PuleyPatter MovablePulleys • Build model 7 shown on page 17. Make sure all axles can spin freely. Attach a load to the hook. Predict what happens when you pull on the string. The string lifts the load when you pull on it. The load is easier to 10. However, you have to pull the string farther with a movable pulley than with a fixed pulley.
MainIdea: A movable pulley can he used with a fixed pulley to lift a load with less effort than with a fixed pulley alone.
fixed pulley
AdditionalInformation: A system of a fixed pulley and a movable pulley is called a block and tackle. Sometimes such systems include several pulleys. Because two strings are supporting this movable pulley, you have to pull twice as much string to raise the load compared with the fixed pulley alone. However, you need only half the force.
PulleySummary Pulley wheels connected by a belt turn in the same direction. Wheels connected by a crossed belt turn in opposite directions. The belt may slip. A small pulley wheel makes a large wheel turn slower (gearing down); a large wheel makes a small one turn faster (gearing up). Belts and pulley wheels can be used to change motion through 90 degrees. Pulley wheels of different sizes can be mounted on the same axle for more extensive gearing down or gearing up arrangements. A movable pulley requires less effort to raise an object than a fixed pulley.
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