Force, Area & Pressure: Relationship & Applications

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  • 0:04 Pressure vs Force vs Area
  • 1:45 How to Calculate Pressure
  • 3:53 Lesson Summary
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Lesson Transcript
Instructor: Betsy Chesnutt

Betsy teaches college physics, biology, and engineering and has a Ph.D. in Biomedical Engineering

The same force can have a very different effect depending on the area over which it is exerted. In this lesson, learn about the relationship between force, area, and pressure, and how changes in pressure can have some serious consequences,

Pressure vs Force vs Area

Ava and Eva are identical twins who are the same in every way, including their weight. One day, Ava and Eva decide to go for a walk in the snow. They get dressed, and then Ava puts on her favorite red heels. Meanwhile, Eva, who has always been the more practical sister, puts on her snowshoes.

As soon as they step out onto the snow, Ava's heels sink right through while Eva has no trouble walking on top of the snow in her snowshoes! Why did this happen? If Ava and Eva weigh the same and are exactly the same size, why did Ava fall through the snow while Eva did not?

This occurred because even though both girls exerted the same force on the ground, Eva's snowshoes spread that force over a larger area, causing the pressure on the ground to be much less.

Pressure is defined as the force exerted on a surface divided by the area over which that force acts.

pressure definition

Force is measured in units of Newtons (N), named after the famous scientist Isaac Newton. Area is typically measured in units of meters squared (m2). Since pressure is calculated by dividing force by area, it has units of Newtons per meter squared (N/m2), and this unit is given a new name, Pascals (Pa).

1 Pa = 1 N/m2

Because her high heels only have a small area in contact with the ground (or snow), when Ava tried to walk on the snow in heels, all of her weight was pushing on a very small area of the snow, creating a huge amount of pressure and causing the snow to collapse. Meanwhile, Eva's snowshoes spread the same force over a much larger area, so there was much less pressure on the snow. Even though the total force was the same, the pressure was very different, and so there was a very different outcome.

How to Calculate Pressure

We know that Ava's shoes exert more pressure on the ground than Eva's, but how much more? If both girls exert a force of 530 N on the ground, and Ava's shoes have a total area of contact with the ground of only 0.0002 m2, how much pressure does Ava exert on the ground?

To find the pressure exerted by her heels on the ground, divide the force (530 N) by the area (0.0002 m2).

pressure of ava shoes

Wow! That's a lot of pressure! No wonder she fell through the snow.

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