Mechanical Advantage 1

Transcription

1 Mechanical Advantage 1

2 Mechanical Advantage Another Word for Leverage Ways of Making WORK easier or more efficient. 2

3 Work = Work * = Work = * * * 3

4 Mechanical Advantage Output Input 5 8 N = N 52 N 52 N The Higher the Mechanical Advantage, the Easier it is to Push it. 4

5 Mechanical Advantage Output Input 58 N = N In other words, The bigger the M.A. number, the more leverage you ve got. i.e. M.A. of 4 has more leverage than a M.A. of 1 5

6 Mechanical Advantage Output Input 58 N = N If that doesn t make sense, how about: If you don t have to push as hard to get that thing to move, it s because you ve got more leverage. 6

7 Question What set up will give you the most mechanical advantage with the following simple machines? Levers Pulley s Inclined Planes 7

8 Mechanical Advantage for a 1 st Class Lever Output Input Fulcrum Demo: Shovel or any other lever x = x To give any 1 st class lever extra mechanical advantage, increase the Arm and decrease 8 the Arm by moving the fulcrum.

9 Principle Term Relationship If I I also Which Means I Mechanical Advantage Which Means it Feels Easy (1-2 N) If I I also Which Means I Mechanical Advantage Which Means it Feels Hard (9-10 N) 9

10 = Leverage Class 1 Lever A first class lever is where the force and the weight are at the ends. Fulcrum Demo: Shovel or any other lever x = x To give any 1 st class lever extra mechanical advantage, increase the Arm and decrease 10 the Arm by moving the fulcrum.

11 Class 1 Lever Arm Arm Notice that the effort arms are different lengths. The effort arms that are longer give the scissors more mechanical advantage. In other words, it makes it easier to cut stuff. 11

12 = Leverage Fulcrum & Arm Relationship F = 2N F = 4N F = 10N F = 10N F = 4N F = 2N D = 10cm D = 5cm D = 2cm D = 2cm D = 5cm D = 10cm 12

13 = Leverage Class 2 Lever A second class lever is where the force and the fulcrum are at the ends. Arm Resistanc e Arm Fulcrum x = x To give any 2 nd class lever extra mechanical advantage, increase the Arm and decrease the Arm 13 by moving the object or extending the lever.

14 Class 2 Lever If we were to move the object closer to the wheels, we would give it more mechanical advantage. In other words, it makes it easier to lift stuff. 14

15 = Leverage Class 3 Lever A third class lever is where the force is in the middle. Resistanc e Arm Arm Fulcrum x = x To give any 3 rd class lever extra mechanical advantage, increase the Arm and decrease the 15 Arm by moving the place you put the

16 If we were to move our hands closer to the heads of the sports equipment, we would give it more mechanical advantage. However, there are times we don t want more mechanical advantage we d rather have efficiency. Class 3 Lever In other words, If we are catching a big fish, having more M.A. is great. However, in the case of tennis or golf, sometimes we d rather go for efficiency. 16

17 How the Arm Lengths increase Mechanical Advantage Arm 1 Arm 3 2 If the effort arm is the distance between the fulcrum and the force, and the arm is the distance between the fulcrum and the object To increase Mechanical Advantage for a lever, increase the effort arm or decrease the arm. 17

18 = Leverage How an Incline Plane Works Work = x A ramp works by decreasing the amount of upward force by spreading the work out on the diagonal. 18

19 = Leverage How an Incline Plane Works Work = x 40 cm 30 cm 20 cm Work = x To give this simple machine more mechanical advantage, simply make the ramp longer 19

20 = Leverage What would happen to work if? If I increased the height of the ramp, I did more work than the previous ramp, because I increased the distance, but did not change the weight of the object going up. Work = x If the work is the same as the work, what would happen to the amount of work I did if I increased the height of the ramp? 20

21 = Leverage Wedge s A wedge works like two ramps put together. As the wedge (Ax) goes down, the wedge spreads out the work along the sides which then pushes the wood apart near the top of the wedge. The longer the wedge (blade), the more mechanical advantage. Demo: Ax 21

22 Wheel & Axle When the effort length is extended relative to the resistance length, so is mechanical advantage. Fulcrum Axle Wheel Mechanical Advantage = Length of / Length of 22

23 To give the wheel & axle more mechanical advantage, you can: make the axle smaller, or make the wheel bigger A Wheel & Axel works when you turn the larger cog a longer distance. This means that it requires less force. On the other side, it increases the amount of force because the work is done over a shorter distance. 23

24 Wheel & Axle Mechanical Advantage By increasing the effort arm, I increase the Mechanical Advantage 24

25 Slow Every 1 rotation = 5 rotations On a bicycle, A Change in & in the front cog changes the force and distance on the back cog. Wheel & Axle Fast 25