LEVERS Presented By : Bansari Borda Guided By : Prof. Anant Chakradeo Retail and Exhibition Design Basic Mechanisms Assignment 2
History of levers â€˘
Levers are one of the basic tools; they were probably used in prehistoric times. Levers were first described about 260 BC by the ancient Greek mathematician Archimedes (287-212 BC). Many of our basic tools use levers, including scissors (two class-1 levers), pliers (two class-1 levers), hammer claws (one class1 lever), nutcrackers (two class-2 levers), and tongs (two class-3 levers). Archimedes is said to have remarked of the lever: â€œGive me a place to stand on, and I will move the Earth.â€?
Levers form one of the most important groups of simple machines, devices that enable energy to be used in the most advantageous way. At its simplest a lever is a rigid bar that can be turned freely round a fixed point (known as the fulcrum), and it is surprising what such a simple device can achieve. Given the right conditions a person could, for instance, lift a car on their own.
Three terms need to be explained in discussing levers. The load which is lifted or moved is referred to as the resistance. The force used in moving it is called the effort – both of these may be measured in Newton's. The mechanical advantage is the ratio of the resistance to the effort. Expressed as a formula: mechanical advantage = resistance/effort.
For convenience levers are often divided into three orders or classes: the first, the second, and the third. In fact there is no actual difference in the principles by which they work, and similar calculations can be applied to all of them. The distinctions between them are concerned with the relative positions of the fulcrum, the effort, and the resistance.
Advantages of lever •
The efficiency of a machine is the ratio of the work output to the work input. If the machine is perfect, then all the work (energy) that you put in (the effort) is used to move the load. It would be 100 per cent efficient. In reality, a machine always wastes some energy as a result of friction between its parts. A lever is a rod or bar that turns on a pivot (the fulcrum). The effort applied at one place moves a load at another place via the fulcrum. There are three different types of levers, each with the effort, load, and fulcrum in different places.
Levers are used to: •
increase force and to change the direction of motion
sometimes we use levers without knowing it.
there are levers we use every day.
Mechanical Advantage â€˘
The mechanical advantage of a machine is the amount that it magnifies (increases) a force to overcome a load. Nutcrackers have a mechanical advantage of about five. The force you use to squeeze the handles is magnified five timesâ€” making it strong enough to crack even the hardest nut.
What is a First-Class Lever? â€˘
A first-class lever is a simple machine that lifts a load across a pivot point called a fulcrum. It differs from all other classes of levers because the fulcrum exists between the load and the force that lifts it. A teeter-totter is an excellent example of a first-class lever because it demonstrates how the lever works and is an iconic image from childhood. First-class levers exist in many common locations, such singly in engine pistons or in pairs in scissors and pliers.
Applications of 1st class levers
What is a Second class lever? â€˘
A second class lever is a lever in which the resistance is located between the fulcrum and the effort. A second class lever always increases the effort force. An example of a second-class lever is a wheelbarrow. The fulcrum is the wheel and the resistance in a wheelbarrow is the object being moved while the person pushing the barrow supplies the effort. The resistance arm is the distance from the fulcrum to the object.
Applications of 2nd class levers
What is a Third class lever? â€˘
In a third-class lever, the effort is between the resistance and the fulcrum. A third-class lever always decreases the effort force. An example of a third-class lever is a person's arm. The fulcrum is the elbow, the biceps provide the resistance and the effort is whatever is being lifted. The distance from the elbow to the biceps is the effort arm and the distance from the elbow to whatever one is trying to lift is the resistance arm. A third-class lever is always a disadvantage.
Applications of 3rd class levers
Screw Presented By : Bansari Borda Guided By : Prof . Anant Chakradeo Retail and Exhibition Design Basic Mechanisms Assignment 2
introduction One of the traditional types of simple machine. Like levers, pulleys, and inclined planes, screws are used for raising large loads by the application of quite small efforts. As with al these machines, the distance the large load is raised is small compared with the distance through which the effort moves.
The screw is the only mechanical component that even comes close to the wheel or lever both in frequency of use or value. A screw is a simple machine consisting of a cylinder or cone with a narrow inclined plane or "thread" wound in spiral form along its length. Unless it is a common screw with a tapered shape it is fitted into a nut or receptacle of some kind that has been made with a counter thread or hollow spiral to receive the screw.
Well, technically, a machine can be anything that performs mechanical “work“, therefore even something as insignificant as a screw can be one. Screw systems such as the Archimedes’ screw are the basis of many mechanical devices, including those used for moving water, grain, or even the transporting of fish from one tank to another.
Where Do You Find a Lead Screw? •
Changes rotary movement into linear movement
Significantly increases force
A person can put a little force into turning the handle to move a heavy car.
A simple screw jack comprises a rod in which a square screw thread has been cut, a base plate in which this can rotate, and a block (or nut) through which the screw thread runs.
Jar lids is an amazing application of screw
Examples of common screw head and thread types
Clamp using screw