Wheels, Gears, & Pulleys

Wheels, Gears, & Pulleys In many cases, a lever’s motion is restricted. In other words, it cannot continue rotating around and around. Examples: seesaw, wheelbarrow, nail clippers Other simple machines do not have this limitation

Wheels, Gears, & Pulleys

Wheel and Axle a rotating object where the force is applied at some distance from the axis This turning force creates a moment or torque.

Wheel and Axle The effort arm is the distance from the center to the applied force. The resistance arm is the distance from the center to the resistance.

effort arm resistance arm

resistance arm effort arm

Wheel and Axle Any device with a handle that turns in a circular direction is most likely a wheel and axle. Examples: can openers, garden hose reels, fishing rods

Wheel and Axle IMA = effort arm resistance arm

Wheel and Axle God is the creator of the wheel and axle. It is found in created organisms as “simple” as a bacterium.

Wheels, Gears, & Pulleys

Gears Gears are wheel and axle combinations with notches or teeth around the circumference. Note that when two gears touch, they always turn in opposite directions.

Gears The IMA of 2 gears can be determined by the ratio of the number of teeth with the following formula: IMA = resistance gear teeth effort gear teeth

Gears effort resistance IMA = 13 21 = 0.62 increases speed

Gears resistance effort IMA = 21 13 = 1.62 decreases speed

Gears Gears can also change the direction of motion. Ex: differential Gears can be combined into systems that can be very complex. Ex: transmission

Wheels, Gears, & Pulleys

Pulleys A pulley is a wheel with a groove containing a rope or cable.

Pulleys The effort arm length and resistance arm length are the same—the distance from the center to the outside of the pulley.

Pulleys A single fixed pulley has an IMA of 1. Why then would we use it? Because you can use your weight to lift the object.

Pulleys A single moveable pulley has an IMA of 2. The rope is supported at both ends, so only half of the weight is at each end.

Pulleys A group of pulleys working together is called a pulley gang or a block and tackle.

Pulleys To find the IMA of a pulley gang, count the number of ropes which support the load. Do not count the section of rope which supplies the effort. Block and tackles greatly increase the effectiveness or MA of pulleys.

What is the MA of this block and tackle? One Two Three Four

What is the MA of the gears shown, if the smaller gear is the effort gear? 0.4 0.5 2.0 2.5

Which of the following is not a modified form of a wheel and axle? Gear Screw Reel Pulley