<< Chapter < Page Chapter >> Page >
F l o a d · r l o a d = F e f f o r t · r e f f o r t 980 N · 0 . 5 m = F e f f o r t · 1 m F e f f o r t = 980 N · 0 . 5 m 1 m = 490 N

The mechanical advantage is:

mechanical advantage = load effort = 980 N 490 N = 2

Since mechanical advantage is a ratio, it does not have any units.

Pulleys

Pulleys change the direction of a tension force on a flexible material, e.g. a rope or cable. In addition, pulleys can be “added together” to create mechanical advantage, by having the flexible material looped over several pulleys in turn. More loops and pulleys increases the mechanical advantage.

Classes of levers

Class 1 levers

In a class 1 lever the fulcrum is between the effort and the load. Examples of class 1 levers are the seesaw, crowbar and equal-arm balance. The mechanical advantage of a class 1 lever can be increased by moving the fulcrum closer to the load.

Class 1 levers

Class 2 levers

In class 2 levers the fulcrum is at the one end of the bar, with the load closer to the fulcrum and the effort on the other end of bar. The mechanical advantage of this type of lever can be increased by increasing the length of the bar. A bottle opener or wheel barrow are examples of class 2 levers.

Class 2 levers

Class 3 levers

In class 3 levers the fulcrum is also at the end of the bar, but the effort is between the fulcrum and the load. An example of this type of lever is the human arm.

Class 3 levers

Exercise

  1. Riyaad applies a force of 120 N on a spanner to undo a nut.
    1. Calculate the moment of the force if he applies the force 0,15 m from the bolt.
    2. The nut does not turn, so Riyaad moves his hand to the end of the spanner and applies the same force 0,2 m away from the bolt. Now the nut begins to move. Calculate the force. Is it bigger or smaller than before?
    3. Once the nuts starts to turn, the moment needed to turn it is less than it was to start it turning. It is now 20 N · m. Calculate the new moment of force that Riyaad now needs to apply 0,2 m away from the nut.
  2. Calculate the clockwise and anticlockwise moments of force in the figure below to see if the see-saw is balanced.
  3. Jeffrey uses a force of 390 N to lift a load of 130 kg.
    1. Calculate the mechanical advantage of the lever that he is using.
    2. What type of lever is he using? Give a reason for your answer.
    3. If the force is applied 1 m from the pivot, calculate the maximum distance between the pivot and the load.
  4. A crowbar is used to lift a box of weight 400 N. The box is placed 75 cm from the pivot. A crow bar is a class 1 lever.
    1. Why is a crowbar a class 1 lever? Draw a diagram to explain your answer.
    2. What force F needs to be applied at a distance of 1,25 m from the pivot to balance the crowbar?
    3. If force F was applied at a distance of 2 m, what would the magnitude of F be?
  5. A wheelbarrow is used to carry a load of 200 N. The load is 40 cm from the pivot and the force F is applied at a distance of 1,2 m from the pivot.
    1. What type of lever is a wheelbarrow?
    2. Calculate the force F that needs to be applied to lift the load.
  6. The bolts holding a car wheel in place is tightened to a torque of 90 N · m. The mechanic has two spanners to undo the bolts, one with a length of 20 cm and one with a length of 30 cm. Which spanner should he use? Give a reason for your answer by showing calculations and explaining them.

Questions & Answers

if three forces F1.f2 .f3 act at a point on a Cartesian plane in the daigram .....so if the question says write down the x and y components ..... I really don't understand
Syamthanda Reply
hey , can you please explain oxidation reaction & redox ?
Boitumelo Reply
hey , can you please explain oxidation reaction and redox ?
Boitumelo
for grade 12 or grade 11?
Sibulele
the value of V1 and V2
Tumelo Reply
advantages of electrons in a circuit
Rethabile Reply
we're do you find electromagnetism past papers
Ntombifuthi
what a normal force
Tholulwazi Reply
it is the force or component of the force that the surface exert on an object incontact with it and which acts perpendicular to the surface
Sihle
what is physics?
Petrus Reply
what is the half reaction of Potassium and chlorine
Anna Reply
how to calculate coefficient of static friction
Lisa Reply
how to calculate static friction
Lisa
How to calculate a current
Tumelo
how to calculate the magnitude of horizontal component of the applied force
Mogano
How to calculate force
Monambi
a structure of a thermocouple used to measure inner temperature
Anna Reply
a fixed gas of a mass is held at standard pressure temperature of 15 degrees Celsius .Calculate the temperature of the gas in Celsius if the pressure is changed to 2×10 to the power 4
Amahle Reply
How is energy being used in bonding?
Raymond Reply
what is acceleration
Syamthanda Reply
a rate of change in velocity of an object whith respect to time
Khuthadzo
how can we find the moment of torque of a circular object
Kidist
Acceleration is a rate of change in velocity.
Justice
t =r×f
Khuthadzo
how to calculate tension by substitution
Precious Reply
hi
Shongi
hi
Leago
use fnet method. how many obects are being calculated ?
Khuthadzo
khuthadzo hii
Hulisani
how to calculate acceleration and tension force
Lungile Reply
you use Fnet equals ma , newtoms second law formula
Masego
please help me with vectors in two dimensions
Mulaudzi Reply
how to calculate normal force
Mulaudzi

Get Jobilize Job Search Mobile App in your pocket Now!

Get it on Google Play Download on the App Store Now




Source:  OpenStax, Siyavula textbooks: grade 11 physical science. OpenStax CNX. Jul 29, 2011 Download for free at http://cnx.org/content/col11241/1.2
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Siyavula textbooks: grade 11 physical science' conversation and receive update notifications?

Ask