[Physics Class Notes] on Thrust Pressure Pdf for Exam

Did you enjoy floating around in swimming pools when you were young? Have you observed how delighted a child is when he sees his little toys floating in the water? He plays so many games with them! Have you found yourself wondering how objects float in water? What is this phenomenon all about? This is not, there’s most! Let’s unravel the secret of thrust and pressure which makes so much in this world possible. 

Thrust Pressure 

The pressure that is applied on a wooden block in a direction perpendicular to it, is known as Thrust. When a continuous force is applied to an object against the body that it is in contact with, it is known as pressure. If we have to understand the difference clearly, then thrust is the force being exerted on the object while pressure is the force acting on the object per unit area. 

Hence Thrust is measured by the unit “N” and pressure is denoted by the unit “Nm raised to the power of -2.” 

Fluid Thrust

One day, a boy was playing with his cricket ball that suddenly fell into the bucket of water. A boy asked his mother why this ball stays at the surface of the water instead of sinking to the bottom? His mother replied it’s because the pressure exerted on the ball keeps the ball on the plane surface.

So, fluid thrust and pressure is the phenomenon that keeps the ball on the plane surface. This can also be called a hydrostatic thrust on a plane surface of the object in the fluid.

This type of situation comes when the upthrust force or the thrust becomes equal to the weight of the ball. So, the total normal force exerted by the liquid on the object is called the fluid thrust.

What is the Magnitude of Fluid Thrust?

Solids exert pressure on liquids due to their sheer weight. An upthrust is equal to the weight of the liquid that gets displaced by an object. Thus Upthrust = volume of the body sinking in the fluid x density of the fluid x acceleration due to gravity. 

Where,

F_b = vpg. F_b = upthrust

v= volume of the body sunk in the fluid

p = density of the fluid

g = acceleration due to gravity 

Similarly, a fluid also exerts pressure on the walls of the container it is enclosed in. This fluid pressure is directly proportional to the depth and density of the fluid and it depends on g, which is the acceleration due to gravity. However, at certain places, its value remains constant. 

P (Fluid Pressure) = h (height of vertical column) x d (density of fluid) x g (acceleration due to gravity)

Examples on Thrust

• School bags have larger straps so that the pressure exerted on shoulders is less.

• Cutting nails is an example of thrust.

• Sucking a cold drink through a straw.

• Breathing

• If we look at an example of thrust and that is building construction.

• Pushing an empty vessel into the water, it experiences the buoyant force.

• Pushing a cork into the water, it experiences the buoyant force.
  

Examples on Pressure

• The best example for the thrust is Knives.

• We see that the edge of the knife is very small, which means the force exerted by it is very large and this force on the area is termed pressure.

• Doctors use a syringe to take blood for blood tests. The pressure of the blood forces the liquid (blood) to move into the syringe when its plunger is withdrawn.

• When air is seized out of a drinking straw, the air pressure inside it reduces, and the atmospheric pressure outside forces the liquid (a drink) to go inside the straw.

• Skis have a huge area to decrease the pressure on the snow, which assures that the skis do not sink into the snow too far.

• The pressure in the studs on the soles of sports shoes of footballers are high enough for them to sink into the ground, which gives extra grip.

• A vaccum cleaner device has a fan fixed inside it which creates a low pressure inside it. Consequently, air and dirt particles are captured by force into the device.
  

Applications of Thrust and Pressure

• Let’s say, you cut an apple with a knife, and if you observe one thing the area of an apple is large, which makes the cutting easier.

• The soles of football shoes have spikes that allow the easy movement of players on wet mud. These spikes reduce the area of contact and increase the pressure on the track. This provides a better grip on the ground.
  

Summary

The force applied to the object is called the thrust and when the liquid applies thrust to an object and makes it flow over it, such kind of thrust is the fluid thrust.