# Forces: Upthrust and Atmospheric Pressure

## Upthrust

• When an object is immersed in a fluid (either liquid or gas), the fluid exerts an upward force on the object. This is known as upthrust or buoyancy.

• Upthrust is caused by a difference in pressure at different depths in the fluid. At greater depths, fluid pressure is higher.

• The force of upthrust depends on two primary factors: the volume of the fluid displaced by the object and the density of the fluid. An object will float if the upthrust is equal to the weight of the object.

• According to Archimedes’ Principle, the upthrust on an object immersed in a fluid is equal to the weight of the fluid that has been displaced by the object.

## Atmospheric pressure

• Atmospheric pressure refers to the force exerted on a surface due to the weight of the atmosphere above it. It is also referred to as air pressure or barometric pressure.

• Atmospheric pressure decreases with increasing altitude. This is because as you move upwards, there is less atmosphere (and thus less air weight) above you.

• Pressure in fluids, including the atmosphere, can be calculated using the formula: pressure (Pa or N/m²) = force (N) / area (m²)

• High atmospheric pressure generally correlates to calm, fair weather, while low atmospheric pressure can indicate stormy weather.

• Humans are adapted to the atmospheric pressure at sea level, and changes in atmospheric pressure, such as when climbing a mountain or flying, can have physiological effects.

• Measuring atmospheric pressure is crucial in various fields such as meteorology, aviation, and even in predicting natural disasters like hurricanes.