Starter: Without looking in your book can you remember the formula for finding… Density Pressure Pressure in liquids

Starter: Without looking in your book can you remember the formula for finding… Density Pressure Pressure in liquids 𝐷𝑒𝑛𝑠𝑖𝑡𝑦 ρ= 𝑚𝑎𝑠𝑠 𝑚 𝑣𝑜𝑙𝑢𝑚𝑒 𝑣 = 𝑘𝑔 𝑚 3 𝑃𝑟𝑒𝑠𝑠𝑢𝑟𝑒 𝑃= 𝐹𝑜𝑟𝑐𝑒 𝐹 𝐴𝑟𝑒𝑎 𝐴 = 𝑁 𝑚 2 =𝑃𝑎 𝑃𝑟𝑒𝑠𝑠𝑢𝑟𝑒 𝑃= ρ𝑔ℎ= 𝑁 𝑚 2 =𝑃𝑎

Homework Using hydraulic systems worksheet Answer all questions showing all working clearly & drawing out a diagram (not complicated) for each question. Due in next Monday.

Lesson goals… To explain why pressure and forces are transmitted through liquids and gases. To explain the principles behind hydraulic lifts/ brakes. To explain and use a manometer to measure gas pressure.

Hydraulic machines If you push on the top syringe plunger what will happen? Would there be a difference if the syringe system was filled with air not water?

Hydraulics Pressure is transmitted through a fluid. A hydraulic machine uses this to multiply a force e.g. car brakes. A hydraulic system will not work if any air is trapped within it. The air will not transmit pressure, but will be compressed. The particles in the liquid are much closer together and so can not be compressed.

Force = Pressure x Area A small force F1 on a small area A1 transmits a pressure through the liquid which over a larger area A2 creates a much larger force F2 The pressure at the small piston = pressure at the large piston. F2

Y X 9

Piston X puts pressure on the liquid Force = 20N Force = 10N Piston X puts pressure on the liquid Y X Area = 10cm2 Area = 40cm2 How do we calculate the pressure that is being applied from piston X? 10

f p a force area Force = 20N Force = 10N Y Area = 10cm2 pressure = X Ask pupils to calculate the pressure from piston x. Demonstrate how to calculate the force by rearranging the equation (higher pupils will probably only understand this point) Area = 10cm2 pressure = force Area = 40cm2 area 11

What would the pressure be at piston Y? Force = 20N Force = 10N The pressure stays the same throughout the liquid Y X The same as piston X = 1N/cm2 Area = 10cm2 Area = 40cm2 What would the pressure be at piston Y? 12

Hydraulic brake hydraulic fluid slave pistons foot pedal master piston All hydraulic brake systems (e.g. in a car) use a small master piston and a bigger slave piston. hydraulic fluid slave pistons foot pedal master piston The master piston is used to apply a force. This puts the liquid under pressure. The pressure is transmitted to the pistons on all four wheels of the car.

Hydraulic Brake

Hydraulic Example Stick example into your book and complete.

Manometer A manometer uses the fact that liquids transmit pressure to measure the pressure of a gas. The difference in pressure of the gas to atmospheric pressure is found using the difference in height h. ΔP = ρgh

Using a manometer Use the manometer to measure the pressure of the gas supply. Turn on the gas supply GENTLY! Measure the difference in height between the two halves of the manometer. In your books. Draw a diagram of the manometer & explain how it measures gas pressure. What were your results?