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Ruijia Zhang

on 3 May 2013

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Transcript of Levers

Class 3 Class 2 Velocity Ratio Mechanical Advantage MA = Load Force (N)
Effort Force (N) Mechanical Advantage There are two ways you an calculate the the mechanical advantage. But the one using the length of the lever arms is only for prediction without friction.
The effort force that you will predict with that formula will always be less than what you actually need since it takes more force to overcome friction. Levers By: Kruti B. and Ruijia Z. Laws of Levers The three types of levers Class 1 Parts of Levers What is a Lever? One of the 6 simple machines used to gain force or change direction Fulcrum - the support, or point of rest in which a lever turns
Load Force - force exerted by the load
Effort Force - the force exerted in order to move the load
Load Arm - the distance from the load to the fulcrum
Effort Arm - the distance from the effort to the fulcrum This class of levers is capable of moving a heavy load with little force. The fulcrum is located inbetween the load force and the effort force. These levers always move a large load only using a small effort force. The fulcrum is at one end. The effort arm is longer than the load arm. Unlike the other two classes of levers, these levers make it difficult to lift things rather than easier. The effort force is exerted in between the load force and the fulcrum. Though more effort is needed for a Class 3 lever, the benefit is that the longer the load arm is the movements are more magnified. MA = Length of Effort Arm
Length of Load Arm Velocity Ratio = Distance Effort Force Moves
Distance Load Force Moves Possible Ways Levers Could be Used On New Earth Connecting Levers Together Levers can also be combined. This is called a linkage. It is where the fulcrum is attached to a fixed point. Where you choose to place each fulcrum affects the movement of the connecting lever(s). Using a linkage, a given input motion and force can be transferred into the desired output motion and force. Some examples of linked levers include: We are certain that there will be levers on new Earth as some levers are objects you use on a daily basis. Levers will also be very helpful on new Earth as in the beginning there will be a lot of construction and levers can help with that. Efficient Levers To find out whether or not a lever mechanism is efficient or not, you use the percentage of efficiency which is: mechanical advantage velocity ratio Percentage efficiency = x 100 Note: You should always get a percentage efficiency of less than 100%. If you did miraculously get 100%, that would mean there was no friction. But in the real world there is friction, and friction always reduces the mechanical efficiency. Bibliography http://www.howstuffworks.com/lever-info.htm
Mechanical Advantage and Efficiency, Nelson Science & Technology 8 Velocity ratio is the relationship between the distance that an effort force moves and the distance that a load force moves Note: this is the benefit of Class 3 levers, their velocity ratio is always less than 1, while class 2 and 3 always have more than 1. Mechanical Advantage MA = Load Force (N)
Effort Force (N) = 80N
4N = 20 Length of Effort Arm
Length of Load Arm 20cm
1cm = = 20 MA = Velocity Ratio Velocity Ratio = Distance effort force moves
Distance load force moves = 10cm
40cm = 1/4 Types of Linkages The four types of linkages are: Reverse Motion Linkage - These linkages reverse the way the load is moving by placing a fixed fulcrum in the center of the connecting lever Can you think of anywhere else you can find levers? The Human Body Levers In the Human Body Push- Pull Linkage - These linkages have two fixed fulcrums, which makes the output move the same way as the input Bell Crank - This linkage helps change the direction of movement by 90 degrees. This linkage has one fixed fulcrum and two moving fulcrums. Bell Crank's are used in the brake of a bicycle
Parallel Motion Linkages - These linkages are used to move things parallel to each other.
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