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.