Page 155 - Physics

Pressure

Applications of the hydraulic press There are identical systems on
1. A hydraulic press can be used in industries all four wheels ensuring the
to compress bulky items. The purpose is to same braking force on each
compress a large object such as a bale of wheel so that the vehicle slows
cotton into a small size for more economical down uniformly. When the
transport, as shown in Figure 7.20. pressure on the brake pedal is
removed, the return spring pulls
Bale of
Compression cotton F 2 the brake shoes away from the
F 1 chamber drum and the wheels become

A Piston 2 free to rotate.
Piston 1 2 pushed 3. It is used in industries in the
pushed A 1 up
down forming of metals.
4. Since the hydraulic press acts
like a lift, it is used for lifting
Figure 7.20: Compressing bale of cotton heavy loads. The pressure
applied on the small piston
As the small piston is pushed down, the large creates a large force on the
piston is pushed upwards compressing the large piston which lifts the
bale of cotton. The amount by which the
force applied to piston 1 is increased depends load. Figure 7.22 shows a crane
on the ratio of the areas of the two pistons. lifting a heavy load.
2. Another application of the hydraulic
press is in hydraulic brakes, as shown
in Figure 7.21.
Brake pedal
Master cylinder

Slave cylinder

Brake drum

Brake shoe

Figure 7.21: Hydraulic brake system Figure 7.22: A crane lifting a heavy load

When pressure is applied to the brake pedal, Measuring pressure using a
it pushes the piston in the master cylinder manometre
forward creating pressure in the brake fl uid.
This pressure is transferred to the slave A manometre is a simple device used
cylinders where the force is multiplied and to measure pressure (commonly gas
pushes the brake shoes against the brake pressure). It uses the property that
drum that is attached to the wheel of the the pressure due to the weight of a
vehicle. Friction between the brake shoes and fl uid of constant density is given by
the drum slows down the wheels’ rotation. P = hρg.

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Physics Form 1 Final.indd 149 16/10/2024 20:57