Linear Motion Linear motion is the most basic of all motions. Uninterrupted objects will continue to move in a straight line indefinitely. Under every day circumstances gravity and friction conspire to bring objects to rest. Linear motion is measured in two parts. Speed, and direction. Together these make up the velocity. Linear motion, is not often used as a starting point for mechanisms. Click on the links below to find how to convert linear motion to other motion types. Motion

“Rack and Pinion” The rack and pinion is used to convert between rotary and linear motion. The rack is the flat, toothed part, the pinion is the gear. Rack and pinion can convert from rotary to linear of from linear to rotary.rotarylinear The diameter of the gear determines the speed that the rack moves as the pinion turns. Rack and pinions are commonly used in the steering system of cars to convert the rotary motion of the steering wheel to the side to side motion in the wheels. Rack and pinion gears give a positive motion especially compared to the friction drive of a wheel in tarmac. In the rack and pinion railway a central rack between the two rails engages with a pinion on the engine allowing the train to be pulled up very steep slopes. Linear Motion to Rotary Motion

Reflect Linear Motion On the left is a simple pulley. As the rope is pulled down the weight moves up by the same distance. In the compound pulley on the right the rope is wrapped around two pulleys. As the rope is pulled the weight, this time attached to the lower pulley rather than direct to the rope, moves up slower than the speed that the rope is pulled. Corresponding to this reduction in speed is an increase in the force on the weight. The amount of increase in the force depends on how many times the rope wraps round the pulleys. By wrapping the rope several times around the pulleys it is easily possible to lift your own weight off the ground! “Pulleys”

Reflect Linear Motion Belt drives are used transfer rotational motion from one place to another. On the left, both pulleys are the same size. Drive can be transferred by friction of the belt on the pulley or, if required, buy using a toothed belt. Chain drives work in a similar way. By crossing the belt the direction of drive can be changed. On the right two sizes of pulley are used to show how speed of rotation can be changed. “Belt Drives”

Levers are an essential part of many mechanisms. They can be used to change the amount, the strength and the direction of movement. The position of the force and the load are interchangeable and by moving them to different points on the lever, different effects can be produced. The fixed point of the lever about which it moves is known as the fulcrum. In this example the force and the load move in opposite directions. With the force three times closer to the fulcrum them the load lifted is only one third of the force but it move three times as far. “Levers” Reflect Linear Motion

First order lever. Like a see-saw or balance, the load and the force are separated by the fulcrum. As one moves up the other moves down. The amount and the strength of the movement is proportional to the distance from the fulcrum. “Levers” Reflect Linear Motion

Second order lever. A wheel barrow is a second order lever. Here the load is between the force and the fulcrum. This uses mechanical advantage to ease lifting of a large weight. “Levers” Reflect Linear Motion

Third order lever. Here the force is between the fulcrum and the load. Mechanical advantage is reduced but the movement at the load point is increased. “Levers” Reflect Linear Motion