Topic 1: Levers and Inclined Planes Mechanical Systems

A lever is a simple machine that changes the amount of force you must exert to move an object. It consists of: 1. A bar that can move around. 2. A fulcrum, which supports the lever. 3. A load, which is the object that you wish to apply the force to.

The force that you exert on a lever is called the effort force. The distance between the fulcrum and the load is called the load arm. The distance between the effort and the fulcrum is called the effort arm.

Levers are sorted into classes depending on the position of the effort force, the load, and the fulcrum. levers

A Class 1 lever has the fulcrum in between the effort and the load. They are used for power and precision. A Class 2 lever has the load between the effort and the fulcrum. They exert a greater force on the load arm than the effort alone. A Class 3 lever has the effort between the fulcrum and load. Effort is greater than force on load, however it moves the load quickly and greater distance.

Your bones act as levers and your joints act as fulcrums. Most levers in your body are class 3 levers however class 1 and 2 also exist. Human body levers have been replicated in the Canadarm and the space station mobile servicing system. See fig 4.6 A, B, pg 275

What is Work? Work occurs when you are exerting a force on an object that causes it to move. The equation for work is: Work= Force x distance Or W= F x d The units for work are joules (or J) A joule is the amount of work it takes to move a 1N weight 1m.

Example Problem P. 276 A force of 2.0N was exerted on a lever and it moved a distance of 0.6m. Calculate the work. W = F x d W = 2.0N x 0.6m W = 1.2 J

An inclined plane is a ramp that reduces the force you need to exert, to lift something. Input work is the work you put into a machine. I.e. lever Output work is the work the machine does on the load.

Output work is never as great as input work. Machines make work easier because they change the size and direction of the force exerted. They may reduce force but increase distance. Mechanical advantage is the comparison of force produced by a machine, to the force applied to the machine. The smaller the effort compared to the load the greater the mechanical advantage.

Calculating Mechanical Advantage Mechanical Advantage = ___Load Force___ Effort Force Or MA= __F L __ F E Mechanical advantage has no units because it is a ratio.

Example Pg. 278 Suppose you are a passenger in a truck that gets stuck in the mud. You and the drive use a tree branch as a lever to life the truck out of the mud. If you apply an effort force of 500 N to the branch and the truck weights 2500 N, then what is the mechanical advantage of the lever? MA= __F L __ = 2500N = 5 F E 500N The lever has exerted a force 5 times greater than the force you exerted on it. This made the job of lifting the truck 5 times easier.

A mechanical advantage can be less than one. i.e. bicycle. On a lever the longer the effort arm, the less force needs to be applied. Therefore another formula for mechanical advantage is: MA= Effort arm Load arm Example: If the effort arm of the lever in the previous example was 3m and the load arm was 0.3m then what is the mechanical advantage? MA= Effort arm = _3m_ = 10 Load arm 0.3m

Speed is the rate of motion or rate in which an object changes position. Class 1 levers increase your effort force – use to lift heavy objects Class 3 levers exert a force on the load that is smaller than the effort force therefore the force will move the load a greater distance at a faster speed. Ergonomics is designing machines to suit people. Ergonomics is used to prevent problems like carpal tunnel syndrome, which is a disorder caused by swelling wrist bones that squeeze the nerves causing numbness in the first three fingers.