16-­‐11-­‐14 The Pulley Simple Machines: (2) The Pulley (3) The Wheel and Axle Lesson 15 The Wheel and Axle A pulley is made of a grooved wheel with a rope or cable looped around it; the pulley is free to spin. The pulley itself can either be fixed or can move. You will see examples of pulleys in flagpoles (fixed) and in gym equipment (fixed and movable). The IMA of the Pulley A wheel and axle is made of a shaO or axle aPached to a larger disk, called a wheel. You will see examples of wheels and axles in bike pedals, doorknobs, and screwdrivers. Since a fixed pulley only changes the direcTon of a force, its IMA is 1. Moveable pulleys, where one end of the rope is fixed and the pulley/s are allowed to move, spread the weight of the object between the support ropes that exist. The IMA of moveable pulleys is equal to the number of its support ropes. The IMA of the Wheel and Axle An Example Depending on whether the input force is applied to the wheel or the axle, the mechanical advantage will be greater than or less than 1, respecTvely. The handle of a garden tap of radius 3.0cm is connected to a shaO of radius 0.50cm. What is the IMA of the wheel and axle? Input force applied to the axle: ra / rw Input applied to the wheel: rw / ra 1 16-­‐11-­‐14 One More Example You want to design a doorknob that has an output force twice that of the input force. If the radius of the doorknob’s axle is 1.85cm, what does the radius of the doorknob’s handle need to be? If you were to actually measure the output force, why wouldn’t it be double the input force? Your Turn •  Take jot notes from pp136-­‐138 (not collected, but know for unit test) The Inclined Plane Lesson 16 An inclined plane is a sloping surface on which an object can move. An inclined plane decreases the input force required by increasing the input distance required. The same amount of work is ulTmately done, but it is more spread out, e.g., running 1km in 5min or walking 1km in 15min. The IMA of the Inclined Plane The Screw Simple Machines: (4) The Inclined Plane (5) The Screw (6) The Wedge IMA = length of the ramp / height of the ramp What is the ideal mechanical advantage of a ramp that is 3m long and 50cm high? A screw is based on an inclined plane. A screw is an inclined plane wrapped around a rod. This conTnuous inclined plane is called the thread. Just like an inclined plane, the greater the length of the thread, relaTve to its height, the greater the screw’s mechanical advantage. 2 16-­‐11-­‐14 The Wedge A wedge is also based on an inclined plane. A wedge is an inclined plane that travels through another object. The longer and narrower the wedge, the greater its mechanical advantage. Mechanisms A mechanism is two or more simple machines working together. Your Turn •  Take jot notes from pp139-­‐140 –  Not collected, but complete it to prepare for the unit test •  Use pp131-­‐140 to answer quesTons 1-­‐7 on p143 3