Inertia of Rest is the tendency of a stationary object to continue to remain at rest unless acted upon by an external force. It is a direct consequence of Newton's First Law of Motion. In simple terms, things that are 'lazy' to start moving exhibit inertia of rest.
The Inertia of a body is directly proportional to its mass. A truck (large mass) has much greater inertia than a bicycle (small mass), which is why it takes much longer to stop a truck than a bicycle.
1. Passengers jerk backward when a bus suddenly starts: When a stationary bus suddenly accelerates forward, the seats move forward with the bus, but the passengers' bodies tend to remain at rest due to inertia. This causes them to jerk backward relative to the bus.
2. A tablecloth pulled quickly: If a tablecloth is pulled very quickly from under dishes placed on a table, the dishes tend to stay in their original position due to inertia of rest. The tablecloth moves, but the dishes (nearly) don't.
3. Dust falling from a carpet when beaten: When you beat a carpet with a stick, the carpet moves forward suddenly, but the dust particles embedded in it remain at rest due to inertia. As the carpet moves away from them, the dust falls down.
4. Coins falling into a glass: If a card is placed on top of a glass and a coin is placed on the card, then the card is flicked away quickly, the coin drops straight into the glass because it was at rest and its inertia keeps it in place while the card is removed.
**Inertia of Rest:** Resistance to starting motion (e.g., bus passenger jerking back). **Inertia of Motion:** Resistance to stopping (e.g., a person falls forward when a moving bus stops). **Inertia of Direction:** Resistance to changing direction (e.g., mud flying off a spinning wheel in a straight line).
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Dimensional Formula of Pressure
Dimensional formula of Pressure is [ML⁻¹T⁻²]. Derived from P = F/A. SI unit is Pascal (Pa). Full derivation with examples.
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