Contents
Key Stage 3
Meaning
Pressure is the force on a surface per unit area.
About Pressure
- Pressure is measured in Pascals (Pa).
- A large force on a small area causes a large pressure.
- A small force on a large area causes a small pressure.
Equation
- Pressure = (Force)/(Area)
\[P = \frac{F}{A}\] Where:
Example Calculations
| A hydraulic press is used to stamp metal. The press provides a force of 1000N over an area of 0.0002m2. Calculate the Pressure applied by the press. | A 25000N elephant stands on 4 feet. The area of each foot is 0.01m2. Calculate the pressure on one foot. | A person wearing stilettos rests their entire weight of 600N on one heel. The heel has an area of 0.0005m2. Calculate the pressure due to the heel of the stiletto. |
|
F = 1000N A = 0.0002m2 \[P = \frac{F}{A}\] \[P = \frac{1000}{0.0002}\] \[P = 5,000,000Pa\] |
F = 25000N Area of 1 foot = 0.01m2 Area of 4 feet = 0.04m2 \[P = \frac{F}{A}\] \[P = \frac{25000}{0.04}\] \[P = 625,000Pa\] |
F = 600N A = 0.0005m2 \[P = \frac{F}{A}\] \[P = \frac{600}{0.0005}\] \[P = 1,200,000Pa\] |
Pressure in a Fluid
- The force responsible for pressure in a fluid is the weight of all the particles above the object.
- The pressure in a fluid decreases with height and increases with depth. The deeper into a fluid the greater the pressure.
- Since pressure increases with depth then the bottom of an object will experience more pressure than the top of the object. This causes a force called upthrust.
Key Stage 4
Meaning
Pressure is the perpendicular force on a surface per unit area.
About Pressure
- Pressure is measured in Pascals (Pa).
- A large force on a small area causes a large pressure.
- A small force on a large area causes a small pressure.
Equation
- Pressure = (Force)/(Area)
\[P = \frac{F}{A}\] Where:
Example Calculations
| A hydraulic press is used to stamp metal. The press provides a force of 1100N over an area of 0.00023m2. Calculate the Pressure applied by the press correct to two significant figures. | A 25000N elephant stands on 4 feet. The area of each foot is 0.012m2. Calculate the pressure on one foot correct to two significant figures. | A person wearing stilettos rests their entire weight of 630N on one heel. The heel has an area of 0.00029m2. Calculate the pressure due to the heel of the stiletto correct to two significant figures. |
| 1. State the known quantities
Force = 1100N Area = 0.00023m2 |
1. State the known quantities
Force = 25000N/4 = 6250N per foot. Area = 0.012m2 |
1. State the known quantities
Force = 630N Area = 0.00029m2 |
| 2. Substitute the numbers into the equation and solve.
\[P = \frac{F}{A}\] \[P = \frac{1100}{0.00023}\] \[P = 4782608.696Pa\] \[P \approx 4800000Pa\] |
2. Substitute the numbers into the equation and solve.
\[P = \frac{F}{A}\] \[P = \frac{6250}{0.012}\] \[P = 520833.3Pa\] \[P \approx 520000Pa\] |
2. Substitute the numbers into the equation and solve.
\[P = \frac{F}{A}\] \[P = \frac{630}{0.00029}\] \[P = 2172413.793Pa\] \[P \approx 2200000Pa\] |
Pressure in a Fluid
- The force responsible for pressure in a fluid is the weight of all the particles above the object.
- The pressure in a fluid decreases with height and increases with depth. The deeper into a fluid the greater the pressure.
- Since pressure increases with depth then the bottom of an object will experience more pressure than the top of the object. This causes a force called upthrust.