Homework 2 Levers
The lever is a basic mechanism used in a multitude of different situations in many machines
and tools, such as typewriters, crowbars, spanners etc. Levers are simple mechanisms and
involve an effort and a load working about, or around, fulcrum (also known as a pivot). Most
but not all levers are designed to increase force (measured in Newtons) and provide
mechanical advantage to make something easier.
There are 3 types of lever, all of which are shown below.
THE FIRST CLASS LEVER
In this lever the effort is one end of the lever, the load the opposite and the fulcrum is
somewhere in the middle. The basic principle of this type of lever is the following:
1. The longer the distance between the effort and the fulcrum the less effort required
moving or lifting a load.
2. The shorter the distance between the load and the fulcrum the less effort required
moving or lifting a load.
3. Lever is in equilibrium when the effort x distance of effort from fulcrum is equal to
the load x distance of load from the fulcrum
Case Study - Scissors
Notice that the handle of the scissors are two levers which have a fulcrum between the
applied force and the load. This layout means the scissors are first class levers. The applied
force is where the fingers are pushing inwards on the handles. The load is at the blades
where they meet to cut material. It may look like the position of the fulcrum is not closer to
the load, but it depends on where along the blades you cut the material. Moving the load
(material to cut) closer to the fulcrum makes it easier to cut. Cutting something close to the
fulcrum puts the load closer, so you get more mechanical advantage (multiplied force). This
allows you to cut through thicker material. if the blades are doing the cutting at their tips of
the scissors, you don't get this advantage and it makes it more difficult (more force is
required) to cut the material.
THE SECOND CLASS LEVER.
In this lever the fulcrum is at the end of the lever, the load is somewhere along the length of
the lever and the effort is applied at the opposite end to the fulcrum.
Basic Principle:
1. A class two lever allows a large load to be lifted by a smaller effort. Because the load
is always closer to the fulcrum, the effort is always less than the load.
Case study - Nutcracker
A nut cracker uses a pair of second class levers. We know these are second class levers
because the fulcrum is at one end, and the applied force is at the other. The load is in
between. You get more mechanical advantage if you place the nut closer to the fulcrum
than to your hand. The closer it is, the more your force gets multiplied.
THE THIRD CLASS LEVER.
With a class 3 lever, the fulcrum is at one end, the load is at the other and the effort is in the
middle. A class three lever allows a small load to be lifted by a larger effort.
Basic Principle:
1. Because the effort is always closer to the fulcrum, the load is always less than the
effort, but the load always moves through a larger distance than the effort.
Case Study – Lifting Objects
Your arm is a third class lever. The fulcrum is at the elbow, and the load is what you have in
your hand. The force is applied somewhere in between by a muscle attached above the
fulcrum, on the upper arm.
Questions on Levers
Q1 The unit used to measure the amount of force (effort) needed to lift/move a load is the
A. kilogram
B. volt
C. distance
D. newton
Q2 A class 3 lever has the _________ in the middle.
A. effort
B. load
C. fulcrum
Q.3 A class 2 lever has the _____ in the middle.
A. effort
B. load
C. fulcrum
Q.4 A class 1 lever has the _____ in the middle.
A. effort
B. load
C. fulcrum
Q.5 In class 1 levers, the effort increases as the load moves closer to the fulcrum.
A. true
B. false
Q.6 In class 2 levers, the effort decreases as the load moves closer to the fulcrum.
A. true
B. false
Q.7 In class 3 levers, the effort decreases as the load moves farther from the fulcrum.
A. True
B. False
Q.8
What kind of lever system is a hockey stick?
A. Class 1
B. Class 2
C. Class 3
D. A hockey stick is not a lever.
Q.9 A crowbar is a class _____ lever.
A. 1
B. 2
C. 3
D. 4
Q10 an increase in force obtained by using a lever is called
A. velocity ratio
B. mechanical advantage
C. interval
D. effort