• SLC Science
  • Gravitational force
    • Law of gravitation
    • Acceleration(g)
    • Free fall
    • Numerical Problems
  • Pressure
    • Def.Pressure
    • Principles
    • Upthrust
    • Numerical Problems
  • Heat
    • Heat Energy
    • Anomalous expansion of water
    • Specific heat capacity
    • Numerical Problems
  • Electricity
    • Electricity
    • Fuse
    • Faraday'sPrinciple
    • Transformer
    • Numerical Problems
• SLC English
• SLC Mathematics
• SLC Opt.Maths
• +2 Science
  • Wave Motion

Pressure

Definition: The force exerted on per unit area perpendicularly is called pressure.
It is denoted by P. And its unit is N / m² or Pascal (pa).
By the formula Pressure P = $\frac{F}{A}$

Pressure depend on
• Directly on applied force (F)
  
• Inversly on the sureface area (A).
  

Q. Write the relationship between force, surface area and pressure exerted?
Q. Prove that:- Pressure P, Force F and Area A then P = $\frac{F}{A}$

→ Pressure exerted is directly proportional to applied force i.e. P ∝ F Pressure exerted on surface is inversly proportional to surface area i.e. P ∝ $\frac{1}{A}$ Combining these these two we have P ∝ $\frac{F}{A}$ or, P = k. $\frac{F}{A}$, where k is constant For F = 1 N, A = 1 m2. We have P = 1 pa. Therefor k should be 1. Hence we get, P = $\frac{F}{A}$ Hence proved.

Q. Define 1 Pa pressure?
→ The pressure exerted by 1N force on the 1 m² is called 1 pascal pressure.

Difference between Force and Pressure
Force	Pressure
1. The external agent which bring change is state of object.	1. It is the perpendicular force perunit area.
2. Its Unit is Newton (N).	2. Its Unit is Pascal (Pa)
3. Force F = m.a.	3. Pressure P =$\frac{F}{A}$

In our daily life somewhere we have to increase pressure and somewhere to decrease.
• To cut vegetable we have to increase pressure so that the knife is made sharp (decrease area to increase pressure).
• To increase pressure on ground football shoes are studed that's why player don't slips and become easy to run.
• While walking on graveled road with bare foot less surface of stones touch to feet sothat greater pressure occure on feet which made difficult to walk.
• Rare wheels of tractor are made large and wide so that there is low pressure on groud and become easire to move.
• To minimise pressure on ground heavy vehicle's tyres are made double wheeled and become easir to move.
• Due to high pressure on pressurecoocer, rice prepared faster than open vessel.

Do Yourself.
• Q. Studs are made on the sole of the football player's boot?
• Q. It is difficult to walk on bare feet in a graveled road?
• Q. The rear wheels of a tractor are made larger and flat?
• Q. The tyres of heavy vehicles are made double-wheeled?
• Q. Sharp knife cuts vegetable more easily than a blunt one. Give reason.
• Q. Two rectangular water tanks, one (A) having a larger base area than the other (B), carry equal volume of water. Explain whose bottom experience more pressure?
• Q. One of the two ladies with same weight is wearing pointed heeled shoes and other wearing flat shoes. Explain which one exerts more pressure on the ground.

Liquid Pressure Pressure exerted by liquid P = h d g where h is depth of liquid, d is density and g is acceleraion due to gravity. Pressure exerted by the liquid directly depends on depth 'h' density 'd' gravitational acceleration 'g'. → As the depth of liquid increase pressure exerted by it also increases and vice versa. → As the density of liquid increases pressure increase and vice versa. → As the gravitational acceleration 'g' increases pressure increase and vice versa.

Q. Prove that: Liquid pressure P = h d g?
→

Suppose vessel of base area 'A' and height 'h' filled with liquid of density 'd' then volume liquid V = A.h Mass of liquid m = d.V = d.A.h (since, d = $\frac{M}{V}$) Weight of liquid W = m g = d.A.h.g Pressure P = $\frac{W}{A}$ P = $\frac{\mathrm{d.A.h.g}}{A}$ P = h.d.g. Hence proved

• To resists higher pressure at higher depth Dam are made wider base.
• The tap at lower floor is more depth than upper floor tap. Therefor lower floor tap experience high pressure so speed of water flow is more at lower floor tap than that of upper floor tap.
• A hole at bottom of boat is at higher depth than hole at side. Therefore hole at bottom is higher pressure which cause more dangerous then hole at side.
• At higher point (top of hill) gravitational acceleration is low. Therefor pressure at the bottom of a drum filled with water goes on decrease if it is brought to Himalaya from Terai.
• Depth of blood on feet is higher on feet than head so blood pressure on feet is higher than head.
• Due to low pressure near to the surface of water, air buble expanded as come to near the surface of water.
• To resist high pressure, person who goes to bottom of sea wear strong diving suits.

Do Yourself.
• Q. Name the factors on which pressure depends. Also, show their relation with the pressure being exerted.
• Q. The water supply tanks are placed higher than any other building in a town. Explain the reason.
• Q. Deep sea divers wear special diving suits. Explain the reason.

Density
Definition: Mass of substance perunit volume is called its density.
It is denoted by D. And its unit is Kg / m³ or gm / cm³.
By the formula, Density D = $\frac{M}{V}$ $$

Definition of Relative density: Is the ratio of mass of substance of fixed volume to the mass of water of 4 ⁰ C of equal volume.
By the Formula Relative density = $\frac{\mathrm{mass\; of\; substance\; of\; certain\; volume}}{\mathrm{mass\; of\; water\; of\; 4\; ⁰\; C\; of\; same\; volume}}$
It is relative measure so its no unit.