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When you travel in a bus or a car, your body is in motion, in the direction of the moving bus. When the driver hits the brakes suddenly, your upper body moves forward with a jerk while your lower body remains in its original position. This happens due to a phenomenon known as inertia. Inertia is the property of a physical object by virtue of which it resists the force that attempts to change its velocity. In simple words, an object continues to stay at rest or in motion unless an external force is applied to it.
Types of Inertia
The concept of inertia can be classified into the following types:
Inertia of Rest: A body in the state of rest tends to stay at rest unless an external force moves it from its position. For example, we move backwards when a bus starts moving suddenly.
Inertia of motion: A body in the state of motion tends to stay in motion unless an external force brings it to rest. For example, we move forward when a bus stops suddenly by virtue of inertia of motion.
Inertia of direction: A body moving in a particular direction would not change its direction without the application of an external force. For example, our body tilts when a moving bus takes a sharp turn because our torso tends to stay in motion in a straight line.
Factors Affecting Inertia
The primary factor that affects inertia is the mass of the physical object. Inertia is directly proportional to the mass of the body. The higher the mass, the more would be its inertia. Inertia, therefore, also depends on the density of the object.
Density is a physical quantity that is directly related to mass.
In mathematical terms, 𝝆 = m/V, where 𝝆 is the density, m is the mass, and V is the volume of the object. Hence, for objects with similar volumes, inertia is said to be dependent on their densities too. There is a direct proportionality relation between the two, i.e., the higher the density, more would be the inertia.
Practical Examples of Inertia
Inertia has numerous real-life applications that are listed as follows:
1. Cleaning of carpet: The carpet is cleaned by beating it with a wooden log. The dust falls off the carpet as the carpet moves from its position of rest. This happens due to inertia of rest, as per which the dust on the carpet tends to stay at rest. So, the dust particles stay at rest even when the carpet moves, due to which they get separated from the carpet and fall off.
2. Blood rush: While moving down in an elevator, our body is in the downwards motion. When the elevator suddenly stops, our body tends to stay in the downward motion by virtue of inertia of motion. Due to this, there is a sudden rush of blood from head to toe. It can make people nauseous at times.
3. Cardboard coin experiment: This experiment can be easily performed at home. Place a piece of cardboard on a glass of water and place a coin on the top of the cardboard. All objects are in a state of rest. Now, strike the cardboard to remove it completely from above the glass. The coin would fall into the glass of water. This happens because the coin is still in a state of rest by virtue of inertia.
Conclusion
Newton’s first law of motion introduces the concept of inertia. The law states that the body in motion tends to stay in motion in a particular direction, and the body at rest tends to stay at rest without applying an external force. It is also known as the law of inertia. For inertia, the concept of unbalanced force is important. The velocity of the object would not change unless the force is unbalanced. Inertia explains a lot of daily life phenomena like our torso moving backward when a bus at rest starts moving.
