Hooke’s Law states that the force required to compress or stretch the spring is proportional to the distance with which the spring is deformed. It is named after British physicist Robert Hooke. He performed a number of experiments to observe the relationship between the forces applied to a spring and its elasticity. In the year 1660, he stated the law as a Latin anagram for the first time. In the year 1678, he published a paper with the title ‘ut tensio, sic vis’, which means ‘as the extension, so the force’ or ‘the extension is proportional to the force’. Hooke’s law finds its prime application in the study of the elasticity property of a material. It is also helpful in studying the behaviour of the springs. The drawback of Hooke’s law is that it is not universally applicable and tends to fail when the maximum limit of compression or expansion of the elastic material reaches. Another limitation is that it is able to provide accurate results only if the material undergoes a small amount of deformation.
Examples of Hooke’s Law
1. Retractable Pen
The retractable pens are also known as click pens. Usually, a click pen consists of springs that are attached to the top and the bottom of the ink cartridge. A plastic tube is present in between this arrangement, which is fixed in a particular place. The springs attached to the internal mechanical arrangement of the plunger and body cam of a retractable pen work on the Hooke’s principle and are responsible to lock and release the ink cartridge as per the requirement.
2. Recoil of a Toy Gun
The toy gun consists of a spring attached to its back. When the trigger of a toy gun is pressed it releases the toy bullet and quickly gets recoiled with the help of a spring attached to its base. This action of recoiling is based on Hooke’s law.
3. Inflating a Balloon
A balloon is elastic in nature. When the air molecules are blown in it, it expands. Similarly, when it is evacuated, it shrinks in size. The expansion and compression of the balloon depend on the force with which the air is pressed into it; therefore, it works on the basis of Hooke’s law.
A manometer is a device used to measure and indicate the pressure of a liquid. It has a ‘U’ shaped tube fixed to a stand that is equipped with a graduated scale. The tube is half-filled with water. One end of the tube is open while the other end is attached to a funnel through a flexible tube. The mouth of the funnel is covered with an elastic film, which is capable of exhibiting Hooke’s law. When the funnel is dipped in a liquid-filled container, the molecules of the fluid exert pressure on the rubber film. The water present in the tube displaces to one side. The scale attached to the set up indicates the magnitude of pressure presented by the liquid.
5. Spring Scale
A spring scale is a hanging scale that is commonly used by vegetable vendors to weigh vegetables and fruits. It consists of a hook that is suspended with the entity that is to be weighed. The hook is internally connected to two large springs that are fixed to the top of the device with the help of bolts. There exists a gear arrangement in between the two springs which are connected to the dial and pointer. The gear gets shifted as per the weight of the object attached to the hook and the pointer deflects accordingly. Thereby, allowing the graduated scale to point to the accurate weight. The internal mechanical arrangement of the scale consists of springs; therefore, Hooke’s law can be easily seen in action.
6. Balance Wheel of Clock
The balance wheel exhibits a continuous motion with the help of a spring. It helps the needle of the watch to move periodically at a steady rate. The spring is attached to the centre of the balance wheel on one end; whereas, the other end of the spring is fixed. Hence, the balance wheel used in the clock is a prominent application of Hooke’s law.
7. Bathroom Scale
The bathroom scale indicates the weight of the body placed on its surface. It is also known as the floor scale. It consists of a movable graduated dial and a fixed pointer that displays the magnitude of the weight. This dial is attached to an arrangement of a pinion gear and rack. The rack on one end is attached to a lever and to a spring on the other end. The spring and the lever and help the rack to move according to the pressure exerted by the body placed on the scale. The arrangement of the four metal bars present in the device is responsible to transfer the pressure to the main spring. The spring exhibits Hooke’s law, gets pressed down, and allows the lever to move. The lever moves the rack, which further rotates the pinion wheel. Thereby, rotating the dial and display the weight.