PPT

1. Work Review
- Work = force (N) x distance (m)
- Work is measured in Joules (J) which is a N-m
- For work to be done, the object must move in
the same direction as the force.
- Power = work (J) / time (s)
- Power is measured in watts (W)

2. How machines do work
- Machines make work easier by:
1. Changing the amount of force you exert.
2. Changing the distance over which you exert your
force.
3. Changing the direction of your force
- Mechanical Advantage is the number of times
a machine increase the input force on it.
- Output Force is the force the machine exerts
on an object.

3. - All machines lose work due to friction. The
ones that lose the least amount of work are
said to be very “efficient.”
- Machine Efficiency = x 100%
Work Output
Work Input

4. 6 Simple Machines
Chapter 12 ~ Section 3

5. 1. Inclined Plane
Example: Ramp
Mechanical Advantage =
Length of the incline
Height of the incline

6. 6m
2m
MA = __________

8. 2. Wedge
- A device that is thick at one
edge and tapers (gets
smaller) to a thin edge at the
other end.
Example: Log Splitter

10. - Wedge Mechanical
MA =
3cm
9cm
MA = ______
Length of the wedge
Width of the wedge

11. 3. Screw
- An inclined plane (ramp) wrapped
around a central cylinder.
- Mechanical advantage is calculated by
dividing the length of the thread by
the length of the screw. The thread is
usually much longer than the screw
which gives them a very high
mechanical advantage.

13. - A lever is a rigid bar that is free to pivot, or
rotate, on a fixed point called a fulcrum.
- The mechanical advantage of a lever is
determined by comparing the distance from the
fulcrum your input force is and the distance to
the fulcrum of the resistance. The closer the
resistance is to the fulcrum, the greater the
mechanical advantage.
4. Levers
Input
Force
Resistance

14. 3 Classes of Levers
- Your way to remember which lever is which
type is FREE (or FRE). Which ever lever part is
in the middle determines the class of lever.
- Class 1 has the Fulcrum in the middle.
- Class 2 has the Resistance in the middle.
- Class 3 Has the Effort (input force) in the
middle.

15. Class 1 Lever
- Fulcrum in the middle.
- Ex. See-Saw, Paint can opener, can opener,
crowbar, hammer (when pulling a nail).

17. Class 2 Lever
- Resistance in the middle.
- Examples: wheelbarrow, bottle opener, door.

18. Class 3 Lever
- Effort (input force) in the middle.
- Examples: hockey stick, lacrosse stick, baseball
bat, fishing pole, hammer (when hitting a
nail).

19. 5. Wheel and Axle
- 2 circular or cylindrical objects fastened
together that rotate around a common axis
(both rotate around the same thing). The
larger object is the wheel and the smaller one
is the axle.
Wheel Axle

20. - The mechanical advantage of the wheel and
axle is
MA =
- If the radius of the handle of a screw driver is
1.5cm and the radius of the axle is .3cm, what
is the mechanical advantage?
- MA _______
Radius of wheel
Radius of axle
5

21. 6. Pulley
- A grooved wheel with a rope or
cable wrapped around it.
- The ideal mechanical advantage of a pulley
system is equal to the number of supporting
ropes.
- The last downward pulling rope only changes
the direction of the force.

23. Compound Machines
- Any machine that uses 2 or more simple
machines.
- The mechanical advantage is the PRODUCT of
the individual machines that make it up.

28. $200 Bounty!