1. Hydraulics
Noadswood Science, 2013

2. Hydraulics
Friday, February 22, 2019
To explain how hydraulics work

3. States Of Matter
Remember, there are 3 states of matter – solids, liquids, and gases (only gases can be compressed (squashed))
In liquids and gases the particles are moving around – as they bump into the surface the force of the particles hitting it causes pressure
Solids
Liquids
Gases

4. Pressure In Gases
Pressure is caused by the force of particles hitting the side of the container
Why does tyre pressure increase when you pump more air into it?
Particles in gases are normally spaced far apart
When a tyre is pumped up, the air gets compressed (squashed) inside – this means there are more gas particles trapped inside
As there are more particles inside the tyre, particles hit the sides of the wall more often, increasing its pressure

5. Pressure Outside?!

6. Pressure In Gases: Boyle’s Law
Squashing a gas into a smaller space causes the pressure to increase in proportion to how much you squash it
Squash the gas into ½ the space, and it will result in 2x the pressure
Squash the gas into ¼ the space, and it will result in 4x the pressure
Boyle’s Law - there must be a fixed amount of gas (i.e. none escapes) and there must remain a constant temperature
¼ the space, and the particles will hit the wall 4x as often (pressure quadruples)
½ the space, and the particles will hit the wall 2x as often (pressure doubles)
Gas particles randomly hit the side wall

7. Pressure In Liquids Pressure in a liquid acts in all directions
Pressure in a liquid increases with depth – can you explain why?
Low pressure
High pressure

8. Pressure In Liquids
The greater the depth, the greater the pressure (the weight of the water above compresses the water below)
Low pressure
Pressure = gravity (10N/kg) x depth (m) x density (kg/m3)
Pull of gravity (on Earth)
Greater the depth, the greater the pressure
The denser the liquid, the heavier it is
High pressure

9. Pressure In Liquids
Liquids (like solids) are virtually incompressible (squashed) as there are no gaps between the particles
As liquids cannot be compressed, they can be used to send forces from one area to another – these are known as hydraulic systems

10. Pressure Pressure is exerted when a force is applied over an area
Pressure is measured in Newtons per square meter (N/m2) also known as Pascals (Pa) – it can also be measured in N/cm2
With a big enough area, you can stay on top of the powder…
1N/m2 = 1Pa

11. Pressure To work out pressure you need to know two things: -
The force (or weight) applied
The area over which the force (or weight) acts upon
Force
(F)
Pressure
(P)
Area
(A)
Pressure = Force  Area Area = Force  Pressure Force = Pressure x Area

12. Hydraulics F P A
How can you stop a car at 70mph using just your foot? How about stopping a motorbike at this speed with two fingers?!
Pressure is transmitted equally in all directions through a liquid
Hydraulic systems can be used to increase the size of a force (master piston applies the force which is transmitted to the slave piston)
Force of 10N
Master Piston
10cm2
Slave Piston
20cm2
Pressure at master = 10N ÷ 10cm2
Pressure = 1N/cm2
Force on slave= 1N/cm2 x 20cm2
Force = 20N

13. Nothing Free
The slave piston has a larger area than the master piston, so the force exerted by the slave piston on the brakes is greater than the force exerted at the master (i.e. you get much more force from slave when you gently press the master)
This is how you can stop a very heavy object, traveling at high speed, by simply using your foot / your fingers
The larger force at the slave piston comes at a price – it only moves the slave piston half the distance (so the energy out is the same as the energy in)

14. Pressure
Complete the pressure worksheet

15. Pressure Pressure = Force ÷ Area Force = Pressure x Area
Pressure = 20N
Force = 20 x 25
Force = 500N
So a force of 100N to the master gives a force 5x bigger of 500N to the slave