Levers
Levers have 3 parts: they have a fulcrum, an effort, and a load.
1. The fulcrum is the point that doesn't move from it's spot, it only rotates. Sometimes this is the balancing point. In the picture to the left it is the green triangle.
2. The load is sometimes called the resistance. Either way, it is the weight we are trying to lift or it is the area where we are trying to accomplish something.
3. The effort is the point where force is added. Usually it's where someone will push or pull on the lever.
There are 3 classes of levers. They are different due to what is in the middle of the lever.
The 1st class lever has the fulcrum in the middle
The 2nd class lever has the load in the middle
The 3rd class lever has the effort in the middle
An easy way to remember this is:
F 1
R 2
E 3
Said "F, R, E, 1, 2, 3" It rhymes. It also sort of spells "free".
Lets look at some examples:
1. The fulcrum is the point that doesn't move from it's spot, it only rotates. Sometimes this is the balancing point. In the picture to the left it is the green triangle.
2. The load is sometimes called the resistance. Either way, it is the weight we are trying to lift or it is the area where we are trying to accomplish something.
3. The effort is the point where force is added. Usually it's where someone will push or pull on the lever.
There are 3 classes of levers. They are different due to what is in the middle of the lever.
The 1st class lever has the fulcrum in the middle
The 2nd class lever has the load in the middle
The 3rd class lever has the effort in the middle
An easy way to remember this is:
F 1
R 2
E 3
Said "F, R, E, 1, 2, 3" It rhymes. It also sort of spells "free".
Lets look at some examples:
See if you can get these on your own:
Mechanical Advantage for Inclined planes
Mechanical Advantage is a ratio that shows how much easier a simple machine has made an operation. For an inclined plane all you do is take the hypotenuse of the triangle and divide it by the height. In the picture to the left we have a hypotenuse of 12 meters and a height of 4 meters. So:
Hypotenuse / Height = Mechanical Advantage
12 / 4 = 3
Since mechanical advantage is a ratio, that means there are NO UNITS! We would just say "It has a mechanical advantage of 3."
Hypotenuse / Height = Mechanical Advantage
12 / 4 = 3
Since mechanical advantage is a ratio, that means there are NO UNITS! We would just say "It has a mechanical advantage of 3."
Mechanical Advantage for Levers
To calculate the mechanical advantage of levers, you can use one of 2 formulas.
1. Mechanical Advantage = Effort Distance / Resistance Distance (MA = ED/RD)
This formula is used when you are given meters. The effort distance is the distance from the effort to the fulcrum. In the picture to the left that's dE. The resistance distance is the distance from the resistance (or load) to the fulcrum.In the picture that's dL. Always measure to the fulcrum!
Practice: Suppose dE is 2 and dL is 4. What is the mechanical advantage of this lever?
MA = ED/RD
2 / 4 = 1/2 or 0.5
Important: A good mechanical advantage is above 1. If it's not above one then you are putting in more force than you are lifting. If your mechanical advantage is above 1 then you are putting in less force then the weight you are lifting (which is easier). So our lever from our practice isn't a good lever. Get rid of it.
2. Mechanical Advantage = Output Force / Input Force (MA = OF/IF)
This formula is used when given Newtons. It can also be used with any weight unit (like pounds). Output force is the weight of the object you are trying to lift or move. It's the Load or Resistance. Input force is the force that you put in. It's your effort.
Practice: Suppose your Load is 50 Newtons and you lift it by pushing with 10 newtons of force. What is the mechanical advantage of that lever?
MA = OF / IF
50 / 10 = 5
5 is more than 1 so this is a good lever. (Not to mention you can see that if you push with 10 newtons to lift something that weights 50 newtons, that's a good lever.)
1. Mechanical Advantage = Effort Distance / Resistance Distance (MA = ED/RD)
This formula is used when you are given meters. The effort distance is the distance from the effort to the fulcrum. In the picture to the left that's dE. The resistance distance is the distance from the resistance (or load) to the fulcrum.In the picture that's dL. Always measure to the fulcrum!
Practice: Suppose dE is 2 and dL is 4. What is the mechanical advantage of this lever?
MA = ED/RD
2 / 4 = 1/2 or 0.5
Important: A good mechanical advantage is above 1. If it's not above one then you are putting in more force than you are lifting. If your mechanical advantage is above 1 then you are putting in less force then the weight you are lifting (which is easier). So our lever from our practice isn't a good lever. Get rid of it.
2. Mechanical Advantage = Output Force / Input Force (MA = OF/IF)
This formula is used when given Newtons. It can also be used with any weight unit (like pounds). Output force is the weight of the object you are trying to lift or move. It's the Load or Resistance. Input force is the force that you put in. It's your effort.
Practice: Suppose your Load is 50 Newtons and you lift it by pushing with 10 newtons of force. What is the mechanical advantage of that lever?
MA = OF / IF
50 / 10 = 5
5 is more than 1 so this is a good lever. (Not to mention you can see that if you push with 10 newtons to lift something that weights 50 newtons, that's a good lever.)