Dr. Courtney said:Think about net force. The force of the string on the pulley is -T on the left side and another -T on the right side. The total contribution of the string to the net force is -2T.
thank you very much sir,for replying i understand all those steps,please proceed on like this.Chandra Prayaga said:OK. So, let us go at it step by step. Call the two masses hanging from the ends of the string as m1 and m2. Concentrate on one mass, say m1.
1. There are two forces on m1. The weight, downwards, and the tension in the string, upwards. Agreed?
2. Since the string is pulling m1 up with the tension T, m1 is pulling down on the string with the same force T. Agreed?
3. The tension in the string is the same throughout. (This assumes that the string is massless, and it does not stretch). So the string is pulling up on m2 on the other side, with the same force T. Agreed?
4. So m2 is also pulling down on the string with the force T. Agreed?
5. So there are two forces on the string, each equal to T, and pointing downwards. Agreed?
Let me know if these steps are clear, and if you can continue on your own from here
A string pulley system is a simple machine that uses a rope or cable wrapped around a wheel to change the direction of a force. When one end of the string is pulled, the other end moves in the opposite direction, creating a mechanical advantage.
There are three main types of string pulley systems: fixed, movable, and compound. Fixed pulleys have a stationary axle and are used to change the direction of a force. Movable pulleys have a movable axle and are used to increase the mechanical advantage. Compound pulleys combine fixed and movable pulleys to create an even greater mechanical advantage.
The mechanical advantage of a string pulley system is the ratio of the output force to the input force. It can be calculated by counting the number of strings supporting the load and adding 1. For example, a system with 3 strings supporting the load would have a mechanical advantage of 4 (3+1).
String pulley systems have several advantages, including the ability to change the direction of a force, increase the mechanical advantage, and distribute weight evenly. They are also simple and inexpensive to construct and can be used to lift heavy loads with minimal effort.
The ideal configuration for a string pulley system depends on the desired mechanical advantage and the weight of the load. Generally, a system with more strings will have a higher mechanical advantage, but it will also require more effort to lift the load. It is important to consider the trade-off between mechanical advantage and effort when determining the ideal configuration for a string pulley system.