Pressure (P1.3) | OCR GCSE Physics A (Gateway Science) — Higher (J249)

P1.3 Pressure

Summary This section develops the understanding of pressure in gases and liquids. Pressure in gases builds on the particle model, and in liquids the increase in pressure with depth is explained as the weight of a column of liquid acting on a unit area. Underlying knowledge and understanding Learners should be aware of the change in pressure in the atmosphere and in liquids with height (qualitative relationship only). They should have an understanding of floating and sinking and the effect of upthrust. Learners should know that pressure is measured by a ratio of force over area which is acting at a normal to the surface.

Common misconceptions Learners commonly have misconceptions about floating and sinking, based on the premise that light or small objects float and heavy or large objects sink. They often misunderstand the role of pressure difference and suction e.g. the collapsing can experiment and the forcing of air into the lungs during inhalation.

Reference	Mathematical learning outcomes	Mathematical skills
$PM1.3i ☑$	$pressure (Pa) \times {volume (m}^{3}) = constant$

Learning outcomes	To include	Maths	Working scientifically	Practical suggestions
$P1.3a explain how the motion of the molecules in a gas is related both to its temperature and its pressure$	$application to closed systems only$	$M1c, M4a, M5b$	$WS1.1b, WS1.2a, WS1.2e, WS1.3e, WS1.4a, WS2a$	$Demonstration of the difference in pressure in an inflated balloon that has been heated and frozen. (PAG P1) Building manometers and using them to show pressure changes in heated/cooled volumes of gas. (PAG P1)$
$P1.3b explain the relationship between the temperature of a gas and its pressure at constant volume (qualitative only)$		$M1c, M5b$	$WS1.1b, WS1.2a, WS1.2e, WS1.3e, WS1.4a, WS2a$	$Demonstration of the exploding can experiment. Building of Alka-Seltzer rockets with film canisters.$
$P1.3c ☑ recall that gases can be compressed or expanded by pressure changes and that the pressure produces a net force at right angles to any surface$		$M4a, M5b$	$WS1.1b, WS1.2a, WS1.2e, WS1.3e, WS1.4a, WS2a$	$Compressing syringes containing sand, water and air. (PAG P1) Demonstration of the collapsing can experiment. Demonstration of the Cartesian diver experiment.$
$P1.3d ☑ explain how increasing the volume in which a gas is contained, at constant temperature can lead to a decrease in pressure$	$behaviour regarding particle velocity and collisions$	$M1c, M4a, M5b$	$WS1.1b, WS1.2a, WS1.2e, WS1.3e, WS1.4a$	$Demonstration of the behaviour of marshmallows in a vacuum.$
$P1.3e ☑ explain how doing work on a gas can increase its temperature$	$examples such as a bicycle pump$		$WS1.1b, WS1.2a$	$Demonstration of heat production in a bicycle inner tube as it is pumped up.$
$P1.3f ☑ describe a simple model of the Earth’s atmosphere and of atmospheric pressure$	$an assumption of uniform density; knowledge of layers is not expected$	$M5b$
$P1.3g ☑ explain why atmospheric pressure varies with height above the surface of the planet$
$P1.3h ☑ describe the factors which influence floating and sinking$
$P1.3i ☑ explain why pressure in a liquid varies with depth and density and how this leads to an upwards force on a partially submerged object$			$WS1.1b, WS1.2a, WS1.3a, WS2a$	$Discussion of buoyancy of a ping pong ball in water.$
$P1.3j ☑ calculate the differences in pressure at different depths in a liquid$	$knowledge that g is the strength of the gravitational field and has a value of 10 N/kg near the Earth’s surface$	$M1c, M3c$	$WS1.1b, WS1.2a$	$Demonstration of differences in water pressure using a pressure can with holes.$

Learning outcomes

To include

Maths

Working scientifically

Practical suggestions

P1.3a explain how the motion of the molecules in a gas is related both to its temperature and its pressure

application to closed systems only

M1c, M4a, M5b

WS1.1b, WS1.2a, WS1.2e, WS1.3e, WS1.4a, WS2a

Demonstration of the difference in pressure in an inflated balloon that has been heated and frozen. (PAG P1) Building manometers and using them to show pressure changes in heated/cooled volumes of gas. (PAG P1)

P1.3b explain the relationship between the temperature of a gas and its pressure at constant volume (qualitative only)

M1c, M5b

WS1.1b, WS1.2a, WS1.2e, WS1.3e, WS1.4a, WS2a

Demonstration of the exploding can experiment. Building of Alka-Seltzer rockets with film canisters.

P1.3c ☑ recall that gases can be compressed or expanded by pressure changes and that the pressure produces a net force at right angles to any surface

M4a, M5b

WS1.1b, WS1.2a, WS1.2e, WS1.3e, WS1.4a, WS2a

Compressing syringes containing sand, water and air. (PAG P1) Demonstration of the collapsing can experiment. Demonstration of the Cartesian diver experiment.

P1.3d ☑ explain how increasing the volume in which a gas is contained, at constant temperature can lead to a decrease in pressure

behaviour regarding particle velocity and collisions

M1c, M4a, M5b

WS1.1b, WS1.2a, WS1.2e, WS1.3e, WS1.4a

Demonstration of the behaviour of marshmallows in a vacuum.

P1.3e ☑ explain how doing work on a gas can increase its temperature

examples such as a bicycle pump

WS1.1b, WS1.2a

Demonstration of heat production in a bicycle inner tube as it is pumped up.

P1.3f ☑ describe a simple model of the Earth’s atmosphere and of atmospheric pressure

an assumption of uniform density; knowledge of layers is not expected

M5b

P1.3g ☑ explain why atmospheric pressure varies with height above the surface of the planet

P1.3h ☑ describe the factors which influence floating and sinking

P1.3i ☑ explain why pressure in a liquid varies with depth and density and how this leads to an upwards force on a partially submerged object

WS1.1b, WS1.2a, WS1.3a, WS2a

Discussion of buoyancy of a ping pong ball in water.

P1.3j ☑ calculate the differences in pressure at different depths in a liquid

knowledge that g is the strength of the gravitational field and has a value of 10 N/kg near the Earth’s surface

M1c, M3c

WS1.1b, WS1.2a

Demonstration of differences in water pressure using a pressure can with holes.

Pressure

Next Steps

Learning Objectives