4. Testing the variation of pressure with volume
Fig 1
Testing the variation of pressure with volume
Gas under pressure
Pressure gauge (Pa)
To foot pump

5. Gas under pressure
Pressure gauge (Pa)
To foot pump

7. (80, 40)
(160, 20)

10. When a gas expands slowly (inside a closed container )
the pressure decreases quickly at first then less quickly.
Pressure is inversely proportional to the volume
P = ( constant ) x 1 V or
P x V = (constant )
P1 V1 = P2 V2

11. a. P1E = m c θ = 0.20 x 900 x (40-15) P1 x V1 = P2 x V2 2a.
Spot :
Pressure halves
so the volume doubles !
P x V = P x V2
2a.
100, x = , x V2
= , x V2
= V2
50,000
m = V2

12. a. P1E = m c θ = 0.20 x 900 x (40-15) P1 x V1 = P2 x V2 2b.
Spot :
volume halves
so the pressure
doubles !
200,000
P x V = P x V2
2b.
100, x = P x
= P x
= P2
200,000 Pa = P2

13.
Spot :
not so easy this time!
200,000
P x V = P x V2
2c.
120, x V = , x
120,000 x V =
V =
120,000
V = m3

14. So pressure has decreased by 1/3
Spot :
Volume increases by 3x
So pressure has decreased by 1/3
200,000
180,000
P x V = P x V2
2d.
P x = , x
P x =
P =
P = ,000 Pa

15. a. P1E = m c θ = 0.20 x 900 x (40-15) P1 x V1 = P2 x V2 3.
P1 V1 = P2V2
V1 = P2
V P1
120 = P2
P2 = 120 kPa
P x V = P x V2 3.
x ( ) = P x
12, = P x
12, = P2
100
120 kPa = P2

16. When thermal energy has time to leave ( or enter) the system
these pressure and volume changes
are called isothermal changes,
because the gas temperature remains constant
which is a condition for Boyles law.