# Force and Pressure

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.

### 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

1. 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.

2. Muscular Force - When force is caused or carried out by the action of muscles is called muscular force.

3. Magnetic Force - Force acting between two magnetic bodies as a result of their poles is called magnetic force.

4. 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.

5. 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 is called electrostatic force. In other words, the electrostatic force is an attractive or repulsive force acting between two electrically charged objects.

6. 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.

7. 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.

8. 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.

9. 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.

10. 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) = $\frac{ Force \; (Fn) }{Area \; (A) }$

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.

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.