How Thrust and Pressure Differ: Key Principles & Applications
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,
Fb = vpg. Fb = 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.
FAQs on Thrust Pressure Explained: Meaning, Formula & Examples
1. What is the fundamental difference between thrust and pressure?
The fundamental difference lies in what they measure. Thrust is the total force exerted by an object perpendicular to a surface. It is simply a type of force, measured in Newtons (N). Pressure, on the other hand, is the effect of that thrust distributed over a specific area. It is defined as the thrust per unit area and is measured in Pascals (Pa) or N/m².
2. How is pressure calculated using thrust and what is its formula?
Pressure is calculated by dividing the total thrust (perpendicular force) by the area over which the thrust is applied. The formula is:
Pressure (P) = Thrust (F) / Area (A)
This formula shows that for the same amount of thrust, pressure is inversely proportional to the area. A smaller area results in higher pressure, and a larger area results in lower pressure.
3. Why does a sharp knife cut vegetables more easily than a blunt one?
This is a classic example of the relationship between force, area, and pressure. A sharp knife has a very small surface area along its cutting edge. When you apply a force (thrust) with the knife, this force is concentrated over that tiny area, creating extremely high pressure. This high pressure is sufficient to slice through the vegetable. A blunt knife has a larger edge area, so the same amount of force results in much lower pressure, which is not enough to cut easily.
4. What are some common examples of thrust in action?
Thrust is the perpendicular force acting on a surface. Some common examples include:
The force a person exerts on the ground while standing, which is equal to their weight.
The forward push generated by a rocket engine expelling hot gases downwards.
The force a nail exerts on a wall when you hammer it.
The upward buoyant force, or upthrust, that water exerts on a floating boat.
5. Can you provide some real-world examples of pressure?
Pressure is observed all around us. Key examples include:
A thumbtack has a sharp point to maximise pressure and a flat head to minimise pressure on the thumb.
Tractor and army tank wheels are fitted with broad chain belts to increase the surface area, which reduces the pressure on the ground and prevents them from sinking.
The straps of a heavy school bag are made wide to distribute the weight over a larger area, reducing the pressure on the shoulders.
Atmospheric pressure is the pressure exerted by the weight of the air in the atmosphere.
6. If thrust is just a force, why do we need a separate term for it?
While thrust is a type of force, the term is used specifically to denote the component of force that acts perpendicular (at 90 degrees) to a surface. This distinction is crucial for understanding concepts like pressure, which depends entirely on this perpendicular force. A force applied at an angle to a surface has two components, but only the perpendicular one contributes to pressure. Using the term 'thrust' provides this specific and important context.
7. How do the principles of thrust apply to rockets and jet engines?
In rockets and jet engines, thrust is generated based on Newton's Third Law of Motion (for every action, there is an equal and opposite reaction). The engine forcefully expels hot gases (mass) backwards at high velocity. This action of pushing the gas out creates an equal and opposite reaction force that pushes the rocket or jet forward. This forward-pushing reaction force is the thrust that overcomes drag and accelerates the vehicle.
8. What is fluid pressure and how does it act on a submerged object?
Fluid pressure is the pressure exerted by a fluid (a liquid or a gas) at a certain depth. Unlike a solid that exerts pressure only downwards, a fluid exerts pressure in all directions. When an object is submerged in a fluid, the fluid exerts pressure on all parts of the object's surface. This pressure increases with depth. The pressure on the bottom of the object is greater than the pressure on the top, resulting in a net upward force called buoyant force or upthrust.
