Pulleys and springs

pulleys AND spring - exercise therapy bpt

1. PULLEYS BY-PAYAL TOSHNIWAL A pulley is a simple machine which is used to support the human effort. OR A pulley is a grooved wheel which is rotated about a fixed axis by a rope which passes by it. It is also a form of the wheel and axle.

2. LOAD It is an external force applied to the object . EFFORT Force exerted on the pulley’s rope to lift the load. ROPE Cord that slides on the pulley and is pulled to the lift the load.

3. TYPES OF PULLEYS 1.SIMPLE PULLEY SYSTEM FIXED PULLEY – These are used to alter the direction of the force. The pulley block is fixed and the rope which passes round the wheel is attached to the weight at one end and the effort is applied at the other. It uses more effort than the load to lift the load from the ground. EG.- Patella at knees The patella helps to support the work of quadriceps muscle during its Contraction that allows the extension Of knees

4. MOVABLE PULLEY SYSTEM -- A movable pulley is a pulley that is free to move up and down and used to multiply the applied force. It does not change the direction of the applied force EG.- suspension therapy helps in lifting heavy parts of the body

5. 2.COMPOUND PULLEY SYSTEM A compound pulley is a combination of fixed and moveable pulley. It is sometimes called a combination pulley. It is designed to make the effort less than half the weight of a load. EG.-large sailboats .

6. MECHANICAL ADVANTAGE It is the ratio of the load to the effort. MECHANICAL ADVANTAGE =LOAD/EFFORT The larger the mechanical advantage is the easier it will be to lift the weight(load ). In pulley system the MA depends upon the ropes. More the ropes used over the pulley to lift the load less the effort to be applied.

7. SPRINGS Springs are the elastic bodies that can be twisted , pulled or stretched by some force and return to their original shape when the force is released. In other words it is also termed as resilient member .

8. The Extensibility of a spring- A spring can be elongated by a force applied at one end of it in the direction of its long axis ,the other end of the spring being fixed. The increase in the length of the spring is directly proportional to the magnitude of the applied force used to stretch it. THE WEIGHT OF THE SPRING- It is determined by the material used and thickness of the wire from which it is made and the average diameter of the coils. THE RECOIL OF THE SPRING- when the applied force which stretches the spring is removed and the spring returns to its original length the potential energy stored in it during extension is released as kinetic energy.

9. SPRINGS IN SERIES Springs are said to be in series when they are connected end-to-end or point-to-point. The weight of two equal springs arranged in series is the same as that of a single spring , but the amount the amount of force applied is different. 1/ Keq = 1/K1 + 1/K2

10. SPRINGS IN PARALLEL Springs are said to be parallel when they are connected side-by-side. In this the force applied to both the spring is same.For example when a spring of specific weight is not available two equal springs of half the required weight may be used in parallel to produce the same result. Eg - two 40lb springs arranged in parallel are equal to a single 80lb spring. Keq = K1 + K2