Chapter 8 Sect. 2 & 3 Simple and Compound Machines Mechanical Advantage and Mechanical Efficiency 1

2 Simple Machines Ancient people invented simple machines that would help them overcome resistive forces and allow them to do the desired work against those forces.

Simple Machines All machines come from six simple machines. They are: Lever Wheel and Axle Pulley Inclined Plane Wedge Screw

Simple Machines A machine is a device that helps make work easier to perform by accomplishing one or more of the following functions: transferring a force from one place to another, transferring a force from one place to another, changing the direction of a force, changing the direction of a force, increasing the magnitude of a force, or increasing the magnitude of a force, or increasing the distance or speed of a force. increasing the distance or speed of a force.

Mechanical Advantage It is useful to think about a machine in terms of the input force (the force you apply) and the output force (force which is applied to the task). When a machine takes a small input force and increases the magnitude of the output force, a mechanical advantage has been produced.

Mechanical Advantage MA = output force input force Ex. If you apply an input force of 5 Newtons to wall with your hammer but the output force is 25 Newtons onto the nail, the machine has a mechanical advantage of 5.

The Lever A lever is a rigid bar that rotates around a fixed point called the fulcrum. The bar may be either straight or curved. Levers are used to apply a force to a load.

The 3 Classes of Levers The class of a lever is determined by the location of the fulcrum, load and input force.

First Class Lever In a first-class lever the fulcrum is located between the input force and the load. Examples of first-class levers include crowbars, scissors, pliers, and seesaws. A first-class lever always changes the direction of force (ex. a downward input force on the lever results in an upward movement of the output force).

Fulcrum is between input and the load. Multiplies output force and changes its direction.

Second Class Lever With a second-class lever, the load is located between the fulcrum and the input force. Examples: nutcrackers, wheelbarrows, doors, and bottle openers.

Load is between fulcrum and input force. Multiplies input force, but does not change its direction

Third Class Lever With a third-class lever, the input force is applied between the fulcrum and the load. Examples of third-class levers include tweezers, hammers, and shovels. A third-class lever does not change the direction of force and it does not increase the input force.

Input force is between fulcrum and load. Does not multiply the input force Multiplies the distance through which the output force is exerted.

Wheel and Axle The wheel and axle is a simple machine consisting of two circular objects of different sizes. The axle is the smaller of the two objects. When either the wheel or axle turns, the other part also turns.

Pulley A pulley consists of a grooved wheel that holds a rope or cable. A load is attached to one end and the input force is applied to the other.. Two kinds: Fixed or movable. They can combine to make a block and tackle. Fixed- CHANGES direction of force, does NOT increase it. Movable- does NOT change direction of force but DOES increase force

Inclined Plane An inclined plane is an straight sloping surface. The inclined plane makes it easier to move a weight from a lower to higher elevation.

Wedge A wedge is a double inclined plane that moves. When you move a wedge through a distance you apply force on an object. Greater distance= greater force. Examples-doorstop, chisels, axe head, knife

19 Screw The screw is an inclined plane wrapped in a spiral.   While this may be somewhat difficult to visualize, it may help to think of the threads of the screw as a type of circular ramp (or inclined plane).

Here is how…

Remember: MACHINES DO NOT “ SAVE ” WORK THEY ONLY MAKE IT A WHOLE LOT EASIER TO DO!!