Define pressure and give the unit of pressure - Leaving Cert Physics - Question 6 - 2005

An instrument commonly used to measure pressure is a manometer. Other options include pressure gauges, bourdon gauges, or barometers, depending on the application.

The layer of air known as the atmosphere is held close to the Earth by the force of gravity. Gravity pulls the air molecules towards the Earth, maintaining the atmospheric layer.

One experiment to demonstrate atmospheric pressure is as follows:

1. Apparatus Required: A glass of water, a piece of cardboard.
2. Procedure: Fill the glass with water and cover it with the cardboard.
3. Observation: Invert the glass; the cardboard holds the water in place, illustrating that the atmospheric pressure is greater than the water pressure, preventing it from spilling out.
4. Conclusion: This experiment shows that atmospheric pressure exerts force on the cardboard, allowing it to hold the water.

When atmospheric pressure is high, we generally experience clear and calm weather, as the air sinks, preventing cloud formation. This often results in sunny days with little wind. Conversely, low atmospheric pressure can result in stormy weather, as rising air can lead to cloud formation and precipitation.

To calculate the pressure exerted on the ground by the elephant, we use the formula: $P = \frac{F}{A}$ Here, the force $F$ is the weight of the elephant, which is 40,000 N, and the area $A$ is the total area of contact: $A_{total} = 4 \times 0.2 \text{ m}^2 = 0.8 ext{ m}^2$ Therefore, $P = \frac{40000 ext{ N}}{0.8 ext{ m}^2} = 50000 ext{ Pa}$

If the elephant stood on just two feet, the contact area would decrease, thereby increasing the pressure exerted on the ground. Since pressure is inversely proportional to the area, with a reduced area, the same force (weight of the elephant) would be distributed over a smaller area, leading to a higher pressure. Mathematically, this can be expressed as: $P = \frac{F}{A}$ where a smaller $A$ results in a larger $P$.