Module 2: LEVERS
Identify levers. Calculate the mechanical advantage of a lever. Calculate forces and lengths related to levers. Distinguish and explain the difference between the three classes of levers. Give real examples of the different types of levers.
1. What is a lever? 2. How many classes of levers are there?
Introduction to Levers
A Lever is one of the most commonly used simple machines. A lever is a rigid bar that is used to transfer force. With a pivot /fulcrum, the lever can be used to change force that is applied (effort) by changing the position of the pivot along the lever. EFFORT, PIVOT (Fulcrum) and LOAD are the three features that are common in every lever.
Load: is the weight or resistance that needs to be overcome. Effort: is the force you apply to the lever. Lever Pivot (Fulcrum): is the point on which the lever balances (or pivots)
What is the mechanical advantage of levers???
The mechanical advantage of a machine is the ratio of the output force produced by a machine to the applied input force.
In a lever, the ideal mechanical advantage (MAi) of a lever is the ratio of the length of the effort arm (L E ) to the length of the load arm (L L).
oad (F L ) Load arm length (L L ) Effort arm length (L E ) Effort (F E ) The amount of effort needed to lift a given load with any lever can be calculated using this formula: Where, F E : Effort force F E x L E = F L x L L L E : Effort arm length F L : Load force L L : Load arm length
1. Calculate the effort needed. 2. Calculate the Ideal Mechanical advantage. 0.4 m 2 m Effort =? 400 N
1. The effort is calculated as follows FE x LE = FL x LL FE x 2m = 400 N x 0.4 m FE = 400 N x 0.4 m / 2 m FE = 80 N 2. The mechanical advantage is calculated as follows : MAi= LE / LL MAi = 2 m / 0.4 m = 5
If the effort arm length is 5 times the load arm length, then the effort force required is 1/5 the load force; i.e. to decrease the effort force, increase the effort arm length.
Now Try to solve this example
Maitha was given the task of moving a table of 600N where the load arm length is 5m and the effort arm length is 10m. a) Calculate the Effort needed. b) Calculate the Ideal mechanical advantage (MAi). 1. The effort is calculated as follows: FE x LE = FL x LL FE x 10m = 600 N x 5 m FE x 10m = 3000 FE = 300 N 2. The mechanical advantage is calculated as follows : MAi= LE / LL MAi = 10 m / 5 m = 2
Find the amount of effort Calculate the mechanical advantage 1. The effort is calculated as follows: FE x LE = FL x LL FE x 2.5m = 250 N x 1 m FE x 2.5m = 250 FE = 100N 2. The mechanical advantage is calculated as follows : MAi= LE / LL MAi = 2.5 m / 1 m = 2.5
Find the amount of load Calculate the mechanical advantage 1. The load is calculated as follows: FE x LE = FL x LL 800N x 4m = FL x 2 m 3200 = FL x 2 m FL = 1600 N 2. The mechanical advantage is calculated as follows : MAi= LE / LL MAi = 4m / 2 m = 2
Find the amount of effort Calculate the mechanical advantage 1. The effort is calculated as follows: FE x LE = FL x LL FE x 2 m = 500 N x 5 m FE x 2m = 2500 FE = 1250 N 2. The mechanical advantage is calculated as follows : MAi= LE / LL MAi = 2 m / 5 m = 0.4
Find the amount of effort Calculate the mechanical advantage 1. The effort is calculated as follows: FE x LE = FL x LL FE x 7 m = 350 N x 2.5 m FE x 7m = 875 FE = 125 N 2. The mechanical advantage is calculated as follows : MAi= LE / LL MAi = 7 m / 2.5 m = 2.8
1. What are the main features that are common in levers? 2. How do you think we can change the amount of force that is applied on the lever?
There are 3 classes of levers: First class Second class Third class
In the first class of levers the Fulcrum (Pivot) is positioned between the Effort and the Load. Load Effort Pivot
Pivot In second class levers the load is positioned between the effort and the fulcrum (pivot). Load Effort
E L L E
In third class levers the effort is positioned between the load and the fulcrum (pivot) Effort Load Pivot
F E L E L
Watch the hammer video and determine which class of lever it is. Identify the pivot, the load, And the effort.
Effort Load Pivot
Watch the can crusher video, and determine which class of lever it is. Identify the pivot, the load, And the effort.
Pivot Load Effort
Refer to the scissors image shown, and determine which class of lever it is. Identify the pivot, the load, And the effort.
Load Pivot Effort
Refer to the wheel barrow image shown, and determine which class of lever it is. Identify the pivot, the load, And the effort.
Load Effort Pivot
Refer to the fishing rod image shown, and determine which class of lever it is. Identify the pivot, the load, And the effort.
Effort Pivot
Refer to the shovel image shown, and determine which class of lever it is. Identify the pivot, the load, And the effort.
Pivot Load Effort
LOAD EFFORT PIVOT
LOAD EFFORT PIVOT
EFFORT PIVOT LOAD
Can you think of other examples?
Determine which class of lever is this? Identify the pivot, the load, and the effort. Calculate the mechanical advantage.
First class Load Effort Pivot
Determine which class of lever is this? Identify the pivot, the load, and the effort. Calculate the mechanical advantage.
Second class Load Pivot Effort
Determine which class of lever is this? Identify the pivot, the load, and the effort. Calculate the mechanical advantage.
Load Third class
Did you know? The human body contains different classes of levers. Can you give an example?
Second Class Lever
Worksheets 1 & 2 (in the module) H.W. Worksheet (found on my Weebly and on PLATO) Search the internet for levers in the human body; select one lever and in your report do the following: 1. Describe that lever and state its class. 2. Upload a sketch or an image of that lever indicating the load, effort, and pivot. 3. Include the link to the source of your information.