Transcript Topic 4: Pressure

Topic 4: Pressure
Pressure = Force÷Area
• p = F/A
• The unit for pressure is the pascal, which
is written as Pa.
• 1 Pascal = 1 Newton/1 square meter
• Pa = N/m2
• Eg. A woman has a weight of 600 N, and the soles of her
feet have a combined area of 0.5 m2, what is the
pressure on her feet?
• p = F/A = 600N/0.5m2 = 1200 Pa.
Pascal’s Law
• In a closed system, where the fluid cannot
escape, any pressure that is placed on the
fluid will be transmitted equally in all
directions.
• Pascal’s law is used in hydraulic systems
like car lifts.
• Hydraulic systems involve a large
mechanical advantage.
Hydraulic Systems
• Hydraulic systems involve a small cylinder
which pressurizes the liquid. Pascal’s law
says that the pressure will travel,
undiminished, throughout the liquid.
• In a hydraulic system the pressure will
cause the cylinder at the other end to raise
up.
Pascal’s Law and Hydraulics
• According to Pascal’s law, the pressure is
the same on both ends, therefore the force
at the larger cylinder (larger area) will be
larger than the effort force going onto the
smaller cylinder.
• pressurein = pressureout→Fin/Ain = Fout/Aout
Example
• A mechanic exerts a force of 200 N on a
0.5 m2 piston cylinder. At the other the
large, 10 m2 cylinder moves up. What is
the most force that it can exert upward?
• pinput = Finput/Ainput = 200 N/0.5 m2 = 400 Pa
• pinput = poutput = 400 Pa
• Foutput = 400 Pa X 10 m2 = 4000 N