# I Boyle's Law and Applied pressure

#### nmsurobert

Summary
P = F/A and Boyles Law relationship
When using a Boyle's Law Apparatus, pressure applied to the plunger can be calculated by knowing the mass of the object on the plunger and the area of the plunger. P = F/A.

The change of pressure inside the cylinder can be calculated using Boyles Law, P1V1 = P2V2

Should the value for the pressure applied to the top of the plunger be the same as P2, the pressure of the gas in the cylinder once the plunger has been compressed? should P2 = F/A ?

I did some math and math shows that they aren't equal. they're close, but not the same. however, i don't know if they should be equal under ideal conditions. using P = F/A, that value is slightly larger than using P2 = (P1V1)/V2

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#### Chestermiller

Mentor
Summary: P = F/A and Boyles Law relationship

When using a Boyle's Law Apparatus, pressure applied to the plunger can be calculated by knowing the mass of the object on the plunger and the area of the plunger. P = F/A.

The change of pressure inside the cylinder can be calculated using Boyles Law, P1V1 = P2V2

Should the value for the pressure applied to the top of the plunger be the same as P2, the pressure of the gas in the cylinder once the plunger has been compressed? should P2 = F/A ?

I did some math and math shows that they aren't equal. they're close, but not the same. however, i don't know if they should be equal under ideal conditions. using P = F/A, that value is slightly larger than using P2 = (P1V1)/V2
Neglecting the weight of the plunger, if the temperature is constant, the pressure P2 should equal the weight.

#### nmsurobert

Neglecting the weight of the plunger, if the temperature is constant, the pressure P2 should equal the weight.
the weight? numerically, P2 = mg?

#### Chestermiller

Mentor
the weight? numerically, P2 = mg?
Plus the atmospheric pressure. In Boyle's law, one must use the absolute pressure.

#### nmsurobert

Plus the atmospheric pressure. In Boyle's law, one must use the absolute pressure.
I'm taking atmospheric pressure into account. once a mass has been added to the top of the plunger,
P2 = F/A + 101325 N/m2 = (P1V1)/V2?

#### Chestermiller

Mentor
I'm taking atmospheric pressure into account. once a mass has been added to the top of the plunger,
P2 = F/A + 101325 N/m2 = (P1V1)/V2?
Yes, assuming the temperature is constant.

#### nmsurobert

"Boyle's Law and Applied pressure"

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