# Thrust Pressure

View Notes

Thrust is the pressure exerted on the surface of the wooden block in a direction perpendicular to it, while pressure is a continuous force that is applied to the object against a body in contact with it.

The SI unit of thrust and pressure is N and Nm$^{-2}$, respectively.

So, thrust is a force exerting on the object and the pressure is the force acting on the object per unit area. The formula for the pressure exerted is Force upon the area.

[Image will be Uploaded Soon]

### Fluid Thrust and Pressure

Generally, in fluids, the pressure is always perpendicular to the surface of an object.

The pressure applied to an object makes the object submerged in water, the type of force applied is the thrust force. The pressure applied by the fluid is the pressure that produces a thrust on the object and this is the reason some objects float in water.

[Image will be Uploaded Soon]

### Fluid Thrust and Pressure Example

We know that the upward force exerted on a body by the fluid in which the body is submerged is known as the upthrust/buoyant force. The property of liquid to exert an upward force on the body dipped in it is called buoyancy

In the system of international units or SI, the unit for measuring a force upthrust is Newton or kgf.

### Thrust Pressure

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 exerting 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.

### Magnitude of The Fluid Thrust

Upthrust equals the weight of the liquid displaced by the object

Upthrust  =  volume of the body sinking in the fluid × Density of the fluid × Acceleration due to gravity

FB = vρg, Where FB is the Upthrust

v =  Volume of the body submerged/sunk in the fluid

ρ = Density of the fluid in which the body is dipped

g = Acceleration due to gravity

The thrust and pressure have many real-life applications:

### Examples of Thrust and Pressure in Our Daily Life

Let’s consider some of the daily life examples to understand the thrust and pressure in the simplest way:

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 cooldrink 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 vacuum 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 that 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.

FAQ (Frequently Asked Questions)

Question 1: Describe the Relationship Between the Thrust and the Pressure.

Answer: We know that the pressure is the thrust per unit surface, which plays an important role in every real-life situation.

When the luggage is heavy, the force acting per unit area decreases with broad straps of the handles. Hence lesser pressure eases a person holding this luggage.

Similarly, the lesser surface area of the nails or simply the pointed tips shift a larger force exerted on them and helps the easy fixing of them in walls. As pressure is force per unit area, its units are newton per meter square.

Here, one meter per meter square is termed Pascal (Pa) after the scientist named Blaise Pascal. The pressure exerted by solids relies more on their weight and surface area through which the weight acts.

Question 2: What is the Thrust in a Rocket Engine and a Jet?

Answer: Thrust is a reaction force that can be expressed quantitatively by Newton's third law. When a body or a system expels or accelerates mass in one direction, the accelerated mass will cause a force of equal magnitude but in the direction opposite to one that is applied to that system.

The force that causes an object to move ahead is the thrust.

Thrust in a jet or rocket engine develops as a result of the reaction to the ejection of exhaust gases from the rear of the engine. Thrust in a propeller occurs due to the spinning of the propeller blades that pushes air or water in a certain direction.