Pulleys A Pulley is a grooved wheel with a rope, chain, or cable running along the groove Change the direction of an applied force Transmit rotational motion Produce a mechanical advantage in a linear or rotational system of motion Fixed pulleys Movable pulleys Two or more pulleys together = a block and tackle

Common Types of Pulley Systems: Block and tackle Fixed Movable Compound

Fixed pulley A FIXED pulley is attached to something that doesn’t move such as a ceiling or wall A FIXED pulley changes ONLY the DIRECTION of the force. IMA = 1

Movable pulley A MOVABLE Pulley has one end of the rope fixed and the wheel is FREE to move Movable Pulleys multiply force The rope attached to the ceiling supports half of the weight. You need to exert only the other half of the weight to support and lift the weight.

For a Fixed pulley, the distance you pull the rope downward equals the distance the weight moves upward. For a movable pulley, the distance you pull the rope upward is TWICE the distance the weight moves upward

Block and tackle A system of pulleys consisting of fixed and movable pulleys is called a block and tackle

Ideal Mechanical Advantage The IMA of a pulley system is equal to the number of rope segments that support the weight IMA = input distance output distance

What is the IMA of the following pulleys?

Wheel and axle A wheel and axle is a simple machine consisting of a shaft or axle attached to the center of a larger wheel, so that the wheel and axle rotate together Usually input force is applied to the wheel and output force is exerted by the axle

Mechanical Advantage in the Wheel and Axle The greater the diameter of the wheel the more torque is generated on the axle IMA = wheel diameter/ axle diameter

Gears Two or more gears working in tandem are called a transmission Geared devices can change the speed, torque, and direction of a power source. A gear is a wheel and axle with the wheel having teeth around its rim When the teeth of two gears interlock, turning one gear causes the other gear to turn Each rotation of the larger gear causes the smaller gear to make more than one rotation