Pressure

Question 1

explain how gas particles in a box exert a pressure on the box

Answer 1

• particles in constant random motion
• when they collide with the walls of a box there is a change in momentum
• therefore, due to newton’s second law, there is a force exerted on the particle
• newton’s third law means that force exerted on the particle by the box is equal and opposite to the force exerted on the box by the gas particles
• sum of all forces / area = pressure

Question 2

a crisp packet is sealed at sea level, explain what would happen if it was taken up on a plane

Answer 2

• pressure inside is fixed
• external pressure drops as air is less dense
• therefore less particles, so less frequent collisions outside the crisp packet
• force from gas inside is constant but force from outside is lower
• crisp packet will swell