How does a hydraulic system work? Starter: List the main properties of liquids and gases. What are the main similarities/differences between them ?

Glossary words Pressure – force per unit area acting on surface at right angles to the surface. Unit is pascals (Pa) Hydraulic pressure- the pressure in the liquid in a hydraulic arm.

Which is the best shoe for the job and why? Walking on snow Gripping better on mud Ice skating Sinking into the mud D b A C

Why do you not get spiked to death on this ?

Pressure recap Pressure is force per unit area …. Pressure (Pa) = Force/ area Have a go at these questions. Force 50N on a stiletto of 5 m2 Force of 100N on a shoe of 0.3m2 Pressure is 70 Pa, force is 20N what is the area?

Demo Why do the leaks in the bottle all travel the same distance? Observe: pressure increases with depth.

Hydraulic Machines Force MULTIPLIERS How much effort would you have to put into stop a car like this ….

Instead we use a force multiplier

Demo: syringes

Hydraulics Pressure is the same throughout liquids and is virtually incompressible. (volume wont change with pressure). A force exerted on a liquid is transmitted through the liquid. Even better….. The force can be multiplied by increasing the area where the force acts!

Uses of hydraulics

Check point Hydraulic systems are called Force Multipliers. Why?

Lifting a big weight with a small force…

Lifting a big weight with a small force… Force 1 (F1) = effort Force 2 (F2) = Load Area 1 (A1) = 10 cm2 Area 2 (A2) = 30 cm2 1) Work out the pressure on the effort. 2) Work out the pressure on the load. P = F/A P = 50/10 = 5Pa P = F/A 5 = F/30 5X30 = F F = 150N

Working out the pressure Force1 F1 is applied is called the effort. The force exerted F2 is the load. The load is moved by a smaller effort. P = F1 where A1 is the piston area. A1 The pressure acting on the wider piston = PA2 In other words – F2 = F1 X A2 http://science.howstuffworks.com/transport/engines-equipment/hydraulic1.htm

Have a go at the questions