1. CHAPTER 8 MACHINES

2. Machines make work easier by changing the force you exert in
size or direction, or both.
But it does not change the
amount of work done.
A machine is a device that
makes work easier.

3. Types of Machines Lever Inclined Plane Pulley Wheel and Axle Wedge
Screw

4. Are a combination of two or more simple machines.
Do work
with one
movement
COMPOUND MACHINES
Are a combination of two or more simple machines.

5. MACHINES SIMPLE MACHINES COMPOUND MACHINE Inclined Plane Screw Wedge
TYPE
LEVER
TYPE
AXE
Inclined
Plane
Screw
Wedge
Lever
Wheel
& Axle
Pulley
Wedge
and
Lever

6. VARIABLES
EFFORT FORCE (Fe) is the force you exert on a machine * RESISTANCE FORCE (Fr) is the force applied by the machine to overcome resistance. * EFFORT DISTANCE (de) is the distance moved by the effort force. * RESISTANCE DISTANCE (dr) is the distance moved by the resistance force.

7. VARIABLES
WORK INPUT (Win) is the work put into the machine
WORK OUTPUT (Wout) is the work that the machine puts out.

8. IDEAL MACHINE

9. MECHANICAL ADVANTAGE (MA) is the number of times a machine multiplies the effort force.
IDEAL MECHANICAL ADVANTAGE (IMA)

10. EFFICIENCY
An ideal machine has an efficiency of 100%. Machines have efficiency of < 100%

11. Machines make work easier by changing the force you exert in size and/or direction.

12. LEVERS
A lever is a bar that is free to pivot, or turn, about a fixed point.
The fixed point of a lever is called the fulcrum.
EFFORT FORCE
RESISTANCE FORCE
FULCRUM

13. LEVERS
The part of the lever on which the effort force is applied is called the effort arm.
The part of the lever that exerts the resistance force is called the resistance arm.
EFFORT ARM
RESISTANCE ARM

14. LEVERS
EFFORT ARM
RESISTANCE ARM

15. FIRST CLASS LEVER
The fulcrum is always in between the effort force and the resistance force. Examples: seesaw, hammer, hair clip, bottle opener, crow bar and cart

16. FIRST CLASS LEVER EFFORT FORCE EFFORT ARM RESISTANCE ARM
RESISTANCE FORCE

17. SECOND CLASS LEVER
The resistance is located between the effort force and the fulcrum. They always multiply effort force.
Examples: nutcracker,
wheelbarrow, hole puncher,
bottle opener, lemon squeezer

18. SECOND CLASS LEVER EFFORT FORCE EFFORT ARM RESISTANCE ARM
RESISTANCE FORCE

19. THIRD CLASS LEVER
The effort is located between the resistance force and the fulcrum. They do not multiply effort force.
Examples: rake, broom,
fishing pole, your arm, and
hockey stick

20. THIRD CLASS LEVER EFFORT FORCE RESISTANCE ARM EFFORT ARM
RESISTANCE FORCE

21. THIRD CLASS LEVER Effort arm is always shorter than
EFFORT FORCE
RESISTANCE ARM
EFFORT
ARM
RESISTANCE FORCE
Effort arm is always shorter than
the resistance arm, so it cannot
multiply force. It’s MA is
always less than 1.

22. LEVERS WITH A HUMAN TOUCH
First Class Lever
Your neck muscles support the effort force to hold up the resistance weight of your head.
Second Class Lever
Tip of your feet-Fulcrum
Weight -Resistance
Muscles- Effort

23. LEVERS WITH A HUMAN TOUCH
Third Class Lever
Elbow-Fulcrum
Biceps-Effort
Weight-resistance R E F

24. PROBLEM #1
A lever uses a force of 250 N to move a rock that weighs 3000 N. Find the mechanical advantage of using the lever.

25. PROBLEM #3
A simple machine allows a worker to move an effort distance 45 cm in order to move a resistance distance 20 cm. What is the ideal mechanical advantage of the machine?

26. PULLYING WITH PULLEYS
A pulley is a grooved wheel with a rope or a chain running along the groove. A pulley works something like a first class lever. Instead of a bar a pulley has a rope. The axle of the
pulley acts like the fulcrum. The two sides of the pulley
are the effort arm and the resistance
arm.

27. SINGLE FIXED PULLEY
It is lifted the same distance as it is pulled at the other end of the rope.
Example: flagpole, blinds.
Force is not multiplied. There is only a change in the direction of the force applied. W F

28. SINGLE MOVABLE PULLEYS
Force is multiplied.
IMA = 2, since two wires
are supporting the
resistance. The effort
distance must be twice
as large as the resistance
distance.
Example:construction
cranes. F W

29. BLOCK AND TACKLE It is combination of fixed and movable pulley.
It can produce large
enough force to lift
automobiles.

30. WHEEL AND AXLE Wheel and axle is a simple machine consisting
of two wheels of different sizes that rotate together.
Examples: doorknob, faucets, handles,
steering wheel of a car etc.
An effort force is applied to the larger wheel. The smaller wheel, called the axle, exerts the resistance force.
It allows us to use less force to do work.

31. WHEEL AND AXLE
Gear is a modified wheel and axle machine. It is wheel with teeth along its circumference. Effort is exerted on one of the gears and the other gear turns.

32. INCLINED PLANE
Slanting boards and ramps are called inclined planes. They are sloping surfaces used to raise objects. W=weight, H=height, L=length, F=force L H F W

33. L H F W

34. PROBLEM #5
What is the ideal mechanical advantage of a ramp 4 cm long and 2 cm high?

35. PROBLEM #8
What is the efficiency of a machine with work input 1000 J and work output 700 J?

36. ramp that runs from its tip to
SCREWS
Screw is another form
of inclined plane. The
threads form a tiny
ramp that runs from its tip to
near its top. As you turn the screw, the threads seem to pull the screw into the wood.

37. When a screw is turned , it moves forward. At the
SCREWS
When a screw is turned ,
it moves forward. At the
same time, it presses
against the material around it. Many turns are needed to move the screw a short distance. But the screw produces a far greater force than the force needed to turn it.

38. a moving inclined plane. The material remains in one place while the
WEDGE
Wedge is a form of
inclined plane. It is
a moving inclined plane.
The material remains in
one place while the
wedge moves through it.
Examples: blade of an axe, knife blade, razor blade, door stop, chisel.