This document discusses work, power, simple machines, and compound machines. It defines work as a force acting through a distance, and power as the rate at which work is done. Six simple machines are described: inclined planes, wedges, screws, levers, pulleys, and wheels and axles. Compound machines combine two or more simple machines to make work easier by changing the input force, distance, or direction of force. The mechanical advantage of machines allows work to be done with less input force.

1. Work, Power, and Simple
Machines
 Work
 Power
 Machines
 Simple and Compound Machines

2. Work
 Work is defined as a force acting
through a distance.
 Work=Force x Distance
 W=Fd=Newtons x meters=N-
m=Joule
 A Joule (J) is an amount of work or
energy that is equivalent to applying
a 1 Newton force to an object for a
distance of 1 meter.
 Energy is the ability to do work.

3. Work (continued)
Work= Force (F) x Distance (x)

4. Power
 Power is the rate at which work is
done.
 Power=Work/Time
 P=W/t=Joule/s=Watt
 1 Kilowatt (kW)= 1000 Watts

5. Machines
A machine is a device that makes
work easier.
 Work input is the work that is put
into the machine (the input distance
times the input or effort force).
 Work output is the work that a
machine does (the output distance
times the output or resistant force).

6. Machines (continued)
 Machines make work easier by
changing the input force or distance
or by changing the direction of input
force.
 Work is conserved.
 Theoretically, the work put into a
machine must equal the work that
comes out of a machine.
 In practice this never happens due to
energy being lost to friction.

7. Machines (continued)
A comparison of input work to output
work is called efficiency.
 The efficiency of a machine is equal
to work output/work input.
 Due to friction, no machine is 100%
efficient.
 Machines with the smallest amount
of friction are the most efficient.

8. Machines (continued)
 The mechanical advantage of a
machine is also important to know.
 Mechanical advantage tells how
many times the input force is
multiplied.
 The greater the mechanical
advantage, the less force is required
to do the work.
 This comes at the cost of distance,
however.

9. Simple Machines
 Allmachines are either one or more
simple machine.
 There are 6 simple machines:
 Inclined plane, wedge, screw, lever,
pulley, and wheel and axle.

10. Simple Machines (continued)
 An inclined plane is a flat, sloped
surface like a ramp.
 The longer the inclined plane is, the
less force is needed to raise the
object because of the decreased
slope.
 Therefore, longer inclined planes
with less slope yield greater
mechanical advantages.

11. Simple Machines (continued)

12. Simple Machines (continued)
A wedge is a moving inclined plane.
 Many wedges are made from two
inclined planes stuck together like an
ax.
 The longer and thinner the wedge,
the greater its mechanical
advantage.

13. Simple Machines (continued)

14. Simple Machines (continued)
A screw is an inclined plane wrapped
around a central bar to form a spiral.
 A screw gets its mechanical
advantage from the length of the
inclined plane wrapped around it.
 The closer together the threads on a
screw, the greater its mechanical
advantage.

15. Simple Machines (continued)

16. Simple Machines (continued)
A lever is a rigid bar that is free to
pivot about a fixed point called a
fulcrum.
 A good example is the see-saw.

17. Simple Machines (continued)

18. Simple Machines (continued)
 There are three classes of levers.
 A first class lever has a fulcrum in
the middle.
 A second class lever has the
resistance in the middle.
 A third class lever has the effort in
the middle.
 Just remember FRE.

19. Simple Machines (continued)

20. Simple Machines (continued)
 Notice that different classes of levers
change the direction of the input
force.
 This can sometimes make work
easier.
 The mechanical advantage of a lever
is generated by changing the length
of the force or effort arm relative to
the resistant arm of the lever.

21. Simple Machines (continued)
A pulley is a rope, belt, or chain
wrapped around a wheel.
 A fixed pulley can change the
direction of input force.
 Pulleys can be combined in systems.
 The mechanical advantage of a
moveable pulley system is equal to
the number of lifting lines.

23. Simple Machines (continued)
A wheel and axle is a simple machine
made from two circular objects of
different sizes.
 The wheel is the larger of the two.
 The mechanical advantage of a
wheel is generated by the difference
in the radii.

25. Compound Machines
A compound machine is a
combination of two or more simple
machines.