2.1 Lever systems, examples of their use and the mechanical advantages they provide

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1 2.1 Lever systems, examples of their use and the mechanical advantages they provide Learning objectives To understand the 3 different lever class systems To be able to describe the components of each lever system. To be able to explain the mechanical advantage of each of the lever and related movements.

2 Levers How does the body use levers to bring about movement?

3 Levers The joints of our skeleton not only allow movement, they also act as LEVERS. The function of levers are to increase the speed at which a body can move.

4 Levers The human body is a system of levers and pulleys which enables us to move. The joint itself is the fulcrum (Pivot). This fulcrum 'takes the strain' of pulling one near, or away from another bone.

5 Levers The levers rotate around a series of joints. The force is provided by the muscles attached to the bone (think of the muscles acting as pulleys). The resistance comes from body weight and any implement used for sport (e.g. a bat or racquet).

6 Levers Levers consist of three components: 1. Fulcrum (F) - the fixed point or pivot 2. Effort (E) point where the force/effort is applied 3. Load (L) - point where the weight/resistance is coming from

7 Class of lever Levers can be classified as: First class Second class Third class

8 Class of lever First Class This is a lever where the Fulcrum (pivot) occurs between the effort and load. Effort Load Lever Arm Fulcrum

9 Class of lever First Class The head is a good example of the action of a first-order lever in the body when the head and neck are being flexed and extended, as in nodding. Muscles in neck contracting Weight of head Neck joint First class levers can increase both effects of effort and the speed of a body.

10 Class of lever Second Class This lever occurs when the load is between the effort and the fulcrum. Load Lever Arm Effort Fulcrum

11 Class of lever Second Class When you raise up on to your toes you are using a second order lever. Weight of body and gravity Muscle working Ankle joint Second class levers tend to increase the effect of the effort force.

12 Class of lever Third Class This lever occurs when the effort lies between the fulcrum and load. This is very common in human movement Load Lever Arm Fulcrum Effort

13 Class of lever Third Class In terms of applying force this is a very inefficient lever, but it allows speed and range of movement. An example within the body is a bicep curl during flexion. The weight Arm Elbow Bicep muscle Third class levers can be used to increase the speed of a body.

14 Mechanical Advantage The relative efficiency of each of the lever systems is called the mechanical advantage. Use the following equipment to explore how high you can propel the eraser. Effort Load Lever Arm Fulcrum How can the 1st class lever below be adjusted to increase or change how high the load can be propelled?

15 Mechanical Advantage The body s levers can be made even more effective by using rackets, oars, paddles, sticks and bats.

16 Mechanical Advantage These pieces of equipment increase the length of the resistance arm of the lever. This in turn increases the speed at the end of the lever.

17 Effects of a lever on the human body The extent to which a lever can increase speed depends upon the relative lengths of the resistance arm (RA) and effort arm (EA). Load Effort Lever Arm RA - Part of the lever between the fulcrum & the load Resistance Arm (RA) Fulcrum Effort Arm (EA) EA - Part of the lever between the fulcrum & the effort

18 Resistance arm The resistance arm (RA) is the part of the lever between the fulcrum and the resistance. The longer the resistance arm, the greater speed can be generated. Load Effort Lever Arm Fulcrum Resistance Arm (RA)

19 Effort arm The effort arm (EA) is the distance between the fulcrum and the effort; the longer the effort arm Sporting implements are often used such as rackets or bats to increase the length of the effort arm which will increase the force that an object such as a ball is struck. Lever Arm Load Fulcrum Effort Arm (EA) Effort

20 Effort arm However the optimal length of an implement should be determined by the strength of the person handling. e.g. junior tennis rackets have been designed for this purpose.

21 Mechanical Disadvantage Most levers in the body are third class levers where the resistance arm is always greater than the effort arm (mechanical disadvantage). The longer the resistance arm of the lever, the greater the speed at the end of it. So when bowling or passing a ball the performers arm should be fully extended to generate the most force and with the greatest speed.

22 Apply it! What has stuck with you? Label the following levers components. Describe the 3 levers in the body (use diagrams to help illustrate your answer) Levers and mechanical advantage Explain the term mechanical advantage Which class of lever always has a mechanical disadvantage?

23 Practice it! Exam questions 1. Which one of the following describes a second class lever system? (1) A B C D The load is at the right-hand end of the lever The fulcrum is in the middle of the lever The load is in the middle of the lever The load and the fulcrum are at the same point on the lever 2. Label the lever system below (4) Lever class =

24 Practice it! Exam questions 2. Analyse how the following parts of the lever system allow the weight trainer in Figure 5 to lift the weight. (i) Fulcrum (2) (ii) Effort (2)

25 Practice it! Marks Scheme: 1. C 2. One mark for linking bone or muscle to component of lever system and one mark for linking this to its use in the biceps curl to lift the weight. For example: Fulcrum elbow is the fulcrum (1) which allows the arm to bend/flex (1) Effort biceps muscle provide the effort (1) which allows the weight lifter to lift the weight (1) 3. i) Third class lever Load Fulcrum Effort