Definition
To push or to pull an object is called as force. Basically, Force is an agent which can cause
the change in position, shape or size of the body. Or we can say that
- Force is an external effect in the form of a push or pull
which Produces or tries to produce motion in a body at
rest. - Stops or tries to stop a moving body.
- Changes or tries to change the direction of motion of
the body.
Out of so many natural forces, for distance 10โ15metre, nuclear force is strongest while gravitational force weakest. ๐นnuclear > ๐นelectromagnetic > ๐นgravitational.
The force is completely defined by its
- Magnitude
- The direction in which it acts and
- Point of application.
Unit
The SI unit of force is newton (N).
The force is a vector quantity, So If more than one forces act on an object, we can find the resultant
force by vector addition
EX โ 1 Three forces ๐ญ๐ = ๐๐ฬ+ ๐๐ฬโ ๐ฬ,๐ญ๐ = ๐๐ฬโ ๐ฬโ ๐๐ฬ ๐๐๐
๐ญ๐ = ๐๐๐ฬ+ ๐๐ฬ N act on a block of mass 5 kg. Calculate the net force on the particle.
๐นnet = ๐น1ย + ๐น2ย + ๐น3
๐นnet = (3๐ฬ+ 2๐ฬโ ๐ฬ) + (4๐ฬโ ๐ฬโ 2๐ฬ) + (23๐ฬ+ 3๐ฬ)
๐นnet = 7๐ฬ+ 24๐ฬ
Types of Force
Generally, forces are of two types โ
- Contact Force – Force which acts on a body when the body is in contact with the force is known as
contact force. Eg โ Normal force, String Force (Tension), Friction, Spring force etc. - Non-Contact Force – The force which acts on a body when the body is not in contact then the force is
known as non-contact force. Eg โ Weight, Electrostatic force, Magnetic Force
EX โ 2 A bullet of mass 40 gram moving with a speed of 90 m/s enters a heavy wooden block and is stopped after a distance of 60 cm. What is the average resistive force exerted by the block on the bullet?
After entering in the block, bullet will experience retardation and will stop at the end. So this
retardation will be given as
a = โu2/2s = 902/2 x 0.6 = โ6750 m/s2
So therefore the retarding force will be F = ma
F = 40/1000 x 6750 = 270 N
EX โ 3 Three forces ๐ญ๐ = ๐๐ฬ+ ๐๐ฬโ ๐ฬ,๐ญ๐ = ๐๐ฬโ ๐ฬโ ๐๐ฬ ๐๐๐
๐ญ๐ = ๐๐๐ฬ+ ๐๐ฬ N act on a block of mass 5 kg. Calculate the acceleration of the particle.
๐นnet = ๐ญ๐ + ๐ญ๐ + ๐ญ๐
๐นnet = (3๐ฬ+ 2๐ฬโ ๐ฬ) + (4๐ฬโ ๐ฬโ 2๐ฬ) + (23๐ฬ+ 3๐ฬ)
๐นnet = 7๐ฬ+ 24๐ฬ
| ๐น | = ๐น = โ(7)2 + (24)2 = 25 ๐
Acceleration of the block
๐ = ๐น/๐ = 25/5 = 5 ๐/๐ 2