After learning this topic, students are expected to be able to:
- Explain the concept of pressure.
- Identify the factors that affect pressure.
- Calculate pressure using the correct formula.
- Explain pressure in solids, liquids, and gases.
- Apply the concept of pressure to everyday life.
- Analyze simple problems related to pressure.
Pressure is the amount of force acting on a certain area.
In simple words:
Pressure tells us how concentrated a force is on a surface.
Pressure depends on two factors:
- Force (F)
- Area of the surface (A)
The greater the force, the greater the pressure.
The smaller the contact area, the greater the pressure.
P = Pressure (Pascal / Pa)
F = Force (Newton / N)
A = Area (square meter / m²)
SI Unit of Pressure
The SI unit of pressure is Pascal (Pa).
Pressure on Solid Objects
High heels have a small contact area.
Therefore:
Small area → greater pressure
This is why high heels can exert a large pressure on the floor.
A sharp knife has a very small contact area at its edge.
Therefore, the pressure is large, making it easier to cut objects.
A nail has a sharp tip with a very small area.
The same force produces greater pressure at the tip, allowing the nail to enter wood.
Snow shoes have a large surface area.
Therefore:
Large area → smaller pressure
This helps prevent a person's feet from sinking deeply into snow.
Example Calculation
A box is pushed with a force of 200 N. The area of contact between the box and the floor is 0.5 m². Calculate the pressure!
Pressure in Liquids
Liquids also exert pressure.
Liquid pressure is the pressure produced by a liquid due to its weight.
Liquid pressure depends on:
- Density of the liquid
- Acceleration due to gravity
- Depth of the liquid
The deeper the liquid, the greater the pressure.
usually
Liquid Pressure in Everyday Life
A. Water Tank
The pressure at the bottom of a water tank is greater than the pressure near the surface.
B. Dam
Dam walls are generally made thicker at the bottom because water pressure increases with depth.
C. Divers
A diver experiences greater water pressure when diving deeper.
D. Bottle with Holes
If a bottle has holes at different heights, water from the lowest hole generally travels farther because the liquid pressure is greater at greater depth.
Pressure in Gases
Gases also exert pressure.
Gas pressure is caused by gas particles colliding with the walls of a container.
Examples:
- Air inside a balloon
- Air inside a bicycle tire
- Air inside a football
- Atmospheric pressure
When gas particles collide with the walls of a container, they produce pressure.
Atmospheric Pressure
Atmospheric pressure is the pressure exerted by the air surrounding Earth.
We usually do not notice atmospheric pressure because our bodies are accustomed to it.
Atmospheric pressure generally decreases as altitude increases.
Therefore:
Higher altitude → lower atmospheric pressure
For example, atmospheric pressure at the top of a mountain is lower than atmospheric pressure near sea level.
Pascal's Law
Pascal's Law states:
Pressure applied to an enclosed liquid is transmitted equally in all directions.
This principle is used in hydraulic machines.
Examples:
- Hydraulic brakes
- Hydraulic lifts
- Hydraulic jacks
- Excavators
Simple Example
A small force applied to a small piston can produce a larger force on a larger piston.
The principle can be expressed as:
Archimedes' Principle
When an object is placed in a liquid, the liquid exerts an upward force on the object.
This upward force is called buoyant force.
According to Archimedes' Principle:
An object immersed in a fluid experiences an upward buoyant force equal to the weight of the fluid displaced by the object.
Applications:
- Ships
- Submarines
- Life jackets
- Hydrometers
Why Can Ships Float?
A ship is made of materials that are generally denser than water, but the ship has a large hollow volume.
This allows the ship to displace a large amount of water.
When the buoyant force is equal to the weight of the ship, the ship floats.
Summary
