------

                            ^         E

2)  2nd class                R         E

                   --------------------

                   ^

3)  3rd class                E         R

                   --------------------

                   ^

2.  Pulleys

a.  Pulleys are grooved wheels with a rope or chain running along the groove.

b.  The MA of a block and tackle (several movable pulleys) is equal to the number of ropes that support the resistance.

3.  Wheel and axle

a.  Two wheels of different sizes that rotate together.

b.  The wheel the effort force is applied to is called the wheel; the axle supports the resistance.

c.  MA = radius of wheel / radius of axle

d.  Gears are modified wheel and axle machines.

4. Inclined plane

a.  Ramps are inclined planes.

b.  MA = length of ramp / height of ramp

5.  Screw

a.  The screw is an inclined plane wrapped in a spiral around a cylinder.

b.  The more threads on the screw, the higher the MA.

6.  Wedge

a.  The wedge is an inclined plane with one or two sloping sides.

b.  The more gentle the slope of the sides of the wedge, the greater the MA.

7.  Compound machines are combinations of two or more simple machines.

C.  Efficiency and Power

1.  Efficiency

a.  A measure of how much of the work put into a machine is changed to useful work put out.

b.  The work put out is always less than the work put in.

c.  Formula:

                             W(out)

               efficiency =  ------ x 100%

                             W(in)

d.  Machines are made more efficient by reducing friction with lubricants.

2.  Power

a.  Power is the rate at which work is done.

b.  Formula:  work / time

c.  Unit:  watt (W) is one joule per second

d.  1 kilowatt = 1000 watts