# Pressure

Pressure is like the amount of that push or squeeze spread out over an area. So, if you push down hard with your hand on a small area of the table, you create more pressure than if you spread out your hand and push down with the same force. It's like comparing poking something with your finger versus pressing it with your whole hand.

Pressure

## What is density?

Density is a measure of how much mass is packed into a certain volume of space. Imagine two boxes, one filled with feathers and the other with rocks. Even if both boxes are the same size, the box with rocks will feel heavier because the rocks are more densely packed compared to the feathers.

Pressure is affected by the density of the substance involved. Imagine diving into a pool. The deeper you go, the more pressure you feel. This is because there's more water above you pushing down, and water has a certain density. The deeper you go, the more dense the water becomes due to the weight of the water above pressing down on it. This increase in density leads to an increase in pressure.

## What is upthrust?

Upthrust, also known as buoyancy or buoyant force, is a force that pushes objects upward when they are submerged in a fluid (a liquid or a gas). It's the force that makes objects float in water or rise when placed in a fluid.

When an object is placed in a fluid, if the upthrust force acting on it is greater than its weight (the force pulling it downward due to gravity), the object will float. If the upthrust force is less than its weight, the object will sink. And if the upthrust force and weight are equal, the object will remain suspended in the fluid, neither sinking nor rising - this is what we call neutral buoyancy.

## Key Words

Atmospheric pressure - created on a surface by air molecules colliding with the surface.

Altitude - height above Earth.

Also see Forces, Motion, Force and motion