Work & Simple Machines
Background Information
Investigation 1: Exploring Force
Have you ever been in a tug of war? You push with your feet against the
ground, and you pull as hard as you can. Pushes, pulls, and lifts are all
known as forces. A FORCE is any push or pull from one object to
another. A SPRING SCALE is a scientific tool that measures force, just
like a scale measures your weight, and a ruler measures how long
something is. You know that the units we use to measure how much
something weights is pounds or ounces and that we might uses inches,
yards or even miles to measure distance. The UNIT that we use to
measure force is called a NEWTON. In this Investigation you will be
introduced to a new word called a load. A LOAD is the object or objects
moved by a force. Think about when your mom or dad does the
laundry. What do they usually call it? A LOAD! It takes your mom or
dad EFFORT to pick up the LOAD of laundry. The effort they are using is
called FORCE. The more clothes they have to wash, the heavier the load
is and the more effort or force they are going to need to use to lift the
laundry basket. We will learn a lot more about force in the next unit.
For now it is important that you know:
 Force is the effort needed to lift or move a load
 As the mass (amount of matter) of a load increases, you need to
use more force to lift it
 A Spring Scale measures the amount of force on a load
 Newton is the unit used to measure force
 All three states of matter (solid, liquid, gas) exert a force
* Exert means to use (strength, ability) OR to cause (force, effort)
Investigation 2: Understanding Work
What is work? Placing boxes on a shelf can be tiring work. You have to
lift the boxes up from the ground to the shelf. Lighter boxes require less
force to move, so it is less work to put them on a shelf. The lowest shelf
is closest to the ground, so it is less work to place boxes there than on
higher shelves. But what do we actually mean when we say work? In
scientific terms, WORK is the use of force to move an object (load) a
certain distance. Work is done when lifting a backpack, sliding a box
across the floor, and pulling a wagon. There are many things that seem
like work but are not. For instance, do you think it is work to hold a ball
over your head? Lifting it there is definitely work, but just holding it
there is not. Why? A force must be applied over a distance in order to
qualify as work. When you lift the ball, you are applying a force over a
distance. When you are holding the ball, you are still applying a force,
but the ball is not moving, so the distance equals zero.
How can we find out how much work was done? We need a FORMULA:
Work = Force X Distance
Let’s say for example you applied a force of 20 newtons to lift a box 1
meter. How much work did you preform? The amount of force and the
distance is given in the problem. You just need to plug those numbers
into the formula and solve.
Work=Force X Distance
20 J = 20N X 1m
The J stands for JOULE. Joules are the unit used to measure work just
like newtons are used to measure force and meters are used to measure
distance.
Now lets say you take some items out of the box to make it lighter. This
time you only need to apply 15 N of force to lift the box 1 meter. How
much work did you preform?
15 J = 15N X 1m
Let’s try one more example. You put all of the items back into the box so
again you must apply 20 N of force to lift the box but this time you only
need to lift it 0.5 m (half a meter). How much work is preformed?
10 J = 20N X 0.5m
It is important that you know:
 Work is calculated using the formula: Work = Force X Distance
 As the distance a load is lifted increases the amount of work
exerted to lift the load increases
 As the mass of a load increases, the force on the load increases
 As the force exerted on the load increases, the work done to lift
the load increases
Investigation 3: Simple Machines- The Pulley
Simple machines make work FEEL easier by changing the direction of
the applied force, decreasing the distance over which the force is
applied, or decreasing the force necessary to do work. However, simple
machines DO NOT CHANGE THE AMOUNT OF WORK that is done.
The force you apply to a machine is called the EFFORT. The force the
machine supplies is called the OUTPUT. And you already know the
object moved by the output is called the LOAD. When the force applied
decreases, this causes an increase in the distance over which the force is
applied. Likewise a decrease in the distance over which the force is
applied results in an increase in the applied force. So although the work
feels easier because of a change in one of the variable (force or
distance), the work done remains the same because of an opposing
change in the other variable.
One simple machine is called a pulley. A pulley is a wheel with two
raised edges so that a rope or string will run along the wheel without
coming off. To lift an object, you attach the load to one side of the rope
and apply a force to the other side. Although neither the force applied
to lift the load nor the distance over which the force is applied changes,
the work being done feels easier because the direction you applied the
force changes.
For example, think of a flagpole. To raise the flag without using a pulley,
you must stand on a ladder, lift the flag up and fasten it to a pole or rope.
By using a fixed pulley, you could stand on the ground and pull down on
one side of the rope (EFFORT ARM) rather than applying a force
upwards to lift the flag. Another example is the blinds in your house or
classroom. You pull down (effort arm) in order to move the blinds
(load) up.
A single fixed pulley does not decrease the force applied or the distance
over which the force is applied, but it does make the work seem easier
by reversing the direction of the applied force. In other words, a pulley
does NOT decrease the amount of work done. It often times makes
work FEEL easier by changing the direction force is applied to the load.
It is important that you know:
 A pulley makes work feel easier by changing the direction force is
applied to a load
 A pulley does NOT decrease the amount of work
 A simple machine often makes work FEEL easier by decreasing
the amount of force needed over a greater distance
Investigation: 4 The Lever
A lever is a bar that rotates around a pivot point called the FULCRUM.
Basically a lever is just a long stick that you push or pull against a
fulcrum to move something. A stick lying on top of a rock is a lever. The
stick is the rotating bar, and the rock is the fulcrum. When you use a
screwdriver to open a paint can, the screwdriver is acting as a lever.
Crowbars, seesaws, scissors, pliers, and a hammer pulling a nail are
examples of first-class levers where the fulcrum is between the weight
and the energy moving the weight (your hand for example).
A wheelbarrow, can opener, door and stapler are all second-class levers
where the fulcrum is at one end and you push on the other end.
A third-class lever has the fulcrum at one end, you push on the middle,
and the weight is at the other end. With a third-class lever, you have to
put in more energy than you would just lifting the weight but you get
the weight to move a longer distance in return. Some examples are a
broom, fishing rod, baseball bat, and our own human arm.
It is important that you know:
 The work done on the effort arm of a lever equals work done on
the load arm
 Changing the position of a fulcrum changes the distance over
which a force is applied and the amount of force exerted on the
effort arm
 As the distance over which a force is applied decreases, the force
exerted to lift the load increases
 As the distance over which a force is applied increases, the force
exerted to lift the load decreases
 The work done on the effort arm of a lever does not change when
the position of the fulcrum changes
Investigation 5: The Inclined Plane
Have you ever climbed a tall hill or mountain? The steeper your path,
the more force it takes you to climb. Many paths wind back and forth to
create a gradual rise that is easier to walk up. This is also seen at the
entrance to many buildings. Ramps are sometimes used in place of
stairs. A RAMP is a type of simple machine called an INCLINE PLANE.
The shorter the (effort) distance, the faster the load can be raised, but it
takes more effort to do so. If you make the ramp less steep, it will have
to be longer, but it will be easier to push the load up it.
It is important that you know:
 Less effort is needed to lift a load using an incline as opposed to
lifting the load vertically
 Changing the length of an inclined plane does not change the
amount of work done when lifting a load a specific height
 As the steepness of an inclined plane increases, the effort needed
to lift the load also increases