# How to calculate pressure

You will learn how to calculate pressure when a force is applied to an area with some word problems.

The formula we are going to use is:

Pressure =
F / A

Word problem #1:

A human may apply around 18000 pascals of pressure on the ground.

The weight of an adult elephant can be around 5000 kg. Calculate the pressure applied by this elephant on the ground. How does the pressure compared with that of humans? ﻿

Solution:

We need to do a couple of things here to find the pressure.

First, we need to convert the weight to newtons.﻿

1 kg = 9.8 newtons, so 5000 kg is equal to 5000 × 9.8 newtons.

5000 kg = 49000 newtons

Now we need to get the area of the feet of the elephant.

An elephant foot is usually 40 to 50 cm in length and width.

Pick 45 cm, the area is approximately equal to 2025 cm2

For 4 feet, the area is 8100 cm2

Convert the area to meter squared using the following:

1 centimeter squared = 0.0001 meters squared.

8100 centimeter squared = 8100 × 0.0001 meters squared = 0.81 meter squared

Pressure =
49000 / 0.81

The pressure exerted on the ground by the elephant is 60492 pascals.

To compare the pressure, just do a ratio of the elephant's pressure to human's pressure.

60493 divided by 18000 equals 3.36, so the pressure is about 3 times bigger.

This is not huge compared to humans. Keep in mind that the elephant has 4 feet, which help to increase the area which in turn decrease the pressure.

Problem #2:

The weight of a pencil is 0.01 kg and the pressure the pencil applies to a table is 108.88 newtons per meter squared. Calculate the area of the pencil in contact with the table.

The weight of the pencil in newtons is 0.098 newtons.

If 4 =
24 / 6

Then, 6 =
24 / 4

By the same token,

If P =
F / A

Then, A =
F / P

Then, A =
0.098 / 108.88

Area = 0.0009 meter squared.

0.0009 meter squared = 0.0009 × 10000 centimeter squared = 9 centimeter squared

The 9 centimeter squared makes sense since a pencil can be 18 cm long and 0.5 centimeter wide.

### How to calculate pressure of a car on the ground

The idea here is to get the weight of your car. I will let you do this one with some guidelines.

Some car weight 1500 kg. Then, get the area of the 4 tires in contact with the floor in meter squared. Finally, divide the weight by the area you found. Something similar is done if you wanted to know how to calculate pressure of a book on a table, pressure of your television on a stand, etc...

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