1. Lesson 20 Any change that occurs requires energy
Energy is the ability to do
work or cause change

2. Work Work is the application of a force to an object
to move it a certain
distance in the direction
of the force
* Work = force x distance or w= f x d

3. Work Work is not always done when a force is applied to an object
Work is done only when an
object moves in the same
direction of the force that is being applied

4. Work
For example, you may get tired after carrying your backpack all day at school
However, you did not do any
work to carry your backpack
The force you applied was in an
upward direction to keep the
backpack from falling to the
ground

5. Work The backpack moved in a forward, not upward direction
as you walked through school

6. Work Now picture a person wearing a backpack and climbing up the
side of a mountain
The person is doing work because
the direction of motion and the
force being applied are both
upward.

7. Simple Machines A machine is a device that makes work easier by
changing the size or
direction of a force

8. Simple Machines There are six types of simple machines: Lever
Inclined plane
Wheel and axle
Wedge
Pulley
screw

9. Simple Machines Complex machines are made from
a combination of these six simple
machines

10. Inclined Plane An inclined plane is a straight, slanted surface
A ramp is an example of a
stationary inclined plane
An inclined plane makes
work easier because it is easier to push an object up a ramp than it is to lift the same object straight up to the same height

11. Wedges and Screws Wedges and screws are examples of inclined planes
that move
A wedge is an inclined
plane that is wider or
thicker at one end than at
the other

12. Wedges and Screws A wedge makes work easier because, when
moved, a wedge is
used to cut, split, or
pry apart objects

13. Wedges and Screws A screw is an inclined plane
that is wrapped around a
cylinder
When a screw is turned, a
small force is applied over
the long distance of the
screw’s threads

14. Wedges and Screws A screw makes work easier depending on the number
of threads, which in turn
depends on the length of
the inclined plane wrapped
around the center

15. Levers A lever is a simple machine made up of a bar that pivots
at a fixed point called a
fulcrum
The force applied to a lever is
called the effort
The object moved is the load

16. Levers Levers make work easier in three different ways, and levers are
therefore classified into three groups

17. Levers These three groups are based upon the locations of the
fulcrum, effort, and load
In a first class lever, the fulcrum
is located between the effort
and the load

18. Levers In a second class lever, the load
is located between the fulcrum
and the effort
In a third class lever, the effort
is applied between the fulcrum
and the load

19. Pulleys A pulley is a rope or chain wrapped around a wheel
A load is attached to one
end of the rope
A force is applied to the other

20. Pulleys Pulley systems can consist of one or more fixed
pulleys, one or more
moveable pulleys, or both
fixed and moveable pulleys
making a combined pulley
system

21. Wheel and Axles A wheel and axle is a simple machine that
consists of two circular
objects of different
sizes
The wheel is always
larger than the axle

22. Wheel and Axles A wheel and axle makes work easier by getting
more force from the effort
put in when compared to
the amount of distance

23. Wheel and Axles When effort is applied to move the wheel, the axle
turns a shorter distance,
but it moves with a more
powerful force