Hydraulic lift

Hydraulic lift


Hydraulic lift . This is commonly used in garages; it lifts cars so that repairs and service on them can be done easily underneath the car.
A force applied to the small piston, raises the large piston, which lifts the car. One valve allows the liquid to pass from
The small cylinder to the wider one, a second valve allows more liquid (usually oil) to pass from oil reservoir on the left
to the small cylinder. When one valve is open, the other must be shut.

(b) Hydraulic brake:

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When the brake pedal is placed, the pressure exerted inside the master cylinder is transmitted equally to all the slave cylinders.

At the slave cylinder, the pressure acts on the pistons which are connected to the brake shoes (pads).
This presses the brake shoes against the brake drum (disc) hence creating friction, which opposes the rotation drum and therefore the wheel. This results in the stopping of the car.

Factors affecting pressure in fluids

Generally, pressure at any point in a liquid is the same in all direction and depends on the following factors:
i) Depth “h” below the surface of the liquid
ii) Density 𝛒 of the liquid
iii) Pressure exerted on the surface of the liquid.

Experiment to show that pressure increases with depth.

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Equally, spaced holes A, B and C of the same size are drilled at different depths along one vertical side of a cylindrical can.
The holes are then closed using corks.
Water is then poured into the can to full capacity.
The corks are then removed at the same time and the distance from the can to where water fom each hole lands noted.

Water comes out fastest and lands furthest from the lowest hole C followed by B and then least from A.
This means that pressure is highest at C, which is deepest. Hence, pressure in liquids increases with depth.

Water supply system:
Water supply often comes from reservoirs at a higher ground level. In a very tall building, it is necessary to pump water to a large tank in the roof.
All the above are done because the lower the place supplied the greater the water pressure at it.

Experiment to show that pressure depends on density

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Two tall jars of the same size and height, each with a hole punched at equal depth are used.

The jars are then filled to the same height, with liquids of different densities e.g paraffin and water.
The distance to which the liquids jet out is observed and compared.
It is observed that water jets furthest compared to paraffin i.e; x2>x1.Thus the higher pressure is exerted by water than paraffin at the same depth.
Therefore, the higher the density, the higher the pressure.