Overview of Force and Pressure
Before going through force and pressure in detail. Let us first have an overview of it. Force is applied in order to perform a work. If we talk about pressure then pressure is the force that is applied per unit area. Force is applied perpendicular to the surface per unit area. The unit of measurement of pressure is pascal. A Pascal is basically defined as the pressure exerted by one force of Newton on one square unit area.
Where there are similarities between the force and pressure but in actual force is the total effect of one object on the other one whereas If we talk about pressure it us the certain amount of force that is applied on a unit area. That is you can define pressure in the physical quantity of the force that is spread over a unit area. Since we know that force is directly proportional to pressure, in this context if the force applied on an object it will be increased in the same way pressure will also increase. You can go through this article as this article will provide you a brief knowledge of pressure and force. In this article you are going to study about force and pressure, properties of Force, type if force, thrust and pressure and further you will be provided with the Frequently Asked questions related to the force and pressure topic that will increase your knowledge and will help you to get a clear insight of this topic pressure and force.
Force and Pressure Definition
A kind of push or pull is known as force. It is something whose action generates motion in an object. or, it can also be defined as the interaction between two objects. Force has a magnitude as well as direction. Magnitude is used to express the strength of the force. A change in direction or magnitude or both also changes the force. Exerted force on an object may change the speed with which the object moves, the direction of motion or shape. When we measure the amount of force acting on a unit area, it is called pressure.
We will study more about force, it’s types, physical properties and pressure in this article.
Properties of Force
The force exerted away from the body is a push. And a pull is a force exerted towards the body. Thus, a force is a push or a pull.
When the force is being applied in the direction of motion of the object then it mostly increases its speed and when it’s applied in the opposite direction, the speed decreases.
Thus, the state of motion of an object is explained by its speed and the direction of motion.When the speed is zero, the body is considered to be at a state of rest.
An object cannot move, change its direction or speed by itself. Which implies that an external force acting upon the body can change its speed, motion, direction, and shape.
The resultant of all the forces acting on a body is known as the net force. And, the acceleration of the body is along the direction of the net force.
The force that opposes the relative motion between two surfaces is called frictional force.
Frictional force acts between the surface of the two bodies in contact with each other.
Types of Force
Force is applied to a body in order to perform a work. There are numerous forces that can be applied that for every force there are a number of varieties or types. Let's have a look at these forces.
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Frictional Force - The force that opposes the relative motion between two surfaces is called frictional force. The frictional force acts between the surface of the two bodies in contact with each other
Muscular Force - When force is caused or carried out by the action of muscles is called muscular force.
Magnetic Force - Force acting between two magnetic bodies as a result of their poles is called magnetic force. Magnetic Force is usually an attracting force.
Gravitational Force - Earth exerts a pull on all objects or bodies towards itself. This pull is known as gravitational force. As a result of gravitational force, every object in this universe, irrespective of its size and shape, exerts some force on every other object.
Electrostatic Force - Electrostatic Force, also known as the Coulomb Interaction is basically a force applied by a charged body on another charged or uncharged body called electrostatic force. In other words, the electrostatic force is an attractive or repulsive force acting between two electrically charged objects.
Buoyant Force - It is an upthrust force exerted by fluid opposing the weight of the object that is fully or partially immersed in that fluid. Buoyancy is generally caused by the differences in pressure acting on opposite sides of an object immersed in a static fluid.
Tension Force - Tension force acts when a rope or string or any similar object is pulled by forces acting from the opposite direction. It is directed over the length of the wire or the string.
Drag Force - Drag force also acts in a fluid like water or air. It is the resistant force caused by the motion of a body through a fluid. Drag force is the one that acts opposite to the direction of the oncoming flow velocity.
Spring Force - It is a type of restoring force. This is because the force exerted by the spring is always in the opposite direction to the displacement.
Nuclear Force - It is a force that acts between all the particles in the nucleus. That is the force acting between two neutrons, between two protons and between a neutron and a proton. A nuclear force is always an attractive force.
Thrust and Pressure
Force acting on a unit area is known as pressure. The SI unit of pressure is Pascal and it is given by P= Force/Area. Thus, it can be seen that pressure is the ratio of the force to the area over which the force is acting.
Pressure (p) =\[ \frac{\text{Force (Fn)}} {\text{Area (A)} }\]
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Thrust, on the other hand, is a reaction force. When a system accelerates a body with a mass in one direction, the acceleration causes a force of equal magnitude in the opposite direction upon the system. The force applied in a perpendicular direction on the surface is called thrust.
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Thrust is measure in Newtons and can be calculated by the formula-
Thrust = Pressure × Area
Some objects that float in water are because of thrust. Also, objects weigh less in water because of the same phenomenon.
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Now before moving to another topic let's have a look at the Frequently Asked questions related to force and pressure.
FAQs on Force and Pressure
1. What is a force and what causes it to act?
A force is simply a push or a pull on an object. According to the NCERT syllabus for Class 8, a force arises due to the interaction between at least two objects. For example, to move a book, you must interact with it by pushing or pulling it. An object cannot experience a force without interacting with another object.
2. What are the different effects a force can have on an object?
A force can produce several effects on an object. As per the CBSE Class 8 curriculum for 2025-26, these include:
- It can make a stationary object move.
- It can stop a moving object.
- It can change the speed of a moving object (make it faster or slower).
- It can change the direction of a moving object.
- It can change the shape or size of an object (e.g., squeezing a sponge).
3. What is the difference between contact and non-contact forces? Provide examples.
The main difference lies in whether the objects need to be touching for the force to act.
- Contact Forces: These forces act only when objects are in direct physical contact. Examples include muscular force (lifting a bag) and frictional force (a ball slowing down on the ground).
- Non-Contact Forces: These forces can act from a distance without any physical contact between the objects. Examples include magnetic force (a magnet attracting an iron pin), electrostatic force (a charged comb attracting paper bits), and gravitational force (an apple falling from a tree).
4. What is pressure, and how is it related to force?
Pressure is defined as the force acting perpendicularly on a unit area of a surface. The relationship is given by the formula: Pressure = Force / Area. This means pressure is directly proportional to the force applied and inversely proportional to the area over which the force is distributed. If you apply the same force over a smaller area, the pressure will be higher.
5. Why do school bags have wide straps instead of thin ones?
This is a practical application of the concept of pressure. School bags have wide straps to increase the surface area over which the weight (force) of the bag acts on the shoulders. According to the formula Pressure = Force / Area, increasing the area reduces the pressure exerted on the shoulders. This makes the bag more comfortable to carry and prevents the straps from digging into the skin, which would happen with thin, high-pressure straps.
6. Why is it much easier to cut an apple with a sharp knife than a blunt one?
It is easier to cut with a sharp knife because it creates higher pressure. A sharp knife has a very thin edge, meaning its contact area is extremely small. When you apply a force, this small area concentrates the force, creating very high pressure that easily slices the apple. A blunt knife has a larger area, so the same force results in much lower pressure, which is often insufficient to cut through.
7. What is atmospheric pressure and why don't we feel it crushing us?
Atmospheric pressure is the pressure exerted by the weight of the air in the atmosphere all around us. We don't feel this immense pressure because the pressure inside our bodies (from our blood and other fluids) is approximately equal to the external atmospheric pressure. These forces balance each other out, so we are not crushed by the weight of the air.
8. How do liquids and gases exert pressure?
Liquids and gases, collectively known as fluids, exert pressure on the walls and base of their container. This pressure is caused by the constant, random motion of their particles colliding with the container's surfaces. For liquids, pressure increases with depth because the weight of the liquid column above increases. Fluids exert pressure in all directions, not just downwards.
9. How are gravitational force and frictional force fundamentally different?
While both are common forces, they are fundamentally different in nature and how they act.
- Nature: Gravitational force is a non-contact force that attracts any two objects with mass, whereas frictional force is a contact force that opposes motion between two surfaces in contact.
- Condition: Gravity acts on all objects at all times, whereas friction only acts when there is an attempt at relative motion between surfaces.
- Direction: Gravity always acts towards the centre of the larger body (e.g., Earth), while friction always acts in the direction opposite to the motion or intended motion.
10. What would happen if there was no friction in our daily lives?
If there were no friction, life as we know it would be impossible. Friction is a necessary force that we often take for granted. Without it:
- We would not be able to walk; our feet would slip on any surface.
- Cars could not move, as the wheels would just spin in place, and the brakes would not work.
- We couldn't hold or pick up any object.
- It would be impossible to write with a pen or pencil.
- Nails and screws would not hold things together.
