Transcript Slide 1
Crowbar •In the past, man invented many simple machines to help him to perform the heavy tasks easily •Levers Do you know that What is the meaning of levers ??? Nutcracker Seesaw Manual broom 1-Are all these machines ( levers) similar in shape and size ??? Soda water opener Pump Wheelbarrow Nutcracker Seesaw Manual broom 2-Are all these machines ( levers) consist Of a rigid bar??? Soda water opener Pump Wheelbarrow Nutcracker Seesaw Manual broom 3-Are all these machines ( levers) made Of the same material??? Soda water opener Pump Wheelbarrow Nutcracker Seesaw Manual broom 4-Are all these machines ( levers) are used to move An object??? Soda water opener Pump Wheelbarrow Nutcracker Seesaw Manual broom 5-Is there a person affects On each machine by a force??? Soda water opener Pump Wheelbarrow Nutcracker Seesaw Manual broom 6-Is there a fixed point , where each machine ( levers ) rotate on ??? Soda water opener Pump Wheelbarrow What does the lever consist of ??? What does the lever consist of ??? What does the lever consist of ??? What is the meaning of levers ??? The lever is: a rigid bar that rotates around a fixed point called the fulcrum and is affected by force and resistance . Importance of levers : •Levers are very important in our daily life.(G.R) •Because, they are used in: 1- Increasing force 4-Moving the force from one place to another 2-Increasing distance 5-Accuracy in performance 3-Increasing speed 6-Avoid dangers 1- Increasing force : Crowbar Wheelbarrow Nutcracker Soda water opener •Some levers conserve (save) effort .(G.R) Because in some levers, we use a small force to make a great effort [as moving a heavy load]. 2- Increasing distance : Some levers allow exerting a force for a small distance to move an object for a longer distance. Ex: A manual broom The manual broom is considered as an increasing distance lever. (G.R) Because, your hand moves a small distance at the upper part of the broom, while its lower part moves a longer distance. 3-Increasing speed : Some levers increase the speed of objects that affect on them . Ex: The hockey bat . 4-Moving the force from one place to another : Ex: The manual broom In the manual broom, the force of your hand moves from the upper part to the lower part of the broom to collect the garbage without bending. 5- Accuracy in performance : Some levers are used to pick up (capture)very small objects . Ex: The tweezers. 6- Avoid dangers : Some levers are used to pick up hot , cold and poisonous materials . Ex: The coal holder. The ice holder. Exercises A)Write the scientific term : 1-The first scientist who described the lever . [……………] 2-A fixed point of a rigid bar . [……………] 3-The rigid bar rotates around a fixed point and is affected by a force and resistance . [……………] 4-A lever allows saving the effort . [……………] 5-A lever allows increasing the distance . [……………] Exercises A)Write the scientific term : 6-A lever allows increasing the speed . [……………] 7-A lever moves the force from one place to another [……………] 8-A lever used to pick up very small objects . [……………] 9-A lever protects our hand from heat . [……………] 10-A lever protects our hand from cold . [……………] Types of levers First- class levers Second- class levers Third- class levers 2-The backbone First – class levers F←O→R 1- The fulcrum is between force and resistance . 2- It is the most popular type of levers in our daily life. 3- Each of Scissors , pliers , pincer and nail clipper are composed of two first levers. Second – class levers O←R→F The resistance is between force and fulcrum . Third – class levers O←F→R •Force is between fulcrum and resistance Comparison between the three types of levers : First – class Second – class Points of levers levers comparisonResistance The middle The fulcrum F ← O→ R O←R→F position Examples - see-saw - crowbar - scissors - scale - pincer - paddle - pump Third – class levers Force O←F→R - nutcrackers - fish pole - wheel barrow - manual broom -bottle opener - sweat holder -stapler - ice holder - coal holder - hockey bat -Tweezers -claw hammer Exercises Classify the following tools according to the type of lever: