Simple Machines Chapter 12 Section 3

Simple Machines There are six basic kinds of simple machines: The incline plane The wedge The screw The lever The wheel and axle The pulley

Inclined Plane An inclined plane is a flat, sloped surface.

How It Works An inclined plane allows you to exert your input force over a longer distance. As a result, the input force needed is less than the output force.

How It Works The input force that you use on an inclined plane is the force with which you push or pull an object. The output force is the force that you would need to lift the object without the inclined plane.

Inc. Plane Mechanical Advantage You can determine the ideal mechanical advantage of an inclined plane by dividing the length of the incline by its height. Ideal mech. advan. = Length of incline Height of incline If the height does not change, the longer the incline, the less input force you need to push or pull an object.

Inc. Plane Mechanical Advantage

Wedge A wedge is a device that is thick at one end and tapers to a thin edge at the other end.

How It Works When you use a wedge, instead of moving an object along the incline plane, you move the inclined plane (the wedge) itself. The wedge exerts an output force at a 90º angle to its slope.

Wedge Mechanical Advantage The ideal mechanical advantage of a wedge is determined by dividing the length of the wedge by its width. The longer and thinner a wedge is, the greater its mechanical advantage.

Screws A screw can be thought of as an inclined plane wrapped around a cylinder. This spiral inclined plane forms the threads of the screw.

How It Works When you twist a screw into a piece of wood, you exert an input force on the screw. The threads of a screw act like an inclined plane to increase the distance over which you exert the input force.

How It Works As the threads of the screw turn, they exert an output force on the wood, pulling the screw into the wood. Friction between the screw and the wood holds the screw in place.

Mechanical Advantage The closer together the threads of a screw are, the greater the mechanical advantage. The ideal mechanical advantage of a screw is the length around the threads divided by the length of the screw.

Wheel and Axle A wheel and axle is a simple machine that consists of two attached circular or cylindrical objects that rotate about a common axis, each one with a different radius. The object with the larger radius is called the wheel the object with the smaller radius is called the axle.

How It Works When the input force is applied to the wheel, the wheel and axle increases your force; however, you must exert your force over a long distance. When the input force is applied to the axle, the input force is exerted over a short distance and the wheel and axle multiplies the distance.

Mechanical Advantage You can find the ideal mechanical advantage of a wheel and axle by dividing the radius of the wheel by the radius of the wheel by the radius of the axle. The greater the ratio between the radius of the wheel and radius of the axle, the greater the mechanical advantage.

Levers A lever is a rigid bar that is free to pivot, or rotate, on a fixed point. The fixed point that a lever pivots around is called the fulcrum.

How It Works Lever rests on the fulcrum Input force is exerted The lever pivots on the fulcrum Output force is exerted

Lever Mechanical Advantage A lever helps you in two ways: It increases your input force It changes the direction of your input force You are able to apply a smaller force than you would have without the lever.

Lever Mechanical Advantage Ideal Mech. Adv. = Distance from fulcrum to input force Distance from fulcrum to output force

First-Class Lever First-class lever always change the direction of the input force. If the fulcrum is close to the output force, these levers also increase force. If the fulcrum is closer to the input force, these levers also increase distance.

First-Class Lever

Second-Class Levers These levers increase force, but do not change the direction of the input force.

Third-Class Lever These levers increase distance, but do not change the direction of the input force.

Pulley A pulley is a simple machine made of a grooved wheel with a rope or cable wrapped around it.

How It Works You use a pulley by pulling on one end of the rope, this is your input force. At the other end of the rope, the output force pulls up on the object you want to move.

How It Works A pulley can make work easier in 2 ways: Can decrease the amount of input force (increases force) Can change the direction of your input force

Types of Pulleys A pulley that you attach to a structure is called a fixed pulley. If you attach a pulley to the object you wish to move, you use a movable pulley. By combining fixed and movable pulleys, you can make a pulley system called a block and tackle

Mechanical Advantage The ideal mechanical advantage of a pulley is equal to the number of sections of rope that support the object.

Simple Machines in the Body Levers Most of the machines in your body are levers that consists of bone and muscles. Wedges Teeth

Compound Machines A compound machine is a machine that utilizes two or more simple machines. The ideal mechanical advantage of a compound machine is the product of the individual ideal mechanical advantages of the simple machines that make it up.