Hydraulics How does a hydraulic system work Starter

Hydraulics 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? Ice skating Walking on snow Gripping better on mud 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. 1) Force 50 N on a stiletto of 5 m 2 2) Force of 100 N on a shoe of 0. 3 m 2 3) Pressure is 70 Pa, force is 20 N 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 (F 1) = effort Area 1 (A 1) = 10 cm 2 1) Work out the pressure on the effort. P = F/A P = 50/10 = 5 Pa Force 2 (F 2) = Load Area 2 (A 2) = 30 cm 2 2) Work out the pressure on the load. P = F/A 5 = F/30 5 X 30 = F F = 150 N

Working out the pressure • Force 1 F 1 is applied is called the effort. • The force exerted F 2 is the load. • The load is moved by a smaller effort. P = F 1 A 1 where A 1 is the piston area. The pressure acting on the wider piston = PA 2 In other words – F 2 = F 1 X A 2 A 1 http: //science. h owstuffworks. c om/transport/e nginesequipment/hyd raulic 1. htm

Have a go at the questions