simple machines, work, power

1. Chapter 5
Simple machines

2. WORK
 The transfer of
energy that occurs
when a force makes
an object move
 In order for work to
be done a force must
make an object move

3. 2 Conditions of work
 1. The object must move
 2. Movement must be in the same direction as
the force applied

5. Work and Energy
 When work is done there is always a transfer
of energy
 Energy is the ability to do work
 When you do work on an object, you increase
its energy

6. Calculating work
 Work (J) = Force (N) x distance (m)
 W = Fd

7. Power
 The rate at which work is done
 SI unit for power is the Watt (W)
 P (watts) = Work (J)/Time (s)
 Usually expressed in kilowatts

8. Power and Energy
 Power is the rate at which energy is transferred
 Power (w) = energy (J)/Time (s)

9. Machine
 A device that makes doing work easier

10. Simple Machines
 A Machine that does
work with only one
movement of the
machine
 6 types of simple
machines: lever, pulley,
wheel and axle, inclined
plane, screw, and wedge

11. Lever
 A bar that is free
to pivot or turn
around a fixed
point
 The fixed point is
called a fulcrum
 There are 3
classes of levers

13. Pulley
 A grooved wheel with a
rope, chain, or cable
running along the
groove
 The axle of the pulley
acts as the fulcrum
 Fixed and movable
 Fixed IMA = 1,
Movable IMA = 2

14. Block and Tackle pulley
 A system of pulleys
consisting of both fixed
and movable pulleys
 IMA is equal to the
number of rope
segments that support
the weight

15. Wheel and Axle
 consists of a shaft or
axle attached to a larger
wheel.
 The wheel and axle
rotate together
 Examples: Pencil
sharpeners, door knobs,
screw drivers, faucet
handles

16. Inclined Plane
 A sloping surface, such
as a ramp.
 Reduces the amount of
force required to do
work
 IMA = Length of slope
(m)/Height (m)

17. Screw
 An inclined plane
wrapped in a spiral
around a cylindrical
post
 IMA is related to the
spacing of the threads

18. Wedge
 An inclined plane with
one or two sloping sides
 It changes the direction
of the input forces

19. Compound Machine
 Two or more simple machines that operate
together
 A car is a compound machine

20. Compound Machines

21. 2-Forces Involved in Work
1. Input Force: The force that is applied to the
machine. (effort force)
Given the symbol Fin
2. Output Force: The force applied by the
machine.
Given the symbol Fout

22. 2-Types of Work done on a Machine
1. Input Work: The work done by you on the
machine.
Given the symbol Win
2. Output Work: The work done by the
machine.
Given the symbol Wout

23. Conserving Energy
 A machine cannot create energy, so…
Wout can never be greater than Win

24. Which means that…
 Wout will always be less that Win …
 because friction changes some of the energy
to heat.

25. Ideal Machine
 A machine without friction.
 Win = Wout

26. Mechanical Advantage
 The ratio of the output force to the input force.
 Can be calculated using the following equation.

27. Efficiency
 A measure of how much of the input work put into a
machine is change into useful output.

28. Efficiency Cont…
• The efficiency of an ideal machine is 100
percent.
• The efficiency of a real machine is always less
than 100 percent.

29. How can machines be made more
efficient???
• by adding a lubricant,
such as oil or grease, to
surfaces that rub
together.